944 A/C Condenser Leak

[Bill]

Like Dr Bob, I too have learned many lessons during my relationship with the Porsche cars.

If I were pressed as to what is my number 1 lesson would be, it would have to be “do not use aftermarket parts” After much angst on fitment and durability, I now only use Porsche parts. With this mantra, the disillusionment that I had towards my car continually breaking has changed to the joy received driving it.

Fix it once, fix it right and you will be rewarded with a joy filled driving experience.

[Chico Jon]

Is it always necessary to flush the whole ac system when changing out the compressor? From what I can tell mine didn't seize. It just is leaking from the compressor. I've read that flushing will remove all old oil from the system also. I'm converting to 134, adding a new expansion valve, condenser, compressor and drier. Also, if you are flushing is regular compressed air okay? I'm in Northern CA. with low humidity.

[Tom]

Is it always necessary to flush the whole ac system when changing out the compressor? From what I can tell mine didn't seize. It just is leaking from the compressor. I've read that flushing will remove all old oil from the system also. I'm converting to 134, adding a new expansion valve, condenser, compressor and drier. Also, if you are flushing is regular compressed air okay? I'm in Northern CA. with low humidity.

I did not flush my system (in any meaningful way anyway) and it was fine. Like you, my compressor was just old, not spitting up shrapnel. You'll need to add a couple ounces of oil to account for the new condenser.

[dr bob]

I'm with Tom on this. My car came with factory-original AC leaks, and got the R-134a conversion after eight months and three R12 'recharges" after it came to me (at about 8 years old and less than 17k miles on the odometer at that point). For that I did an aerosol-can 'flush' of the condenser and evaporator. I'd removed the drier but not the expansion valve, stuck a piece of hose in place of the drier, and 'flushed from compressor out connection to a bucket under the inlet/suction line. Efficient? Sort of I guess, as it did a decent job of getting the old mineral oil out, my primary goal. Replaced o-rings, a few hoses, new drier. Evacuated for a day to make sure any remaining flush solvent and any moisture was removed. I decided to use polyolester oil on the chance there were any bits of mineral oil hiding, vs. the PAG that Denso recommends/supplies.

The 928 has rear AC, and that was a separate flush and leak-fix exercise. The front system is very conventional, and really needed nothing beyond what any mere-mortal production car needs. If you are 'converting' and don't plan on replacing your old hoses with modern "barrier" versions for the R-134a, I'd hesitate to recommend a significant solvent flush through those hoses. The old oil soaks and sort-of seals the liner in the hose. Removing that with the flush chems increases the amount of R-134a that will pass through the hose walls.

It was definitely worth the conversion, should anyone have doubts.

[Chico Jon]

I'm with Tom on this. My car came with factory-original AC leaks, and got the R-134a conversion after eight months and three R12 'recharges" after it came to me (at about 8 years old and less than 17k miles on the odometer at that point). For that I did an aerosol-can 'flush' of the condenser and evaporator. I'd removed the drier but not the expansion valve, stuck a piece of hose in place of the drier, and 'flushed from compressor out connection to a bucket under the inlet/suction line. Efficient? Sort of I guess, as it did a decent job of getting the old mineral oil out, my primary goal. Replaced o-rings, a few hoses, new drier. Evacuated for a day to make sure any remaining flush solvent and any moisture was removed. I decided to use polyolester oil on the chance there were any bits of mineral oil hiding, vs. the PAG that Denso recommends/supplies.

The 928 has rear AC, and that was a separate flush and leak-fix exercise. The front system is very conventional, and really needed nothing beyond what any mere-mortal production car needs. If you are 'converting' and don't plan on replacing your old hoses with modern "barrier" versions for the R-134a, I'd hesitate to recommend a significant solvent flush through those hoses. The old oil soaks and sort-of seals the liner in the hose. Removing that with the flush chems increases the amount of R-134a that will pass through the hose walls.

It was definitely worth the conversion, should anyone have doubts.

