Repairing an Air Conditioning Compressor

If you have seen my posts in the Citroen club area, you will know I have had problems with my aircon and have been loosing refrigerant from my aircon system. An investigation reviled an oil leak coming from a seal on the compressor. Well the old saying is where there is smoke there is fire. In this case, where there is oil, there is a leak.
This looks like a bad seal between the 'nose piece' and the compressor body.
Removing the compressor was quite easy. De-tension and remove the accessory drive belt. Remove the suction and discharge lines (just one nut each). Remove the four bolts holding the compressor onto the mounting bracket.

I didn't want to disturb the shaft seal on the compressor as it didn't seem to be leaking from there, only from the seal between the nose piece and the compressor body. So I didn't pull the pulley and clutch off the nose assembly.The shaft seal is very delicate and requires a special tool to install it onto the input shaft.
Fortunately it was easy to remove the bolts holding the nose piece on.
Also fortunately the seal is an oring. Unfortunately a replacement could not be found. The aircon system, just sitting there, in the car, is at about 140 PSI. So this seal has to survive at least that. The cylinder head seal (in the compressor) has to withstand more than 250 PSI and is typically made of metal!
Also unfortunately, the compressor is showing signs of corrosion and as predicted (in my other post) there is a lack of oil in the casing.
The photo makes the corrosion look worse than it really is. Actually, most of the black smudges you see is a greasy/sticky dark residue. What oil there is in the compressor is actually relatively clean. The black 'stuff' is obviously wear contaminants from the compressor but why it's a sticky smudge and not in the oil is a mystery!

Synthetic gases used in aircon systems (like R134A) are Fluorocarbons. If the gas is exposed to moisture in a sealed system, they form acids. So aircon systems are purged of moisture by vacuuming the system down and having descant 'driers' in the system.
Unfortunately this system has had moisture ingress, for one reason or another and that has caused corrosion on most of the components. So far it is just light corrosion and discolouration. the important bits like the pistons bores and reed valves all look OK. If the corrosion got bad, small flakes could circulate around the compressor and cause damage. There is a filter in the receiver/drier at the end of the condenser. This will filter large particles but very fine partials may find their way around the complete system.
I am not too concerned about the level of corrosion as it will not effect the longevity or performance as long as it doesn't get worse.
Under normal circumstances I would have stripped the compressor down and cleaned it and replaced the seals BUT obtaining a seal kit for a Sanden SD6V12 was going to take some finding and time. It is bloody hot here at the moment and I don't want to be with out the aircon!
However the failure of the seal seemed to be caused by corrosion under the oring on the mating surfaces and not the oring itself.
I used a plastic scourer and PAG oil (aircon lubricating oil) on the surfaces to clean them up as best as I could.
The oring seemed serviceable and when installed, was higher than the groove that it sat in. So the leakage didn't seem to be from a bad oring.

You will notice from the previous photos that the pistons are connected to the swash plate by little connecting rods on ball-and-socket joints. Putting the compressor back together was like putting a dead octopus into a bottle, tentacles first! I'll spare you the gory details and the four letter words but I got the housings back together and bolted up.

Now there needs to be an amount of oil in the total system. under normal conditions there is some oil in the rest of the system and some oil in the compressor. As the refrigerant gas leaked out, so did the oil but how much leaked out!!?? The entire system takes 135ml. However there was very little oil in the compressor. Does this mean that all the oil worked it's way around the system, into the compressor then out the leak? If this was done professionally they would flush the system to get all the residual oil out and then fill the compressor up with 135ml of oil. However I will have to guess the amount of oil to put into the compressor. Now if you use too much oil, the oil will displace refrigerant and reduce the cooling capacity of the system. Too little oil and the compressor will be noisy and it will reduce the compressors life span.
So I guessed 100ml to put into the compressor. There is a bung on the top of the compressor to install oil.

Putting the compressor back onto the engine was just as easy as taking it off.

FYI. This compressor has 6 small pistons which are connected to a swash or 'wobble' plate that cause the pistons to go in and out (in turn) as the compressor shaft rotates. the pistons draw the refrigerant gas into the piston chamber and compress it and then send the compressed gas out to the condenser (The radiator-like device at the front of the car). This compressor is a variable capacity type. Basically the amount of 'wobble' in the wobble plate is determined by the speed of the compressor. At low speeds there is maximum wobble and therefore maximum piston stroke. At high speeds less wobble and less stroke of the pistons. Effectively that means that the compressor is 'pumping' about the same amount of refrigerant irrespective of the speed of the motor.

If you are game enough to repair the compressor the seal kits are as follows:
Shaft seal Santech MT2045 but you will need a shaft seal installation tool to go over the input shaft during installation.
Gasket set Santech MT2217.
They can be found on Ebay and other places if you search the internet.
At least until 2009, the C3's had a Sanden SD6V12 model 1450 compressor. The above kits will fit this compressor.
The replacement oil is a PAG100 oil (various manufacturers). The specified oil is Sanden SP20.