What causes an air compressor to lock up?


Auto air conditioning compressor


What causes an air compressor to lock up?


  • Lack of lubrication
  • Cooling system poor performance
  • Condenser fan not working or performing poorly
  • A/C† system overcharged
  • Incorrect type of oil
  • Low refrigerant charge
  • A/C system contamination
  • A/C refrigerant cross contamination (Charging R-134a refrigerant into R-1234YF refrigerant.)
  • Inefficient condenser
  • Dirty evaporator core (In the past, not much attention was paid to dirty evaporators. Technicians are now beginning to realize that low evaporator pressures cause high compression ratios.)

Analysis of Denso A/C Compressor warranty claims shows that in a quarter of all cases
the use of incorrect oils, such as universal oils or oil mixtures, inevitably leads to seizure and damage. This is because universal oils are PAO-oils or mineral oils with a different viscosity to that of synthetic PAG-oils. PAO-oils do not mix well with PAG-oils and with refrigerant R134a or R1234yf, leading to poor lubrication and increased wear. Installing the ac Compressor without balancing the oil in the system, gives a high risk of liquid lock, due to too much oil in the A/C system! When adding oil to the ac compressor in your car one out of two methods could be used and the right one will depend on the type of compressor. Oil could be added through the ac compressor oil service port or through the low side or intake of the compressor. Always add oil through the oil service port if it comes with one or compressor damage may result.
Excessively high temperature and†lack of lubrication†are the biggest enemies of any automotive a/c compressor bearings. Slipping compressor clutches can generate†temperatures as high as 1,200 degrees Fahrenheit; this tremendous amount of heat will quickly melt down the bearing seal. The bearing loses its grease and in the process, before it locks up completely it gets rough and noisy. †Seal could cause the compressor oil to finds it way into the hvac compressor clutch bearing contaminating the grease. The properties of the bearing grease will be changed by this oil contamination causing it a poor compressor bearing lubrication and inevitably internal bearing failure.
Leaking air conditioning systems†will leak out refrigerant and the oil that resides inside of the compressor creating a huge frictional resistance between the compressor piston and the cylinder leading to an increase in compressor internal temperature
Overcharged or improperly vacuumed auto ac systems will create high system pressures and therefore high temperatures.
Compressor pressure plate and rotor pulley excessive air gap will cause slippage and rise in temperature.
A dirty evaporator will cause the suction pressure to drop. When the suction pressure goes below normal, the vapor that the compressor is pumping becomes les dense and gets thin (sometimes called rarified vapor).The compressor performance declines. Low suction pressures also cause the high-pressure gases caught in the clearance volume of the compressor to expand more during the pistonís downstroke.This gives the compressor a lower volumetric efficiency. These gases have to expand to a pressure just below the suction pressure before the suction valve will open. Because more of the downward stroke is used for expansion, less of the stroke can be used for suction. Suction ends when the piston reaches bottom dead center.

How to save my auto air conditioning compressor?


A/C performance test

This easy test will give you a general guideline to compare against your carís a/c operation. (This test was specifically performed on a BMW model).
Switch on air conditioning compressor with A/C button at a vehicle interior of 45 įC /113 įF (measure at the head restraint)

On vehicles with MAX-AC button:

  • Activation of †MAX- AC (= maximum cooling power)

On vehicles without MAX-AC button:

  • Set Maximum cooling power by means of following steps:
    • Setting low temperature value
    • Blower setting maximum
    • Stratification maximum cold(4 blue bars)
    • Only ventilation open
    • Close remaining flaps (air outlet only from center fresh air grille, left and right)

After 5 min, measure both ventilation temperatures with a thermometer at the same time (center, left and right fresh air grille).†The measured temperature must be < 16 įC / 60.8 įF and the difference between right and left may not be greater than 2 įC / įF.

How to find an automotive compressor problem, before is too late?

Compression ratios are used to compare pumping conditions for a compressor. When compression ratios become too high, the refrigerant gas temperature leaving the compressor rises to the point that oil for lubrication may become overheated. Overheated oil may turn to carbon and create acid in the system shortening the life of the Automotive A/C system.


Ambient temperature

High Side Pressure

Low Side Pressure

90 įF/32įC 250-270 psi /1724-1862 kPa 45-55 psi / 310-379 kPa



Calculation example:

Compression ratio =†Absolute Discharge

†††††††††††††††† ††††††††††††Absolute Suction


CR=†250 psig + 14.7 atmosphere

††††††† 45 psig + 14.7 atmospheres


CR =†264.7



CR = 4.43:1

Understanding the A/C compressor compression ratio results.
A compression ratio of 4.43:1 would indicate to a service technician that the absolute or true discharge pressure is 4.43 times as great as the absolute suction pressure. Either an increase in head pressure or a decrease in suction pressure will cause higher compression ratios.

