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, you’re 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.
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What sound does a bad AC compressor make?

A/C operation, normal noises.

Normal noises include the sounds of A/C compressor clutch engagement, the blower motor, moving blend air and mode doors, and pressure equalization after vehicle is shut down.

Noises that could indicate the need fora/c compressor service or replacement include:

  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

Why is my AC making a weird noise?

Banging noise: If liquid refrigerant enters the compressor, a thumping, banging noise will result.

Knocking noise: Heavy knocking compressor noises come from refrigerant system blockage, incorrect pressures, or internal damage.

Growling noise with compressor disengaged: A worn compressor pulley bearing or clutch bearing will cause a growling noise.

Growling noise with the compressor engaged: A/C compressor internal bearings damage.

Squealing noise: A loose, dry, or worn A/C compressor belt will cause squealing noise. This noise will be worse during acceleration.

Worn or dry blower motor bearings may cause a squealing noise when the blower motor is running

Rattling noise: A loose or worn clutch hub or loose compressor mountings bolt will also cause rattling noise from the compressor.

Knocking noises: This type of noise from the compressor usually indicates internal damage, especially on piston-type compressors. Always check the compressor mounting and brackets before condemning the compressor for noise.

A loose mounting can cause knocking noises from the compressor area that may be mistaken for internal compressor noise.

Grinding noise: When car accessories pulley bearings are failing, they can make this kind of noise.

What are the Symptoms of a Bad or Failing Ambient Temperature Sensor?

Diagnosing a bad or failing Ambient Temperature Sensor.

  1. The air conditioning  “AUTO MODE “ won’t  work
  2. Inconsistent cooling or not cooling at all.
  3. A/C compressor inoperative
  4. Incorrect reading on temperature gauge. Usually a default negative temperature.


The most common variable resistor is a thermistor.Thermistors change resistance based on temperature changes. There are two different styles of thermistor: NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient).The difference is in how they react to temperature changes.

As temperature rise:

-PTC thermistor-resistance increases

-NTC Thermistor-resistance decreases

The NTC thermistor is more common than the PTC thermistor.

Here are some examples of thermistor in automotive circuits:

  • Engine temperature sensor
  • Evaporator temperature sensor
  • Ambient temperature sensors-In-car and outside sensors
  • A/C High Side Refrigerant Temperature Sensors
  • A/C Low Side Refrigerant Temperature Sensors
  • Sun Load Sensors (Not all sun load sensors are thermistor some are photoresistors.A photoresistor measures the amount of light hitting it .As the light intensity increases , sensor resistance decreases. That’s the why a photo resistor works so well as a sun load sensor. Some manufacturers use a photodiode. A photodiode works in a manner similar to the photoresistor.
What does the ambient temperature sensor do?

It prevents the compressor from engaging when ambient temperatures get too low. The oil that resides inside of a compressor can get very cold during the winter months. If the compressor’s clutch is energized while the oil is cold and thick, improper compressor-lubrication would result.

Where the ambient temperature sensor is usually mounted?


Mounted to the radiator support, in front of the condenser where it can sense outside temperatures without being affected by engine heat.

How does ambient temp sensor work?

A lot of air conditioning systems are supposed to run when you turn the defroster on, to help remove moisture from the air. But when outside temperatures are very low refrigerant oils won’t flow and lubricate the system properly.

The ambient temperature sensor prevents the compressor from running when it’s too cold for the system to work safely. These switches open when the temperature drops below a preset temperature,usually below 32° F

What is the purpose of the cycling switch in a cycling clutch system?

The A/C cycling switch cycles the compressor clutch on and off to maintain evaporator temperatures above freezing.

Where is the clutch cycling switch located?

Thermostatic cycling switch: Some vehicles mount it in the engine compartment, near the evaporator case. Others mount theirs under the dashboard near the evaporator.

Pressure cycling switch: The A/C pressure cycling switch is located in the low-side. Some vehicles mount theirs on the accumulator, others on the lines.

