What causes an ac compressor to lock up

What causes an ac compressor to lock up

Inaccurate refrigerant(freon) charges increase the chances of auto ac compressor lock up. Modern auto a/c systems require super accurate charging. Being off as little as 2 ounces can cause problems.R-134a and R-1234yf ac system tolerances require charge rates that must remain or should be charged within +/- 5% of OEM recommendation. SAE J2788 requires charge accuracy of +/- one-half ounce.

Attempting to charge by cans is History !!

Car ac compressor lock up due to improper compressor lubrication.

Refrigerant moves the oil inside the ac system and helps to cool down the ac compressor. An undercharge or overcharge refrigerant condition will increase the air conditioning compressor temperature and a change in oil viscosity and lubrication characteristics. Most compressor lock ups are the result of a lubrication problem.

AC compressors lock up due to ac system contamination

Auto ac compressor damage may occur because of system contamination. Anything more than the correct type of freon and oil is a contaminant. The use of sealers to fix small refrigerant leaks will cause oil and refrigerant contamination and ultimately ac compressor lock up. Sealer can’t be removed from the A/C systems. The contaminated components must be replaced.

The use of excessive Dye to help finding leaks in the ac system could create a contamination problem as well, increasing the normal working pressure of the ac compressor and the overall efficiency of the air conditioning system.

Improperly replacing any component in the automotive air conditioning system where the system must be opened for replacement of the damaged part and not evacuating the system before recharging it with the proper amount and type of refrigerant will contaminate the ac system with air. Air and moisture inside the system will create excessively high operating pressures and temperatures and eventually could lead to a compressor lock up.

Inefficient ac condensers and air conditioning compressor lock up

Debris on the condenser will affect the desuperheat, condensation and subcooling processes happening in the auto ac condenser.AC condenser with bent or missing fins will be unable to efficiently operate. An inefficient ac condenser will cause an auto ac compressor to lock up.

Low Refrigerant charge and electronically controlled compressor lock up ?

The car engines in vehicles with the clutchless compressors should not be run without refrigerant in the A/C system. Without refrigerant to move the oil, the auto ac compressor may not be properly lubricated and compressor lock up may result.

Do you need assistance inspecting the state of your ac compressor in your vehicle?

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ac compressor oil

Why does the compressor cycle on and off?

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.

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Why is my car a/c not cooling ?

This is a list of the most common car a/c failures that lead to a no cooling ac condition in any vehicle:

  • A/C Refrigerant leaks
  • A/C Refrigerant contamination
  • A/C Refrigerant overcharge condition
  • A/C system non-condensable gases contamination
  • A/C refrigerant oil ,overcharge condition
  • Weak A/C Compressor
  • Faulty valve, on electronically controlled variable displacement a/c compressor  
  • Faulty A/C Compressor Clutch Relay
  • Faulty A/C Compressor clutch coil
  • Inoperative A/C Compressor
  • Engine cooling system affecting A/C operation
  • Leaking Heater valve
  • Externally restricted A/C Condenser
  • Internally restricted A/C Condenser
  • Externally restricted engine cooling radiator
  • Faulty Outside Ambient  Temperature sensor
  • Faulty Pressure sensor/switch
  • Faulty Evaporator Temperature Sensor
  • Faulty electric wiring
  • Open fuses
  • Restricted A/C Cabin-filter
  • Restricted evaporator coil
  • A/C Door Actuator malfunction
  • A/C Temperature Door Actuator stuck in the heat position
  • Faulty Expansion Valve
  • Faulty Fixed Orifice Tube
  • Bad drive belt tensioner
  • Worn down a/c compressor drive belt

Why is my car AC running but not cooling?

Newer automotive air conditioner systems have the a/c compressor always operating. The a/c compressor pulley is constantly rotating but the a/c compressor output is controlled in many cases by the ECM or the PCM in the vehicle. The Powertrain control module (PCM) or Electronic controlled Module (ECM) will receive input from different sensors in the vehicle and will command a/c compressor output accordingly.

Do you need assistance with a poor a/c cooling performance ?

