Tag: compressor oil balancing

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) - 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.


AC Compressor Repair.

For an ac compressor repair we need not only to repair the symptom, but the cause too.

The a/c compressor is considered the heart of the air conditioning system. It is a pump that can be driven by a serpentine or V belt, an electric motor or in some cases both. There are 3 common compressor designs in use today, they are:

  1. Reciprocating piston type compressor.
  2. The Rotary vane type compressor.
  3. The Scroll type compressor.

The ac compressor should last for the entire life of the vehicle. The automotive ac compressor could fail because of age, a design or construction defect during manufacturing or because something in the air conditioning system is not working properly and is putting excessive stress on the compressor.

Before replacing or servicing any ac compressor we should investigate what was the cause of the failure, because the chances of damaging the new compressor are pretty high if we dont correct the cause.

How to properly diagnose a faulty a/c compressor clutch coil in your car?

If a voltage of 12 DC volts or greater is present on the clutch coil but the clutch isnt engaging it doesnt necessarily mean that the clutch coil is bad. A compressor clutch can also fail from mechanical problems, such as an excessive air gap between the pressure plate and rotor, or oil on either of these components. A/C compressor clutch failures are usually a symptom of another problem in the air conditioning system. If the problem isnt diagnosed and repaired, another ac compressor clutch failure will occur.

Some common problems automotive a/c compressors may experience.

1-High head pressures, due to:

1.1-Overcharged ac systems.

1.2-Condenser fan not working at all or working not efficiently enough.

1.3-Clogged up with road debris, condenser core.

1.4-Contaminated a/c systems, with non-condensable gases.

2-Frequent clutch cycling due to:

2.1-Low refrigerant charge.

2.2-Faulty cycling switch.

3-Lack of lubrication or incorrect type and oil viscosity.

4-High resistance in clutch ground circuit.

5-Compressor bearing contaminated with other engine fluids (coolant,power steeringetc) 

What is the cause of an ac compressor clutch not engaging?

The cause of an ac compressor clutch not engaging could be:

 1-Electric or electronic fault of any of the compressor control devices or ac compressor circuit protection device.

 2-Faulty or wrong signal input to the BCM or PCM.

 3-Faulty PCM or BCM not sending the output signal to the compressor control device(ac compressor relay).

 4-A/C compressor clutch excessive air gap.

 5-A/C system too low on refrigerant charge due leakage in the air conditioning system.

6-Compressor clutch coil winding open.

7-A/C head control set switch damage or entire a/c control set damaged. 

A defective clutch may be replaced; however, the cause of the failure should be investigated to avoid a repeat failure.It may be less risky and more cost effective to replace the complete compressor if the condition of the compressor is suspected due to age or mileage.

On variable displacement electronically or pressure controlled compressor, the valve that controls the ac compressor crankcase pressure may be faulty and the system will perform poorly or wont cool at all.

How much does it cost to fix an AC compressor?

The cost to repair an ac compressor will depend on the make, model and year of the car. There is a really big difference in terms of time and cost between replacement of the whole clutch assembly  or the entire compressor.The labor only for an ac compressor can range from $ 285.00 to $ 500.00.The price of the compressor will depend on :

-The type of compressor.

-It could be piston type fixed displacement compressor

-Pressure controlled variable displacement compressor

-Electronically controlled variable displacement compressor

-Scroll compressor

-Vane compressor

-Completely electric compressors for hybrid or electric vehicles.

The a/c compressor could be: a rebuilt or used compressor a new aftermarket or OEM (Original Equipment Manufacturer).There will be differences in terms of quality , warranty length and price according to which one of this options we choose  when buying an a/c compressor. The ac compressor price range could be from $200.00 to $ 800.00.

What are the symptoms of a bad AC compressor?

1-No cold air from the vents.

2-Clicking sound from under the engine.(Compressor clutch engaging and disengaging)

3-AC not working.

4-Noise under the engine with the a/c climate control on.

5-Burned rubber smell coming out from the engine compartment.

6-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.

Can an AC 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 or a rebuilt one. It may seem you are saving some money, but we think that in the long run buying a new compressor is always the best option.

Can I drive my car with a bad AC compressor?

The AC compressor pulley is a free spinning pulley that has a clutch on it. It is designed in such a way that during catastrophic compressor failure and compressor crankshaft lock-up or damage the pulley will be able to rotate freely on its internal bearing and the car could be taken to a safe place for service.

A/C compressor complex control system.

Different inputs Volkswagen uses to reduce compressor output or turn it off:

  1. High pressure > 464 psi
  2. Blower voltage < 3 volts
  3. Low pressure < 29 psi
  4. Engine start < 4 sec
  5. Econ mode
  6. Blower stage 0
  7. Outside temperature < 37.4 F
  8. Engine temperature > 244.4 F
  9. Engine control unit kick down coolant fan.
  10. Evaporator temperature
  11. Low or high vehicle battery voltage
  12. Faulty signal
  13. Pressure sensor fault
  14. RPM > 3000 > 5 sec
  15. Vehicle speed <10 mph
  16. Green mode
  17. Power consumption of compressor

How to add oil to a compressor?

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.