Some vehicles use a temperature-controlled cycling clutch switch to maintain evaporator temperatures. The switch opens or closes the circuit to the compressor clutch, based on evaporator temperature. The switch has a temperature sensing bulb that sits on the evaporator or along the evaporator outlet line.

The bulb is filled with a gas or refrigerant similar to one in the system. If the evaporator core gets too cold, the pressure of the refrigerant in the sensing bulb drops. That allows the contacts in the cycling clutch switch to open, which releases the compressor clutch and stops the compressor.

As soon as the compressor stops turning, the pressures in the system begin to equalize. The evaporator pressure increases and warms up. That warms the sensing bulb enough to let the cycling clutch switch close. The compressor clutch engages, and the cycle begins again.

Pressure controls maintain evaporator temperature. 

Cycling the compressor clutch based on evaporator temperature is just one way to control evaporator temperature. Since refrigerant temperature can be controlled by adjusting the pressure, some manufacturers use a pressure switch on the accumulator to monitor evaporator pressure and cycle the compressor clutch.

Low-side refrigerant pressure sits on one side of a diaphragm, spring pressure on the other. When refrigerant pressure exceeds a predetermined value about 45 PSI (310 kpa) it overcomes the spring pressure, forcing a set of electrical contacts to complete the circuit, and energizing the compressor clutch.

As the compressor runs, low-side pressure drops. When low-side pressures drop below about 23 PSI (159 kpa), the spring tension overcomes refrigerant pressure; the contacts in the switch open, shutting the compressor clutch off. Pressures rise, and the cycle begins again.

Electronic cycling clutch switch

Electronic cycling switch monitors evaporator temperature, and turns the compressor on and off to maintain evaporator temperatures over 32° F (0ºC).

How do I know if my AC cycling switch is bad?

The AC system is not blowing as cold as it used to, that may be a sign that the switch has failed, or is beginning to fail

Your AC system will completely cease to blow cold air without the cycling switch to activate the compressor’s clutch.

The A/C compressor cycles on and off too often and out of pressure specifications. You can hear the clicking noise of the A/C compressor clutch engaging and disengaging.

How do I know if my AC clutch relay is bad?

What is a clutch relay?

A relay is a device that allows you to control high amperage circuit from low amperage circuit.

Automotive switches and electronics are wired to relays since they aren’t designed to handle the arcing and high current demand required in some circuits.

How a relay works

Every relay has at least two circuits running through it: a low-amperage, or CONTROL circuit, and a high amperage, or load circuit.

When you energize a relay, you’re actually energizing the control circuit. This energizes an electromagnet in the relay, which opens or closes a set of contacts. The contacts are part of the load circuit. When the contacts close, they complete the high amperage circuit, allowing current to flow.

Different types of relays

Relays can be normally-open (NO), normally-closed (NC) or can have dual contacts.

Normally-open contact relays have one set of contacts that remain open when the relay control circuit is de-energized. When you energize the relay, the contacts close, completing the high amperage circuit.

Normally-closed contact relays work the opposite way: The contacts are closed when the relay is de-energized. Energizing the control circuit in the relay opens the contacts, shutting off the current in the load circuit.

Dual-contact relays have one set of normally-open contacts, and one set of normally-closed contacts. When the relay is de-energized, current flows through the normally-closed contacts. When you energize the relay, the normally-closed contacts open, and the normally-open contacts close. Now current flows through the normal-open contacts.


Most mini-relays have four or five terminals. The two small terminals(often specified as 85 and 86) are used to energize the coil that creates the magnetic attraction necessary to cause a connection between the high amperage switch contacts.Two other terminals make the high amperage-amperage power in (terminal 30) and power out (terminal 87) connection. Sometimes a fifth terminal (marked 87a) is used as a normally closed (NC) contact, as opposed to 87 being normally-open (NO), which closes when the relay energizes.