Symptoms of a Bad or Failing AC Compressor


  1. Growling noise with compressor disengaged
  2. Whistling noise
  3. Grinding noise
  4. Squealing noise
  5. Rattling noise
  6. Growling noise with compressor engaged
  7. Banging noise
  8. Knocking noise

Serpentine belt problems usually result from one of these causes: a defective belt tensioner, misalignment of a pulley or defective bearings of any component of the drive system.†Worn out drive system belts lead to poor†hvac compressor output performance.

Can compressor be repaired?

The air compressor may be remanufactured or rebuilt. The price range for labor only is $285.00 to $500.00.This is an option many people choose, because of the price difference between a new compressor and a rebuilt one.

What happens if a compressor fails?

The first sign will be no cold air coming out from the vents.
These are all signs that a/c compressor in your car is about stop working or fail:
1-Clicking sound from under the engine. (Compressor clutch engaging and disengaging)
2-AC not working.
3-Noise under the engine with the a/c climate control on.
4-Burned rubber smell coming out from the engine compartment.
5-Looking at ac gauges set pressure; typical weak or damaged ac compressor pressures are High side pressure too low and Low side pressure too high.
When a compressor begins to have an internal failure. It often releases debris into the A/C system. The debris created can be metal or Teflon. Metal debris can be created from any metal component inside the compressor sefl-desctructing, and Teflon can come from the Teflon seals on the compressor pistons. When debris becomes trapped against the seal, it will damage it and pieces of the seal break apart and travel throughout the A/C system.
When enough debris is present, it can become trapped in the various components, and restrict the flow of refrigerant and oil.
After a catastrophic compressor failure the system must be flushed, otherwise the new air conditioning compressor could get damaged by all the debris released by the old locked up a/c compressor.
Most vehicle manufacturers recommend closed loop flushing with refrigerant as a flushing agent. A benefit of this type of flushing is there is no danger of flush contamination, since the flush agent being used is the correct refrigerant for the A/C system.
When the A/C system flushing is complete:

  • Oil balance the system through the compressor.
  • Reconnect the manifold line to the compressor, or replace the compressor if needed.
  • Install a new orifice tube or TXV.
  • Install a new Accumulator-drier or Receiver-drier


Why did my compressor stop working?

  • Electric or electronic fault of any of the compressor control devices or ac compressor circuit protection device
  • Faulty or wrong signal input to the BCM or PCM.
  • A/C compressor clutch excessive air gap.
  • A/C system too low on refrigerant charge due leakage in the air conditioning system.
  • Compressor clutch coil winding open.
  • A/C head control set switch damage or entire a/c control set damaged.
  • Variable displacement electronically controlled compressor. Valve control damaged.


Why does the compressor cycle on and off?

What causes a compressor to short cycle?

Low refrigerant charge causes rapid cycling.

Drive belts and blower resistors do not affect compressor cycling.An excessive air gap may prevent the clutch from engaging.

Auto ac repair in miami Free estimates and check ups by ase certified tech


Defrost Mode.Damage to compressor due to low refrigerant charge.

On many vehicles, by selecting the defrost position on the controls, it will also activate the A/C compressor. Cooling the air with A/C first will remove more moisture from the air so it can do a better job clearing the windows.If the A/C system is not functioning correctly this ability will be lost. If your A/C system is not working 100%,with low refrigerant charge over the winter months, youíre not getting the refrigerant oil back to the compressor which is damaging it all winter season that will lead to costly repairs in the spring time. If you run into any issues regarding this system have a professional mechanic from Auto A/C Repair. help you diagnose and fix it.
Call Auto A/C Repair LLC. !
Ph:(786) 483-9406

ac temperature out of the vents

How often does an AC system need to get recharged?


The A/C system in your car is a closed sealed system. It may never need to be recharged. The refrigerant inside the system is pressurized by the hvac compressor ,recirculated and reused in a closed loop infinite system. The Freon(refrigerant) will change from vapor to liquid and back constantly for as long as the system is running.

The R-134a/R-1234yf install in your car is in charge of moving the unwanted elevated temperature of one room or space (the cabin inside your car ) to the outside ambient temperature where it has no impact. To accomplish this task properly a factory calculated range amount of refrigerant needs to be running inside the system.

You need to get your AC system recharged as soon as the total amount of refrigerant is too low to carry the heat from inside your car’s cabin to the outside of the vehicle.

100 % sealed air conditioning system does not exist. All a/c systems leak, and this condition is taken into consideration when the a/c charge amount is calculated when designing the system. Some amount of refrigerant loss could develop over time, but it is a minute amount, and it should not affect system operation.