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ac freon recharge near me

The only accurate method to recharge an automotive a/c system that requires a critical charge is to weigh the refrigerant (Freon) into the  system using a manifold gauge set and calibrated special scale for this purpose. Recharging the a/c system by pressure, which is the method used when the system is recharged using small refrigerant can and a gauge is inaccurate, and virtually impossible to charge the system according to manufacturer specifications. Depending on the a/c system design, the pressures will be impacted by the type of compressor, metering device(Expansion Valve or Orifice tube) ,ambient temperature and humidity. Pressure controlled systems could reach pressure cycling points faster ,increasing the compressor clutch cycling and forcing the compressor to operate under higher-than-normal crankcase temperatures if the system is undercharged. Short cycling compressors will decrease the life of the compressor clutch assembly, due to more often engagement and disengagement of the clutch assembly and the compressor pulley. When the system is overcharged the evaporator will not be able to evaporate the refrigerant metered by the metering device and liquid refrigerant could reach the a/c compressor. An overcharge  system will force the a/c component working pressures to the limits and could develop leaks and cause compressor damage.

Car A/C system Recharge near me

Improperly recharged car a/c systems will increase or decrease compression ratios, negatively impacting the overall health of the a/c system. Just because the air conditioner is blowing cold air, it doesn’t mean is working according to manufacturer specifications. Modern car a/c systems design have the capability to adjust their operation even when the freon recharge is not 100% accurate. The a/c system will change compressor displacement, thermal expansion valve operation ,condenser fan speed and will force the system to get to the desired temperature set by the driver. Car a/c systems working under inaccurate freon charge will have compression ratios that will stress the compressor and shorten their life. The manufacturer calculated values of superheat and subcooling happening in the evaporator coil and condenser coil will change, making it harder for the metering device to respond to the flow of refrigerant and for the compressor to receive refrigerant oil back from the evaporator needed for internal piston lubrication. Flash gas rates will be higher at the expansion valve making the valve less efficient.

Ac freon recharge near me

You will need an AC freon recharge if the system is low or after any repair that involves opening the closed loop sealed air conditioning system is performed in your vehicle. A low freon charge could be the result of a leak in any component of the car ac system. Properly fixing a low freon condition involves more than just recharging the a/c system. If there is a leak in the system it must be fixed, otherwise the freon charge could only last couple hours or days before it is low again. Refrigerant leak and refrigerant oil leak happen together ,just at different rates. Recharging the freon in the car ac system without balancing and recharging the oil will lead to compressor failure.

Do you need a Freon recharge in your vehicle ?

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Yellow Jacket manifold gauges

Auto A/C Compressors have evolved over time and the old, fixed displacement compressor has been replaced by more efficient variable displacement compressors. Pressure controlled variable displacement compressor and Electronically Controlled Variable Displacement Compressor (ECV) react in different ways compared to fixed displacement compressors when air conditioning restrictions and other common automotive a/c faults happen. Failure to identify the type of a/c compressor in the vehicle at the beginning of the diagnostic procedure could lead to unnecessary, expensive and in most cases time consuming repairs. A restricted Thermal Expansion Valve creates Manifold gauge readings that could lead to chasing a/c system leaks, unnecessary auto a/c compressor and sensor replacement.

How do I know if my compressor or expansion valve is bad?

Manifold Gauge readings

Low side LOW        High side LOW

A restricted Thermal Expansion valve gauge readings will be different in the newer Pressure controlled variable displacement air conditioning compressor.

 When a restriction in the refrigerant flow caused by a Thermal Expansion Valve (TXV) fault happens, the Pressure controlled variable displacement compressor will try to compensate the change in refrigerant pressure from the TXV by adjusting the compressor internal control valve, and keep the compressor crankcase pressure at a value where the swash plate angle based on the low side pressure is prevented from going into the condition where you see a manifold gauge vacuum reading. The manifold gauge reading in this type of system will show Low side gauge reading low and High side gauge reading low. It could be erroneously diagnosed as a weak compressor problem.

