car air conditioning system

auto air compressor

Auto Air Conditioning Compressor.

What causes a 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 piston’s 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 car’s 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 ?C /113 ?F (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 C / 60.8 F and the difference between right and left may not be greater than 2 C / F.

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 F/32 C 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.