How do I know if my ac in my car needs to be recharged ?

There is not a periodic service interval that you need to follow to recharge your air conditioning system. This service is system dependent, meaning every car will have unique needs for freon(refrigerant) recharge.

The first sign that could indicate that you need to recharge the refrigerant in your car’s ac system is when the system begins to cool less than it used to.


  • Poor A/C performance. A/C not cooling down the vehicle
  • One Side of the car cooling more than the other side.
  • Back of the car cooling more than the front.
  • A/C compressor short cycling. A/C compressor turning on and off fast.
  • Frost in a/c lines.
  • Visible refrigerant (Freon) leaks.


Low refrigerant could mean low oil circulating and improper lubrication of the hvac compressor. Therefore when there has been a refrigerant leakage big enough the compressor gets to the point where there is not refrigerant to pump and then it pumps out the oil that lubricates the compressor’s internal components. Failure of the a/c compressor will result if the ac system is not recharged, and oil balanced properly.




The refrigerant in the automotive system is the substance which not only transfer heat from the passenger compartment in the vehicle to the condenser outside of the car and then released the heat into the atmosphere, but it also cools the compressor down reducing the total heat of compression preventing the compressor from building up excessive pressure and temperature. A poor lubricated compressor could be operating in temperatures that could get up to 800 F



Electronic controlled variable displacement compressors could be clutch or clutch-less designs. The ac  compressor has a swash plate that rotates to reciprocate pistons, which compress refrigerant. The swash plate is allowed to change its angle which changes the stroke rate of the piston. They are electronically controlled using sensors and an Electronic Control Module (ECM)

Electronic controlled variable displacement compressor is always running even when the a/c is off. The ECM changes the rate of displacement, but the compressor is spinning connected to the drive belt without any clutch to disengage.

Lubrication occurs by using a sump in which the connecting rod splashes oil around the inside of the compressor. Some automotive air conditioning compressors use an oil pump to circulate the oil, like an engine lubrication system. Lubrication is accomplished while the ac compressor is running and there is refrigerant and oil circulating back to the compressor.

The (ECVD) clutch-less compressor should not be operated  without refrigerant in the system  to carry lubricant.


 These (ECVD) clutch-less compressors do not have a conventional clutch, meaning the compressor shaft turns all the time driven by the accessory drive belt, even when the a/c is commanded  off from the hvac temperature control assembly panel!



Source: ALLDATA Repair.


Variable Swash Plate Compressor

The internally controlled variable swash plate compressor changes the swash plate angle by a MCV (Mechanical Control Valve) in accordance with fluctuation of a suction pressure.

The externally controlled variable swash plate compressor changes the swash plate angle by an ECV (Electric Control Valve) in accordance with an electrical signal from the heater & A/C control unit.


Without the right tools This new compressor output control technology can make it difficult to determine if the poor ac performance is being caused by a computer control malfunction or another problem in the refrigeration system or cooling system of the vehicle. This can result in an expensive misdiagnosis and unnecessary compressor replacement.

These are different tools that could be used for correct testing a diagnose of this units:

1.   A scan tool and checking PWM signal from the module to the ECV compressor .

2.  Handheld ECV Compressor tester unit to manually control the ECV on the compressor and increase or decrease (PWM)  the pumping capacity of the air conditioning.

3.  A scope can be used by carefully back probing the connector to the control valve and connecting the scope leads to the two wires and check the PWM wave signal


With a large refrigerant undercharge, oil is pumped out from the compressor and becomes trapped in the evaporator or other ac components of the system and is unable to properly return to the hvac compressor. The amount of oil in the compressor can get down to dangerously low levels creating excessive heat and, in most cases, leading to failure of the unit. Some Air conditioning tests has shown that with an undercharged ac system, the oil amount in the compressor was reduced by over 57%.

  1. Poor ac performance  
  2. Growling noise
  3. Whistling noise
  4. Grinding noise
  5. Squealing noise
  6. Rattling noise
  7. Banging noise
  8. Knocking noise


Car A/C air conditioning compressor clutch bearing.

Automotive a/c compressor clutch bearing failures are usually caused by system problems and not the bearing itself. Replacing the noisy bearing without finding the root of the problem and fixing it permanently will only lead to premature damage of a new component and a waste of time and money. Seals, compressor shaft and bearing could share the same enemy, heat.

What could cause damage to the ac compressor bearing in my car ?

  1. Excessively high temperature and lack of lubrication
  2. Slipping compressor clutches
  3. Over tensioned manual belt tensioners
  4. A leaking compressor shaft seal

A leaking compressor shaft seal could cause the compressor oil to find its way into the hvac compressor clutch bearing contaminating the grease. The properties of the bearing grease will be changed by this oil contamination causing it a poor compressor bearing lubrication and inevitably internal bearing failure.