Solid state relays

Some manufacturers use solid-state relays in different areas of  the car. The operation of these devices is much like an electronic fuel injector. These components can be totally off or tally on, like regular relays. What differentiates them is their ability to be turned on to a certain percentage with a pulse-width modulated signal. The advantage of these devices is that they can control the current flow to the output device, resulting in a variable speed device.

A scan tool is necessary to troubleshoot these solid-state relays. The scan tool can retrieve trouble codes as well as perform output tests on these circuits during the troubleshooting process.

How do I know if my AC clutch relay is bad?

When testing these relays:

  1. Unplug the relay
  2. Measure for continuity between pins 30 and 87a.There should be less than 1ohm resistance.
  3. Measure for continuity between pins 30 and 87.There shouldn’t be any continuity between these terminals
  4. Apply power (12volts) to pin 86 and ground to pin 85.The relay should click.
  5. Measure for continuity between pins 30 and 87a.There shouldn’t be any continuity between these terminals.
  6. Measure for continuity between pins 30 and 87.There should be less than 1ohm resistance between these terminals.
What are the symptoms of a bad relay?

Signs of a Bad or Failing AC Compressor Relay

The AC compressor will not have power and the AC system will not function.

AC compressor intermittent operation causing weakened or intermittent cooling performance.

If you are experiencing issues with your AC system and suspect that your AC relay has either failed or is beginning to fail, we recommend having it diagnosed by a professional technician.

How do you diagnose an air conditioner

Air Flow

No air flow

  1. Inspect blower motor
  2. Inspect blower motor resistor
  3. Inspect fuse
  4. Inspect A/C climate control
  5. Inspect connectors
  6. Inspect harness
  7. Inspect hvac box for


No cooling

  1. Inspect A/C switch
  2. Check refrigerant level
  3. Inspect clutch relay
  4. Inspect PCM/BCM/ECM
  5. Inspect A/C pressure switch
  6. Inspect compressor clutch coil
  7. Inspect compressor clutch
  8. Inspect compressor clutch air gap
  9. Inspect condenser
  10. Inspect condenser fan
  11. Inspect radiator fan
  12. Inspect evaporator temperature control devices
  13. Inspect temperature sensors control devices
  14. Inspect climate control
  15. Inspect in cabin temperature sensors
  16. Inspect sun load sensors
  17. Inspect power steering pressure sensor

Bad Smell

  1. Check cabin air filter
  2. Check evaporator core
  3. Check hvac box drain tube
  4. Check re-circulation air door /actuator
  5. Check hvac box seals


Clicking noise

  1. Check A/C clutch
  2. Inspect A/C clutch relay
  3. Inspect cycling switch
  4. Inspect refrigerant level
  5. Inspect evaporator temperature sensor


  1. Check drive belt
  2. Check belt tensioner
  3. Check compressor for seizing


  1. Check compressor
  2. Check compressor clutch
Other helpful tips

Replace the receiver driver with every A/C service.

Replace cabin air filter annually

Ensure that service valve caps are in place at every A/C service.

Auto A/C Sight Glass diagnosis.


A sight glass is a transparent glass tube or window installed in a tank or boiler system that allows an observer to view what is happening inside the system.

The refrigerant sight glass is normally located anywhere liquid flow exists and anywhere it can serve a purpose. When it is installed just prior to the expansion device, the technician can be assured that a solid column of liquid is reaching the device. When it is installed at the condensing unit, it can help with troubleshooting.

Sight glasses come in two basic styles: plain and with a moisture indicator. The plain sight glass is used to observe the refrigerant as it moves along the line. The sight glass with a moisture indicator can tell what the moisture content is in the system. It has a small element in it that changes color when moisture is present.

What you see in the sight glass can help you diagnose system malfunctions. It is strongly suggested that you do not use the sight glass as the only means of diagnosis. Also, do not use the sight glass to diagnose R134a systems.

