How to fit your car air con compressor pump

We get asked many times, how do you fit the car air conditioning compressor (otherwise known as the aircon pump). Is there a right way? Is there a correct procedure?

Many garages simply remove the old unit, and bolt on the new one, regas the car and hope it works. Problem is it might, but after a few weeks it stops and the garage blames the compressor. You CANNOT just remove the old unit and replace it. You have to find out why the old unit failed, clean the system with a proper flushing solution to remove any debris, or that debris finds its way into the new compressor, and you must add the correct quantity of oil, of the right type.

If you don't do these things, you run the risk of the compressor failing again, and yet another expensive replacement, recharge, labour etc through no fault of the unit, but just of the people fitting it. We get calls every week from customers who have had a new compressor fitted and then complain it's not working. 99% of the time it is down to it not being fitted correctly, or the initial fault has not been diagnosed properly.

When a compressor fails internally, tinny particles mix with the oil that circulates around the entire A/C system. This contaminated oil must be flushed out of the A/C components that will be re-used. Blowing air through the components does not remove the contaminated oil.

When a compressor fails due to internal failure as evidenced by poor pumping or the shaft locked up or uneven turning, tiny particles mix with the oil that circulates around the entire A/C system so contamination is circulated in the system both in the forward and reverse direction and must be flushed with proper flushing fluid. Contamination is circulated in the forward direction until the compressor is disengaged and then the rapid equalisation of pressures causes contamination to flow in reverse back up the suction line to the evaporator. The warranty and reliability of a replacement compressor depends upon returning the A/C system to like new conditions in terms of cleanliness and proper operation of the system.

Compressor Fitting Instructions

1. Visually inspect the new unit for any damage ensuring that all fixing points are complete and that the pulley moves freely. Visually check the replacement unit against the item on the car to ensure they are the same (before removing unit).
2. Once unit is removed) Check new compressor against old compressor ensuring units are the same and that the pulleys align correctly, in certain systems it is possible that different makes of compressors are interchangeable they may look slightly different however upon matching the fixing points, clutch and plug should all match.
3. Completely flush the system to remove any debris from the old compressor that may contaminate the new one. This is done with a flushing solution, and is not the same thing as simply vacuuming the system or flushing with nitrogen.You will need to check the compressor and ensure the correct charge/type of oil. (replacement compressors do not always come with oil charge!). It is VITAL to ensure you add the correct volume of oil, and it is of the right type. Too much or too little and the compressor will fail. We provide a flushing kit if needed.
4. If you are not flushing the system (and the system is completely clean with no debris) you can drain the old compressor of oil.
   • Remove the oil plug from the failed compressor and drain as much oil as possible from the suction and discharge ports and from the crankcase into a suitable container. Drain for about 3 minutes while turning the front shaft nut one half turn every minute. Also slightly tilt the compressor back and forth a few times to help the oil reach the oil drain hole.
   • Measure and record the amount of oil drained from the compressor.
   • Drain oil from the new compressor following.
   • Replace some of the new oil back into the new compressor in an amount equal measurement taken.
   • Re-install oil plug. The aluminium seal seat and O-ring must be clean and not damaged. Torque to 11-15 ft•lb (15-20 N•m, 150-200 kgf•cm). Be careful not to cross thread the oil plug.
   • You must not over oil charge the system!
5. When fitted to the vehicle rotate the front hub of the compressor by hand 10 times clockwise/anti-clockwise to ensure that the oil is distributed.
6. Upon installation in certain circumstances it may be necessary to swap the fitting plate from the existing compressor to the new unit (this is the plate where the hoses go into).
7. On remanufactured compressors it may be necessary to swap the wire plug from the old unit to the replacement unit.
8. After installing ensure that the last component installed is the receiver drier/accumulator, and then evacuate the system for 30 minutes minimum prior to leak testing. Ensure no leaks are present, check system operating pressures and temperatures ensure that the radiator/condenser fans work correctly. You must ensure that the high side pressures are not excessive and that the low side is not too low. When using Automatic / semi Automatic  charging stations they DO NOT add correct oil charge to compressor this must be completed prior to compressor installation.
9. When fitting clutch less type compressors it is sometimes necessary to have the fault codes removed from the computer memory otherwise the compressor may not receive the correct feed and will not pump. YOU MUST ALWAYS FLUSH THE SYSTEMS TO REMOVE EXCESS OIL. Should the compressor not pump immediately then remove control valve and sump drain plug, then blow through the control valve port ensuring that air is felt at the drain plug, this action ensures that the refrigerant bleed from the control valve to the swash plate is free and will then allow for the correct control valve operation.

Please remember that compressors do not just fail, there will be a reason why it originally failed and you MUST find and rectify this underlying fault otherwise the replacement WILL fail.

Please ensure that whoever is fitting the compressor is an A/C specialist, and not a local garage that does a bit of aircon on the side, you need to use someone that knows what they are doing, that are qualified, and trained in automotive air conditioning, for example Cool Car Air Conditioning Specialists.