What could cause the ac system in my car to buildup excessive high pressure and temperature ?

  1. Leaking air conditioning systems will leak out refrigerant and the oil that resides inside of the compressor creating a huge frictional resistance between the compressor piston and the cylinder leading to an increase in compressor internal temperature.
  2. Overcharged or improperly vacuumed auto ac systems will create high system pressures and therefore elevated temperatures.
  3. Compressor pressure plate and rotor pulley excessive air gap will cause slippage and rise in temperature.

Replacing just the bearing

A/C compressor factory bearing defects will not  need more than a few hours of compressor operation to become evident. Rarely the bearing itself is the culprit.


Different types of oil

how much oil does my car ac system need ?

how much oil does my car ac system need ?

Proper lubrication is a must for ac compressor long life. When the a/c compressor is operated ,oil gradually leaves the compressor, and the oil is circulated through the entire ac system together  with the refrigerant. After the air conditioning system is operated for the first time an oil balanced condition is reached in which a certain amount of oil is retained in the compressor and a certain amount is re-circulated through the ac system components with different amounts of oil depositing in them . If a component of the system is replaced after the system has been operated, we need to compensate for this by adding oil to the new replacement ac part.


Too much oil in the a/c system could result in extremely high head pressures which will cause poor air conditioning performance and premature wear and failure of the hvac compressor. If there is a surplus of oil in the system, too much oil circulates with the refrigerant ,causing the cooling capacity of the system to be reduced and the compressor head pressure to increase. Too little oil results in poor lubrication of the compressor and an increase in the heat of compression which shorten the life of the ac compressor.


When there has been excessive leakage of refrigerant, or it is necessary to  replace a component of the refrigeration system oil balancing is necessary to assure that the total oil charge in the system is the correct one after the leak has been repaired or the new ac part is installed in the car.


The recommended procedure step by step

  1. Measure the oil recovered from the system while recovering the refrigerant prior to part replacement
  2. Drain and measure the oil left in the old part
  3. Drain the new part(if factory oil-prefilled)
  4. Refill the new part with the same amount of oil removed from the old part and the amount of oil recovered from the system


The refrigerant oil required by the automotive ac system depends on a number of factors ,but it is primarily dictated by the type of refrigerant used in the system.R-12 car systems used a mineral oil. Mineral oil mixes well with R-12  without breaking down and losing its lubrication characteristics. Mineral oil however cannot be used  to lubricate ac systems with R-134a refrigerant.R-134 systems require a different synthetic oil,polyalkylene glycol (PAG).There are different blends of PAG and POE oil; always use the recommended by the vehicle manufacturer or the replacement part manufacturer.

The lubricant oil used in automotive air-conditioning systems is a non-foaming, sulfur free grade specially formulated for use in cars a/c systems. New refrigerants like R-1234yf might use PAG 46 and are backwards compatible for use with R-134a systems, but the R-134a old PAG 46 oils are not forward compatible with R-1234yf systems.


Add the recommend refrigerant  oil in the amount listed if you replace any of the following parts:
A/C condenser(including receive Dryer. 25 mL (5/6 fl oz)
Evaporator 40 mL (1 1/3 fl oz)
Line or hose 10 mL (1/3 fl oz)
Receiver/dryer 10 mL (1/3 fl oz)
Leakage repair 25 mL (5/6 fl oz)
A/C compressor For A/C compressor replacement, subtract the volume of oil drained from the removed A/C compressor from 82 mL (2 3/4 fl oz), and drain the calculated volume of oil from the new A/C compressor: 82 mL (2 3/4 fl oz) Ôľć Volume of removed A/C compressor = Volume to drain from new A/C compressor.
NOTE: Even if no oil is drained from the removed A/C compressor, do not drain more than 50 mL (1 2/3 fl oz) from the new A/C compressor.


How to add oil to air conditioning compressor ?

Different types of oil


How important is oil in A/C compressors ?



Oil in the A/C system is essential, primarily to lubricate moving parts, i.e., the compressor. It also enables heat to travel and dissipate from the compressor. As with refrigerant, oil in the A/C system must keep its chemical stability.


Insufficient lubrication due to the wrong type of oil and viscosity is the second most frequent reason for A/C compressor damage and failure.


Distinct types of a/c oil like PAG,POE or mineral oils with a different viscosity do not mix, leading to poor lubrication, damaged seals and increased automotive air conditioning compressor wear


The use of the wrong type of oil could result in the hvac compressor‚Äôs piston rubbing against the cylinder surface. If the oil is too thick, it is unable to properly lubricate the tight space between the cylinder wall and the piston. Wrong oil viscosity can result in more internal friction, leading to an increase in compressor temperature and inevitably compressor damage.