If the sight glass is clear, one of three conditions can exist: the system is completely empty, the system is full, or the system is overcharged. If there is foam, the charge is low, but if there are only a couple of bubbles, it is probably Ok. few bubbles when the compressor cycles on is normal. Oil streaks in the sight glass usually indicate a low charge and that the compressor is pumping oil from its sump. If the sight glass is cloudy, the desiccant bag has probably burst.

If an R134a system has a sight glass, do not use it or try to perform diagnosis, as it is normal to observe bubbles in this type of system.



System Ok

System overcharged

System empties (No refrigerant)


System low on refrigerant

System contaminated with air


System may be low on refrigerant

Oil may streak as oil circulates


Desiccant breakdown 

Contaminated system

Can I drive my car with a bad AC compressor?

Will a bad AC compressor affect the engine?

A bad compressor could affect the engine in your car. If your compressor’s pulley bearing goes bad, your engine can stall due to the stuck compressor or the serpentine belt may break affecting all the accessories moved by the serpentine belt.

Clutchless variable displacement piston compressors and compressor lock up. 

Clutchless variable displacement compressors have extra protection in case the compressor seizes.In the event  a compressor failure occurs the bridges on the clutch assembly will break and only the pulley will keep running, allowing the engine to keep running.

Does engine coolant affect ac performance?

High coolant temperature affects A/C performance.

The engine cooling system has an indirect influence on the performance of the A/C system. High under hood temperatures can be the cause of poor A/C output. 

Always verify correct operation of:

  • Engine coolant level and condition
  • Low coolant will cause high under hood temperatures
  • Does the cooling system need flushing?
  • Has the vehicle followed the manufacturer’s service intervals for flushing?
  • Does it have the correct coolant in it?

  • Thermostat
  • Has the thermostat ever been replaced?
  • Is it stuck, not closing or opening all the way?

  • Radiator
  • Is the radiator plugged internally or externally?
  • Are there any signs of leaks?

  • Water pump
  • Is the mechanical pump circulating the coolant properly?
  • Are electric pumps working properly?
  • Should it be replaced when servicing the timing belt?
  • Belts,tensioners,and pulleys
  • Check for proper belt tension and verify the belt is not slipping
  • Check tensioner alignment

Why did my car AC stop blowing air ?

My car A/C stop blowing air from the vents.

Common reasons for this to happen:

  • A/C blower motor circuit blown fuse
  • Bad blower motor resistor
  • Blower motor shorted
  • Bad blower motor control switch
  • Poor ground connection
  • Poor blower motor connections

Ram air flowing through the evaporator does not provide enough air flow inside the vehicle for cooling purposes. So, a blower is used to force the air along. An electric motor spins a fan, forcing the air into ducts, which direct it to the particular vent selected by the operator.

If the blower motor gets full voltage, it will run at high speed, but that is not always desirable. Therefore resistors are used to cut the speed down. The fan switch directs the current flow through one or more resistors to achieve the slow and medium speeds.

Why did my car AC suddenly stop working?

The most common causes of broken air conditioning are:

Leaks, compressor issues, electrical / electronic faults.

Compressor and electrical / electronic faults.

Inputs that may affect A/C clutch operation include (but are not limited to):

  1. A/C system pressure
  2. Engine speed
  3. Throttle position
  4. Engine coolant temperature
  5. Intake air temperature
  6. Power steering pressure

If these sensor and switch values are either above or below the programmed operating range, the compressor clutch may not engage

Depending on the vehicle, additional items that may affect compressor operation could include:

  1. A/C mode switch/actuator
  2. Body control module
  3. High and low pressure cut-out switches
  4. Compressor clutch cycling switch
  5. Refrigerant pressure transducer

Refrigerant leaks .

There are two types of refrigerant leaks in the automotive air conditioning system: Active leaks and Passive leaks.

  1. The active refrigerant leak is a continuous leak. It doesn’t matter if the engine or ac system in your car is off or on hot or cold the refrigerant continuously leaks out
  2. The passive refrigerant leak is a type of leak the intermittently occurs. They are really hard to find, because technicians should recreate the same conditions of pressure, temperature or vibration for the leak to happen.