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 for a/c compressor service or replacement include:
Growling noise with compressor disengaged
Growling noise with compressor engaged
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.
Diagnosing a bad or failing Ambient Temperature Sensor.
The air conditioning “AUTO MODE “ won’t work
Inconsistent cooling or not cooling at all.
A/C compressor inoperative
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
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.
Inputs that may affect A/C clutch operation include (but are not limited
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:
and low pressure cut-out switches
clutch cycling switch
Refrigerant leaks .
There are two types of refrigerant leaks in the automotive
air conditioning system: Active leaks and Passive leaks.
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
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.
The receiver drier is a storage tank for the liquid refrigerant from the condenser. It also contains a bag of desiccant.
The purpose of the desiccant is to absorb any moisture that might enter the system during assembly or service. The receiver drier is often neglected when the air conditioning system is serviced or repaired.Failure to replace it can lead to poor system performance or replacement part failure.
When should I change my AC filter drier?
It is recommended that the receiver drier and /or its desiccant be changed whenever a component is replaced, the system has lost the refrigerant charge, or the system has been open to the atmosphere for any length of time.
AC receiver drier refrigerant flow restriction.
If the receiver-drier outlet is colder than the inlet, this unit is restricted and should be changed to restore efficient and proper system operation.