Blending or mixing of diverse types of oils may result in a new different type and oil viscosity. This oil contamination build-up to the point where it can block the flow of refrigerant and oil, leading to poor lubrication and seizure of the compressor and major system failure.



Refrigerant moving oil and cooling down the A/C Compressor


it is extremely important that the engine not be run on a vehicle with a clutch less compressor if there is no refrigerant in the A/C system. This is because the compressor depends on refrigerant to carry lubricant inside of it.



How much oil should I add after a/c compressor replacement ?


After the refrigerant system has been charged and ran at the factory, the refrigerant oil in the A/C compressor is dispersed throughout the refrigerant system. The A/C receiver/drier, A/C evaporator, A/C condenser and the A/C compressor will each keep a significant amount of the needed refrigerant oil.

The refrigerant oil level in a new A/C compressor must first be adjusted prior to compressor installation.


Oil balancing the a/c system:

  1. Measure the oil recovered from the system by recovery/recycling/recharging station.
  2. Drain and measure the oil left in the old compressor using a beaker.
  3. Drain the new compressor and refill it with the same amount of oil removed from the system and old compressor .
  4. For Example :if 2 oz of oil are recovered from the system and 2 oz of oil was drained from the old a/c compressor, drain the new replacement a/c compressor and then add 4oz of the proper oil type and viscosity to the compressor before installation.



Installing the ac Compressor without balancing the oil in the system, gives a considerable risk of liquid lock, due to too much oil in the A/C system! When adding oil to the ac compressor in your car one out of two methods could be used and the right one will depend on the type of compressor. Oil could be added through the ac compressor oil service port or through the low side or intake of the compressor. Always add oil through the oil service port if it comes with one or compressor damage may result.


Most reclaim/recycling recharging stations will measure the lubricant being removed during recovery. This amount of lubricant should be added back into the system after the repairs are done.


How could the oil in my car’s A/C system be low?



Leaking automotive air conditioning systems will leak out refrigerant and the oil that resides inside of the compressor.

Refrigerant oil must be added when an A/C condenser, A/C receiver/drier or A/C evaporator is replaced

Refrigerant oil loss will be evident at the leak point by the presence of a wet, shiny surface around the leak.


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Why Isn’t My Car Heater Working?

Why Isn’t My Car Heater Working?¬†


In many cases, problems with the heating system are problems with the engine’s cooling system. Therefore, most service work and diagnosis are done to the cooling system. In some cases, the heater core is the problem. In some vehicles, it is possible to make repairs to vacuum hoses and electrical connections without removing the heater assembly. If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core. 

Heater Core

Why is my car heater not getting hot enough?

  • Air pockets in the heater core can interfere with proper coolant¬†circulation. Air¬†pockets form when the coolant level is low or when the cooling system is not properly filled after draining it.¬†
  • A gurgling noise in the heater core may be caused by a low coolant level in the cooling¬†system. A¬†low coolant level will allow too much air in the cooling¬†system. The¬†excessive air will mix with the coolant and create the gurgling noise.¬†
  • A restricted heater core will also cause a gurgling noise from the coolant passing through the restricted area.¬†
  • Coolant leaks. Internal engine coolant leakage is probable the¬†worst-case scenario.¬†
  • The engine thermostat is staying open and the vehicle¬†doesn‚Äôt¬†reach operating temperature.¬†
  • Heater control valve malfunction.¬†
  • Blend door actuator motor malfunction.¬†


How do I fix the heater in my car? 

Problems that pertain specifically to the heater are few: the heater control valve and the heater core. Most often, if these two components are faulty, the engine’s cooling system will be negatively affected. Both items are replaced, rather than repaired

How to diagnose the cause of temperature control problems? 

When diagnosing a heating system that is inadequate, it is imperative that you follow a logical diagnostic routine: 

  • Make sure there is adequate coolant in the cooling system.¬†
  • Verify that the engine reaches normal operating temperature.¬†
  • Verify engine thermostat operation.¬†
  • Check if there is flow through the heater core.¬†
  • Check proper operation of the heater control valve.¬†
  • Check with a Scanner Blend Door Actuator Motor operation.¬†


How can I tell if my heater core is clogged? 

If the engine is reaching operating temperature and the heater output is not acceptable, the next step is to check to see that there is flow through the heater core. Some systems use a heater control valve .These valves may be controlled by vacuum, electricity, or a cable. Be sure that the valve changes position, allowing coolant into the heater core. If that area is good or not applicable, check the inlet and outlet temperatures or the heater hoses at the core. If one is cold, you have a restricted core. If both are hot and equal, you may have restricted fins on the outside of the core, or the blend door may not be opening to allow the blower to move air across the core. There will be some drop in outlet temperature if everything is working normally. Usually this would be 10-30 degrees. A drop more than that means the core is restricted.

