How would you fix this A/C?
 

I just bought an '87 911 and the A/C doesn't blow cold. Tonight I hooked up some gauges, started the car and turned the air on. My gauges didn't move at all. Compressor clutch was pulled in. Strange. I shut off the car and disconnected the gauges. I pressed the shrader valves in with a screw driver and nothing came out on either side. No freon! (but the compressor did cut on before??) So I decided to pull a vacuum to see if it would hold. I pulled a vacuum for about an hour and didn't lose any so I don't think I have any leaks.

Now the question. What would you do to fix the A/C? Compressor cuts on and there appears to be no freon. Do I need any oil?? Do I need to change the receiver/drier and expansion valve? Or do I simply add freon?

Your thoughts are appreciated.

Thanks,

Scott

If you have zero pressure and "no leaks" you may have a slow leak. If you have stock hoses, they are designed to leak a little over time. Keep in mind that running a compressor with no coolant or oil will burn out the compressor. Are you sure the compressor is working?
You can start by adding coolant and oil. Do you know if the system has been converted to 134A? Does it have the original hoses or barrier hoses? For the money, I would seriously consider replacing the receiver/dryer (you may want to look into getting a Procooler instead).

I think a logical place to start would be to make sure the compressor is not seized and is receiving power to the clutch.

With the motor off, you should be able to turn the center section of the compressor by hand. With the ignition on and the motor off, you should be able to turn the ac switch on, and hear the clutch "click" on. Then you should not be able to turn the compressor by hand.

If that checks out, and you have added the correct oil, then recharge the system. The gauges will tell you if the system has a blockage somewhere. I think a new receiver dryer would make sense if the system had a big leak, but in that case so would flushing the system and blowing out the lines and condensors.

The York compressor does not have a low pressure cut out switch, so it will run even w/ an empty system. It's pretty resilient, but don't run it a lot with an empty system.

correct me if I'm wrong but didn't the '87 come with an ND compressor, or a Sanden maybe?

An A/C high/low pressure switch wasn't stock in a '87 so if you have a stock system the compressor clutch will engage even with zero refrigerant pressure.

The R-12 likely leaked out so I expect you have a leak somewhere even though it seems to hold vacuum. Does it hold vacuum when left "valved off" (no pump running) overnight?

Do you see any sign of oil leakage: streak on underside of engine decklid or around fitting connections?

If I were reviving the system I would first check the compressor for leaks. Then leak check the balance of the system. I would then dismount the compressor, drain and replace the oil.

The receiver/drier should be replaced.

The compressor appears to be working. When I cut the A/C on, the clutch pulls in and there aren't any weird noises like bad bearings in the compressor. I pulled a vacuum only for an hour and it didn't leak. I suppose I will pull another vacuum overnight and see what happens.

Assuming it holds vaccum, I'm thinking now about removing the compressor and draining/refilling with new oil. Since the system has now been exposed to the atmosphere, I will also replace the receiver/drier. I will then pull another vacuum and recharge.

How much oil should I add? I'm thinking 2 ounces in the compressor and 5 in the receiver/drier. However, since I'm not flushing the system, is there a risk of adding too much oil? How much R-12 does it hold?

Thanks,

Scott

I just went through a similar problem... After installing a Griffiths set of barrier hoses, new receiver dryer and a new compressor, it wouldn't blow cold air. First problem was a crack in the inlet hose of the rear condenser. Fortunately, it was made of copper and was repairable. Tried to charge the system again and still no cold air.

I traced the problem to a faulty expansion valve. It's the valve with coiled copper temp probes, that is attached to the entrance of the evaporator, in my case in the smugglers box.

$40.00 later, It now works fine...

ps. I have a factory Behr AC system in my 73 and luckly the expansion valve was a common item and was available from my local AC repair shop without having to special order it.

The expansion valve was clogged with dessicant from the previous receiver dryer so make sure you blow out the lines before you charge the system.

Scott: You're not focusing on a key point -- if your hoses are original, they're non-barrier hoses that are designed to leak. Back in the day, R12 was cheap and you could buy it at your local Pep Boys. Today, it's expensive and more difficult to get. If you're serious about getting your a/c to work properly, and not leak precious R12 into the atmosphere (Al Gore, are you listening?), you should replace your hoses and install barrier hoses. Both Griffiths and Rennaire make barrier hose kits. At the same time, you should replace your receiver/dryer as well.

These issues have been discussed dozens of times on this board. Do a search and you'll find a ton of information. And, if you see comments by Jim Sims, treat them as gospel. He and Charlie ("Kuehl") Griffiths are the a/c gurus on this board!

yeah, Kuehl and Jim Sims are the go-to guys on AC for sure.

My expansion valve was clogged too, which is why I mentioned the gauges as a way to diagnose a blockage. You have to read the high and low sides while the system is operating. It took about 3 total replacement expansion valves, after flushing the system twice and replacing 3 receiver dryiers and installing a brand new compressor before I got all the gunk out of my ac system. It was dead for who knows how long when I bought it.

I was wondering about the barrier hose kits myself. Why do they make the O.D. on these hoses so much smaller than oem? Can't I have my local ac shop make hoses by re-using stock fittings? Actually I have already done this on 2 hoses. Thinking about doing it on the rest as well.

OLD DISHONEST PORSCHE MECHANIC TRICK. TAKE A SCHRADER
VALVE TOOL AND TIGHTEN THE SCHRADER VALVES BACK INTO THE PORTS AND REFILL. ALOT OF BAD MECHANICS WOULD UNSCREW THEM A COUPLE OF TURNS AND ACCELERATE THE LOSE OF FREON OVER THE PERIOD OF USE AND THEN CHARGE BIG FOR A RECHARGE. MIGHT TRY TO FIND ONE OF THE OLD CANS OF FREON W/ OIL IN IT AND APROXIMATLY FOUR CANS (12OZ) OF R-12.
EMAIL ME IF YOU NEED SOME.

KEITH EPPERLY
87 SLANT NOSE TURBO LOOK CARRERA CABRIOLET

RUSNAK Wrote: I just got done installing a new barrier hose kit from Griffiths. The inside diameter of the hoses appears to be the same as the original cloth braded hoses. In fact, the outside diameter is a bit larger on the -12 hoses forcing me to spread the clips that held the original hoses.

According to Charles Griffiths, the new hose has a material inside that helps prevent Freon loss