Low Side into Vacuum         High Side LOW

A restricted Thermal Expansion Valve (TXV) gauge reading on an Electronically Controlled Variable Displacement Compressor will be different due to the logic the Powertrain Control Module uses to operate and control the a/c compressor. The PCM will receive inputs from the evaporator temperature and will command signals to the ac compressor electronic control valve to adjust pumping capacity accordingly. When the TXV fails or is restricted the evaporator temperature will increase and that increase value will be sent to the PCM which in turns will increase compressor pumping capacity to 100%.The Electronically Controlled Variable Displacement Compressor will operate similar to an old ,Fixed Displacement A/C Compressor and the Manifold Gauges will show Low Side going near 0 Psig or into a vacuum reading.

How do I know if my compressor or expansion valve is bad?

  • The type of system must be identified
  • The type of a/c compressor must be identified
  • Manifold Gauge Readings must be checked
  • PWM signals to the ECV must be inspected

Avoid unnecessary expensive repairs.

The air entering the cab is only slightly cool, and there are bubbles visible in the sight glass. there is usually about an 95% chance the restriction is expansion valve failed in the closed position related, 4% chance it is drier related and 1% chance it is somewhere else along the system or  an internal drier desiccant bag rupture leading to a/c system contamination and restricting the metering orifice of the expansion valve.

Call Us today if your A/C is experiencing this symptoms! The correct diagnostic procedure will save you TIME and Money. Auto A/C Repair LLC. offers mobile a/c inspection in Hialeah,florida.

Auto A/C noisy compressor troubleshooting chart
Compressor NoisyAC compressor internal noiseBearing worn or damagedDefective cylinder/or shaftDisassembly and replace defective parts.
Magnetic Clutch Noisy.Rattling noise when magnetic clutch is not engaged .Bearing worn or damaged.Replace bearing.
Noise from pipingPiping not secured.Piping vibrating .Pulsating noise resonates into body.Secure piping.
Noise from condenserCondenser vibration prominent.Condenser mounting stay resonating with body .Secure by inserting rubber between stay and body.
Noise produced by bracket.Rattles when touched, continuous rattling heard when operating.Bracket cracked or broken.Mounting bolts loose.ReplaceRetighten bolts.
Idler pulley noisy.Clattering noise produced. Rattles when touched.Bearing broken.Bracket Cracked or loose.ReplaceReplace or retighten.
Noisy crankshaft pulley.Rattles.Improperly installed.Replace or retighten.
Belt NoisyBelt deflection excessiveBelt side surface wornBelt wornBelt wornBelt center misalignedWorn belt causing belt slipping on pulleys and tensionerAdjust tensionAlign centerReplace belt
Noisy belt tensionerSquealing belt and/or rumbling noiseTensioner bearing or tensioner spring weakReplace belt and tensioner
*Chart provided by Denso.

Do you need assistance inspecting a noisy a/c compressor ?

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How do you test a car condenser

How do you test a car condenser ?

The best way to test a car condenser is by knowing how it should be operating correctly. You can compare the operation and determine if there are any issues with the condenser. A quick and easy test could be performed without using any special tools.

  1. Start the engine
  2. Turn the A/C on
  3. A/C set to Max Cold and Max blower operation
  4. Run the A/C for a few minutes to let the system stabilize
  5. On the engine compartment locate the condenser(It is in front of the car and looks like the radiator)
  6. Feel the temperature of the condenser coil beginning from the top of the condenser to the bottom of the condenser.
  7. A good operating condenser should be hot at the top warm on the middle of the condenser coil and cool on the bottom part of the coil surface.


Results of the condenser Test


  1. Cold spot on the condenser coil surface indicates a problem and must be corrected
  2. Hot from top to bottom condenser coil indicates a problem and must be corrected