How to diagnose window fogging problems in my car? 

A leaking heater core is often the cause of a windshield fogging problem. Windshield fogging is the result of hot and humid air that condenses on the cooler glass. 

A sticky film on the inside of the windshield may be caused by: 

  • A coolant leak in the heater core.¬†
  • Under this condition the coolant level in the radiator should be¬†checked.¬†
  • A plugged air conditioning/heater case drain that allows water to¬†collect in¬†the case can become stagnant and produce a very¬†pungent¬†odor in the passenger compartment.¬†
Can you unclog a heater core? 

Heater cores are replaced, rather than repaired. Like the radiator, heater core tanks, tubes and fins can become clogged over time by rust, scale, and mineral deposits circulated by the coolant. Heater core failures are caused by leakage or clogging. Feel the heater inlet and outlet hoses while the engine is idling and warm with the heater temperature control on hot. If the hose downstream of the heater valve does not feel hot, the valve is not opening. 

If the heater core appears to be plugged, the inlet hose will feel hot up to the core, but the outlet hose will be cool.

How to try to unclog the heater core? 

flushing the heater core

Reverse flushing the core with a power flusher may open the blockage, but usually the core must be removed for cleaning or replacement. 

  • Check¬†the inlet and outlet temperatures or the heater hoses at the core. If one is cold, you have a restricted core. If both are hot and¬†equal,¬†you may have restricted fins on the outside of the¬†core,¬†or the blend door may not be opening to allow the¬†blower¬†to move air across the core.¬†
  • There will be some drop in outlet temperature if everything is working normally. Usually this would be 10-30¬†degrees. A drop more than that means the core is restricted¬†


Cleaning a clogged evaporator/heater case drain tube often eliminates a windshield fogging problem. If the drain is clogged, a leaking heater core will allow engine coolant to accumulate in the housing. A clogged drain also allows condensed water vapor to accumulate. Both problems add moisture to the air, which tends to fog the windshield. 

What is the average cost to replace a heater core?

The average cost for heater core replacement is between $580.00 and $980.00. Labor cost will depend on the make, model, and year of the vehicle. In most cases the entire removal of the dashboard is necessary to gain access to the heater core. 

How many hours does it take to replace a heater core? 

2015 BMW 320i Sedan (F30) L4-2.0L Turbo (N20) 

The Heater core replacement labor time in this vehicle is 9.1 hrs. 



-2013 Toyota Corolla L4-1.8L  

The Heater Core replacement labor time in this vehicle is 5.2 hrs. 


-2010 Ford Truck F 150 2WD V8-4.6L

The Heater Core replacement labor time in this vehicle is 5.9 hrs.


-2010 Volkswagen Jetta Sedan (1K2) L4-2.0L DSL Turbo

The Heater Core Replacement labor time in this vehicle is 2.8 hrs. 


On-site automotive ac service

Why my car A/C is stuck in heat mode when the cooling mode is on?


A malfunctioning Temperature Blend Door Actuator Motor could be the cause. When the Winter Season begins, and you try to change the A/C settings on the Air Conditioning Climate Control from Cold air to hot air and you cannot control the air temperature.


What is a blend door actuator?



2 Temperature Blend Door Actuator Motor



The blend door actuator is a small electric motor. As you adjust the temperature up and down, the signals go through the actuator to complete the request, positioning the air door on the right position.

When A/C became a popular option on vehicles in the mid to late 1970s, the systems were simple, except for some high levels vehicles, which were often the test bed of things to come.

The control systems were cable actuated, and eventually, vacuum controls were introduced. Most systems were equipped with a heater control water valve, also cable or vacuum controlled.

Automatic temperature control systems had a range of controls: vacuum, electromechanical, and pure electronic devices. They were complicated for the time and often not reliable.


The air delivery system controls the movement of heated and cooled air into and throughout the passenger compartment. The Hvac housing is the plenum unit located and beneath the instrument panel. It contains the evaporator and heater core, and the blower motor assembly and the blower speed control device.

The plenum houses the air doors and door actuators that direct airflow to the correct ductwork. The doors ay be controlled by cables, vacuum, or electrical actuators. Single zone systems are usually equipped with three doors:


The Blend Door Actuator ‚Äď the blend door determines the temperature of the air flowing through the passenger compartment. If the A/C is operating, the air is dehumidified and cooled. The more air the blend door directs through the heater core, the warmer the air entering the passenger compartment.


