Need some help to help diagnose my A/C system on my 1988 928 S4. It is still on R12.
1. A/C Blows warm after depressing the A/C button with all fan settings
2. Two Cooling fans in engine bay are running
3. Compressor is turning, not sure I hear it cycling the clutch since it is noisy with engine running
4. A/C sight glass- don't see bubbles and do see liquid passing
5. A/C Manifold Gauge readings
- With engine off, low side shows 40 PSI, high side shows 50 PSI
- With engine on, low side shows 0 PSI, high side shows 50 PSI
Looks like the compressor is shot but the 0 PSI on the low side is throwing me off so I want to rule out everything first. Also I don't see the pressures changing so not sure the compressor clutch is cycling (should the clutch cycle showing pressure changes?)

Anything else I should check for? I did add 2 cans of R12 about 4 months ago and it did cool some but not great, but I have not used the A/C all winter and now it's blowing warm.
I was going to evacuate the whole system and pump a vacuum on it using another member's pump once available and then recharge to the correct weight of R12 to try again but are there any other symptoms pointing to something I should address before I try to vacuum and recharge. R12 is expensive so don't want to do this until I have to.

Thanks,
Mike

 

Sounds like a failed pump. If it was the expansion valve the high side pressures would be extremely high.

Your freon flowing through the sight glass means that it certainly isn't a leak. The internal seals in the compressor have probably failed and getting either a good used or rebuilt part is in your future.

Best of luck on fixing it.

 

Thanks

 

When I replaced my AC compressor, I ordered it through Greg Brown. It was surprisingly affordable at the time.

 

First, look for leaks you can fix before you recharge, normal places are compressor seals, 2 hoses at the compressor, expansion valve o-rings.

I've owned 3 sharks, 78,84,89, all cooled quite well with R134a up to 95F ambient with no problems.

After you inspected for common leaks, convert to R134a, if you need details drop me a note. Properly evacuate, recharge and test.

Your low static pressure suggests you are low on refrigerant, and if you did not properly evacuate the system when you added the 2 cans prior you will not get good results.

http://griffiths.com/product-categor...tioning/928-2/

 

Thanks Nicole.

 

Thanks. Will drop you a note.
Mike

 

Mike-

Your pressure readings suggest that you are way low on refrigerant. The 40-50PSI you see on the gauges says that there's a small aount of gas remaining in there. Since it pulls the suction side down nicely, I'll venture that the compressor is likely fine. There's no liquid at all flowing through the sight glass at the pressures you note, all ou are [not] seeing is the vapor flow.

But you do have leaks, otherwise the pressures wouldn't be so low. You'll want to identify and fix all of them of course. The original o-rings and such are tired and hardened at this point in their life, so the first order would be to replace all of those. You'll want a new expansion valve (2 if you have rear air) while the old one's out, and a new drier. Drain the old oil out of the compressor while you have it out for o-rings, and put the correct amount there, then the rest in through the charge port while vacuuming prior to recharge.

Griff has offerings for R-134a conversion, something I recommend. Did mine fifteen years ago and the cooling i still fine. You can currently buy R-134a easily in most places, while R12 is a little more spendy and generally way less convenient to find locally.

Buy or borrow a good book on auto AC systems before you just dive in and start replacing parts and pieces. Remember that surgical cleanliness is required working on for AC systems, so an early part of the project might be a little sanitizing under and around the engine and engine bay.

 

Thanks Dr. Bob