Normal operation of an a/c condenser


  • The Hot superheated gas from the compressor enters the top of the condenser at 200 F. The condensing temperature is going to be about 30 F warmer than the outside(ambient) air.
  • The outside air temperature is 95 F. The condensing temperature is 95 F + 30 F = 125 F. The refrigerant must be cooled to 125 F (200 F – 125 F) in the first part of the condenser coil. This is call desuperheating. It is the first job of the condenser.
  • Partway through the condenser coil the superheat is removed and the refrigerant reaches the actual condensing temperature of 125 F ; liquid begins to form in the coil. Liquid will continue to form at the condensing temperature of 125 F until all the vapor has turned to 100 % liquid. This is called the Latent Heat of Condensation.
  • The liquid can now reject sensible heat and subcool to below the 125 F condensing temperature. Any liquid below 125 F condensing temperature is referred to as a subcooled liquid.
  • The liquid in the bottom of the condenser draining into the receiver or expansion device depending on the type of system may cool to 110 F. This would give the liquid 15 F(125 F – 110 F) of subcooling.


Impact of debris and damage of the car condenser and temperature differential.


All air-cooled condensers do not have the same exact 30 F relationship with the ambient air. It is good practice to determine and record the temperature relationship between the air and refrigerant at start-up time. Then if the relationship were to change, you would suspect trouble, such as a dirty condenser, system contaminated or an overcharge of refrigerant.

A well-maintained clean condenser will have a close 30 F or even lower temperature relationship with the ambient air, compared with a road debris restricted ac condenser. The efficiency of the condenser will vary according to the condenser design, size and quality of the materials used for its construction. The operation of the a/c condenser depends greatly on the flow speed and volume of air going through its fins to accelerate the heat exchange between the refrigerant and the ambient air.


Do you need assistance checking your car ac condenser ?

Call Auto A/C Repair LLC. Today ! Auto A/C Repair LLC. provides car ac repairs on site service in your area. ASE certified mechanics can service your automotive ac system at your home or office. A/C specialist near you will take care of your air conditioning system.


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ac temperature out of the vents

How the a/c should be operating in order to cool down the interior of your car

Check inside the vehicle:

  • The A/C climate control should be set to Max Cold Position.
  • A/C Climate control set button On.
  • Recirculation/fresh air mode set to recirculate.
  • Engine temperature should be in the normal range (not overheating)
  • Outside ambient temperature should be sensing outside actual ambient temperature.(Ambient temperature should be above 37 F )
  • Engine RPM’s should in the normal everyday range.
  • With the A/C  blower on Max, the mass of air coming out from the vents should be strong.
  • Cabin air Filter should be clean.
  • A/C evaporator coil should be free from debris and leaks.

Check the engine compartment :

  • The front of the vehicle should be free from any road debris.
  • The radiator and A/C condenser should be free from leaves, bugs or dirt.
  • With the A/C system ON the radiator/condenser fan assembly should be operating.
  • The Drive belt should be running all the accessories and in good condition.
  • The A/C compressor CLUTCH should be engaged with A/C ON.
  • The A/C compressor ECV should be modulating the hvac compressor output for max cold.
  • All A/C lines and hoses should be free from dye, oil ,ice or damage.
  • The A/C system should be properly charged with exact amount of refrigerant specified by the manufacturer.
  • Hvac box drain tube should be draining water from underneath the vehicle.



Learn More…

automotive ac compressor and refrigerant lines

Sun Load or Ambient Light Sensor

The sun load sensor function as an input for the module in charge of automatically controlling the headlight operation and air conditioning system control module.

How to test the Sun Load or Ambient Light Sensor ?

A bright LED light may be used to artificially force the sensor  to adjust for light intensity and angle. With the headlights in the automatic setting position, we should see the running lights coming on and off and the automatic climate control adjusting the air temperature out of the vents. Exposing the sensor photocell to the strong led light will increase the current flow from the sun load sensor while  covering the sensor photocell will decrease the current flow signal to the hvac control module and headlight control module. With a scan tool connected to the vehicle or a multimeter we should be able to see these variations in voltage when the sensor is operating properly. The most common voltage range is between zero and five volts, but is always a good idea to compare the readings against manufacturer specs.

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Nissan vehicle interior. Sun load sensor.

How does the sun load sensor in my car work?

Varying amounts of exposure to sunlight will modify its electrical return signal to the programmer to adjust system output toward cooler air; less sunlight will cause the programmer to adjust system output toward warmer air. Some multizone climate control systems have more than one sun load sensor.

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