Dual zone systems operate in the same manner as single zone systems. However, most dual zone systems use two blend doors: one for the driver side and the other for the passenger side. This design allows for separate temperature settings on each side for the vehicle.



Actuator motors used in automotive Hvac systems can be one of four designs, depending on vehicle manufacturer, system design, year, and model of the vehicle:

  • Tri-state
  • Bi-directional
  • Three wire
  • Two wire

Tri-state Actuator

Temperature Blend Door Actuator Motor

2 Temperature Blend Door Actuator Motor


A tri-state actuator is a five-wire design. Three of the five wires are used for the feedback circuit. The other wires are for ignition voltage and Hvac control head requests.

0 volts will move the motor one way, 5 volts will drive the motor in the other direction, and when the signal wire reads 2.5 volts, the motor stops rotating.

Bi-directional Actuator Motor

Bi-directional actuators use three wires for circuit feedback. The other two wires are the positive and negative circuits that drive the motor. These circuits are controlled by the Hvac control head and move the motor direction based on the selections made at the control head.

Temperature Blend Door Actuator Motor

2 Temperature Blend Door Actuator Motor
Three Wire Actuator Motors

Three wire actuators have a power, ground, and an input wire from the Hvac control head. These actuators use a preprogrammed logic chip containing all the information to drive the motor in the requested direction. When a position change is requested by the vehicle operator, a circuit in the control head sends voltage to the actuator motor. As the motor moves, a potentiometer in the actuator compares the motor voltage to the output voltage from the control head. When both voltage readings are the same, the actuator motor stops. There is no feedback to the control head with this design.

Two Wire Actuator

Two wire blend door actuator motor

3 Temperature Blend Door Actuator Motor


Two Wire actuators create electrical pulses when the commutator rotates across the brushes of the motor. The Hvac control head, which has pre-programmed logic and actuator endpoint references, counts the electrical pulses as the motor moves the door through its sweep from one end to the other end. The actuator endpoints will change as the door seal wears, so if the endpoint counts become too large, a DTC will be set. If the Hvac system loses power, or if a component is replaced, the endpoints must usually be relearned through a calibration process.


How do I know if my blend door actuator is bad?

Binding Actuators

If an actuator binds inside the Hvac plenum, the control module will attempt to overcome the restriction several times before it shuts down the circuit. You will hear the ticking noise. If the binding clears on the next activation, the control module will perform a calibration and set a history DTC.


What does a bad actuator sound like?

If an actuator binds inside the Hvac plenum, the control module will attempt to overcome the restriction several times before it shuts down the circuit. You will hear the ticking noise from the actuator motor.

Where is the heater blend door actuator located?

automotive dashboard

The Blend Actuator Motor is located on the Hvac Box underneath the dashboard. The exact location of the Actuator will depend on the Make, Model and Year of the vehicle serviced.

1 Left temperature actuator screws
2 Temperature blend actuator
3 Left temperature actuator lever
5 Hvac Box

Actuator motor

2015 Cadillac CTS Coupe RWD V8-6.2L SC

How do you test a blend door actuator?

Actuator diagnosis

When diagnosing Hvac actuators, always check the door for binding or restriction, caused by a distorted, worn, or damaged plenum. Check for restrictions that may be caused by a foreign object that is lodged in the door seep, or a broken crank arm on the door assembly.

Do not operate an actuator that is not attached to the door on the plenum. If the door is not attached, the motor can drive past its limits, which usually results in damage to the actuator.

What tools to use for door actuator diagnostics?

Actuator motor operation can be checked with a digital multimeter. Using service information and wiring diagrams for the vehicle, find the correct connector pins for feedback, power, and ground circuits on the actuator. Carefully back probe at the pins, taking care not to pierce the wiring insulation or cause damage to the connector pins. With the meter set on the DC volts scale, move the Hvac selector know and watch for a voltage change as the door position is commanded to change. There should be a voltage change as each position is selected.

  • Digital Multimeter
  • Service Information and Wiring diagrams
  • Scanner

These voltage readings will not give the exact position of the door. However, they will indicate that the door is moving through a complete sweep from one endpoint to the other.

How long does it take to fix a blend door actuator?

The labor time will be different depending on the make, model, and year of the vehicle and if it is a dual zone system or single. The labor will increase because of the time needed to remove all components before we can gain access to the actuator. In some model’s complete removal of the entire dashboard is needed to gain access to the Blend door actuator motor.


2015 Dodge or Ram Truck RAM 1500 Truck 2WD V6-3.0L DSL Turbo

Temperature blend door motor

Left side: 0.5 hours

Right side: 5.2 hours


2013 Ford Focus 2.0L

Temperature blend door motor replacement

Driver side: 0.5 hours

Passenger side: 0.5 hours

How can i make my car ac colder

Problem Symptoms Table

Before replacing or repairing air conditioning components, first determine if the malfunction is due to the refrigerant charge, air flow or compressor.