Should be concerned about the extra oil volume left in the system if I don’t do the chem flush? Also I was considering replacing the condenser with the modern parallel flow type.
Thanks for the help.

[AZMI951]

If you are converting from R12 o R134, flush the system and stat fresh. R12 uses mineral oil and R134 uses PAG oil. They are not the same and not compatible. Autozone rents a flush tool and the AC flush solvent is like $25 a gallon. Just do it right and get those 38 degree vent temps for years.

[Tom]

If you are converting from R12 o R134, flush the system and stat fresh. R12 uses mineral oil and R134 uses PAG oil. They are not the same and not compatible. Autozone rents a flush tool and the AC flush solvent is like $25 a gallon. Just do it right and get those 38 degree vent temps for years.

Griffith's recommends ester 100 since it's compatible with mineral and PAG. Worked for me. I'm sure flushing and starting over is probably better advice though!

[dr bob]

Should be concerned about the extra oil volume left in the system if I don’t do the chem flush? Also I was considering replacing the condenser with the modern parallel flow type.
Thanks for the help.

You'll have all the plumbing connections for the condenser already removed, so it's short work removing it for flushing. The thin R12 mineral oil film oil film on the condenser tube walls is negligible if you don't flush, but then presents you the need to use the polyolester oil as Tom mentions. Oil lives in the compressor, so part of your conversion will be a series of manual drain-and-fill exercises while it's out. You'll need to add back the full system charge load of the polyolester oil to the compressor before you reconnect to the system.

Very Important: Once you have everything reconnected and while you have the vacuum pump connected for a bit, rotate the compressor by hand a dozen rotations or two before you put the belt on. That way any oil that might have found its way into a compressor cylinder will get pushed out before you try and run the compressor at engine speed. Saves damage reed valves, and often saves compressor pistons and cylinders themselves.

The largest accumulators of oil in the system are the compressor and the drier, then IIRC the evaporator and condenser in that order. Obviously the more of the old oil you can get out the better.

[dr bob]

Should be concerned about the extra oil volume left in the system if I don’t do the chem flush? Also I was considering replacing the condenser with the modern parallel flow type.
Thanks for the help.

Following on the advice shared by others --

You'll have all the plumbing connections for the condenser already removed, so it's short work removing it for flushing. The thin R12 mineral oil film on the condenser tube walls is negligible if you don't flush. You'll still need to use the polyolester oil as Tom mentions. Oil lives in the compressor, so part of your conversion will be a series of manual drain-and-fill exercises with new oil while it's out. You'll need to add back the full system charge load of the polyolester oil to the compressor before you reconnect to the system.

Very Important: Once you have everything reconnected and while you have the vacuum pump connected for a bit, rotate the compressor by hand a dozen rotations or two before you put the belt on. That way any oil that might have found its way into a compressor cylinder will get pushed out before you try and run the compressor at engine speed. Saves damage reed valves, and often saves compressor pistons and cylinders themselves.

The largest accumulators of oil in the system are the compressor and the drier, then IIRC the evaporator and condenser in that order. Obviously the more of the old oil you can get out the better.

[AZMI951]

If you are converting from R12 o R134, flush the system and stat fresh. R12 uses mineral oil and R134 uses PAG oil. They are not the same and not compatible. Autozone rents a flush tool and the AC flush solvent is like $25 a gallon. Just do it right and get those 38 degree vent temps for years.

Griffith's recommends ester 100 since it's compatible with mineral and PAG. Worked for me. I'm sure flushing and starting over is probably better advice though!

I always struggle not following a lubricant requirement from the OE. Denso specifies PAG 46 and on a newly flushed system there is no reason to worry about mixed oil or refrigerant. Griffiths may run Sanden compressors so the oil spec may be different. With the rising cost of compressors, $500+++, a little more time and effort flushing makes sense to me. It is not like we are working in a flat rate shop on daily drivers so we can afford to take the time to do it really well.