Use the table below to help you find the cause of the problem. The numbers indicate the priority of the likely cause of the problem. Check each part in order.

How to Diagnose Your Car’s Air Conditioning System?

Symptom Suspect area
No blower operation 1.       Blower fuse
2.       Blower relay
3.       Blower motor
4.       Blower motor resistor
5.       Blower speed control switch
6.       Wire harness

No air temperature control

1.       Engine coolant capacity
2.       Heater control assembly
3.       Temp actuator
No compressor operation 1.       Refrigerant capacity
2.       A/C fuse
3.       Compressor
4.       A/C pressure transducer
5.       A/C pressure switch
6.       Evaporator temperature sensor
7.       Wire harness
No cool comes out 1.       Refrigerant capacity
2.       Refrigerant pressure
3.       Drive belt
4.       Compressor
5.       A/C pressure transducer
6.       Evaporator temperature sensor
7.       A/C switch
8.       Heater control assembly
9.       Wire harness
Insufficient cooling 10.   Temperature actuator
1.       Refrigerant capacity
2.       Drive belt
3.       Compressor
4.       Condenser
5.       Expansion valve
6.       Evaporator
7.       Refrigerant lines
  8.       A/C pressure transducer
9.       Heater control assembly
No engine idle-up when A/C switch ON 1.       Engine ECM
2.       Wire harness
No air inlet control 1.       Heater control assembly
2.       Intake actuator
No mode control 1.       Heater control assembly
2.       Mode actuator
3.       Intake actuator
No cooling fan operation 1.       Cooling fan fuse
2.       Fan motor
3.       Engine ECM
4.       Wire harness


ac temperature out of the vents

How do I check the temperature of my car AC?

How do I check the temperature of my car AC?



How do I check the temperature of my  2015 Mazda 6 AC?

1. Measure the air conditioner output temperature after approx.10 min have elapsed from engine start.

2. Place a dry-bulb thermometer in the driver-side center Vent outlet.

  1. Start the engine and warm it up.

    4. Set the fan speed to MAX HI.

    5. Turn the A/C switch on.

    6. Set to RECIRCULATE mode.

    7. Set the temperature control to MAX COLD.

    8. Set to VENT mode.

    9. Close all the doors and windows.

    10. Maintain the engine speed at 1,500 rpm.

    11. Wait until the air conditioner output temperature stabilizes.

    Stabilized condition
    –¬†The A/C¬†compressor¬†repeatedly turns on and off at regular intervals.

    12. After the blower air is stabilized, read the dry-bulb thermometer.

    13. Verify the ambient temperature.

    14. Verify that the temperature reading is in the shaded zone.



41 F

39.5 F

50 F

4.5 F

59 F

41 F

68 F

42 F

77 F

43 F

86 F

43.5 F

95 F

47 F


50 F


We could easily know what should the a/c temperature be at the vents be checking this manufacturer chart. If the A/C system in the car is working properly the temperature should be near these values.

ac temperature out of the vents

How cold should my AC be at the vent in my car?

The ambient air temperature must be at least 16¬įC (60¬įF) .

Do not induce additional air flow across the front of the vehicle during the test.


What temperature should the A/C blow ? 

The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. During periods of high heat and humidity, an A/C system will be more effective in the Recirculation mode (MAX-A/C).

We could easily know what should the A/C temperature be at the vents be checking this manufacturer chart. Taking into account  50-60 % relative humidity and an ambient air temperature of 77 F,86 F,95 F ,the discharge air temperature at the center vent should be in the range of :

50-54 F

56-60 F

63-70 F

if the A/C system in the car is working properly.

How cold should my AC be at the vent in my car?

A performance test is the best way to determine whether the system is performing up to design standards. This test also provides valuable clues as to the possible cause of trouble with the A/C system.

How do I check the temperature of my car AC?

Testing must be performed as follows:

Vehicle location Indoors or in the shade (in a well-ventilated place)
Doors Closed
Door Windows Open
Hood Open
Mode switch Front (ventilation) set
Recirculation switch Set (in-cabin recirculation ) set
Blower Max. speed test
Engine speed Idle speed
Operate the air conditioning system for 10 minutes before taking measurements




Recirculating-to-discharge Air Temperature Table

Inside air(Recirculation air) at blower assembly inlet  

Discharge air temperature at center vent


Relative humidity


Air temperature




77 F


86 F


95 F



77 F


86 F


95 F


***This values are for NISSAN-DATSUN Maxima V6 3.5L***