Need help before I go back to mech this aft.

Pls bear with the details.

I usually get my A/C serviced annually. Was late this year. Heres the deal.

0800 Wednesday
A/C working just fine then went warm near the parking lot at work. I flipped the hood and the compressor clutch had disengaged. Clutch would spin freely. Called mechanic. He said swing by in the afternoon and he would check system. I remember him telling me years ago that my compressor has a fail safe that disengages the clutch if freon level falls too low. I really didn't think it was any more than that. Takes about a pound every 2 years. Read FAQs to try to diagnose problem.

1430 Wednesday
I opened the hood prior to starting the car. Started car, turned on A/C, ran to front of car. Clutch engaged for about 2 seconds, then released. Windows down. Went by house (8 miles driving) to get pot luck supper stuff to drop at wife's office. Concerned about outside temp, perishable food and sleeping on couch. Cranked up A/C and rosary beads and A/C worked. Drove to wife's office (again another 8 miles). A/C worked for about 7 of the 8 miles. Pulled #16 Hot as hell!!!! Actually almost too hot to hold.

Dropped off food. Drove to mech (another 10 miles). Ran A/C whole way on recirc. No problem. Mech evacuated system and put in 0.7 lbs of freon. ($107 for all) Back to office (20 miles). A/C on the whole way. No problem.

1900 Thursday
Heading home. Sunroof open, tunes playing, A/C on, life is good. Half way home, compressor clutch released. #16 warm, but not hot. Problem!!!

0800 Friday
Off to work. Repeated hood pop scenario. Clutch engaged, then disengaged almost immediately.

Back to Mechanic this aft.

Any takers.

BTW, it is veeeerrrrry scary when your mech is working on your brick in the shop and you are in the waiting room reading his latest boating magazine whose feature article is "The World's 100 Largest Yachts" and you remember about 6 months ago him mentioning trading up!!!!!!!!!!!
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Regards,

David
1991 744 NA 139+K Miles

UPDATE!!!!Mech assures me the problem is electrical. No power to low pressure switch. He bypassed the relay and ran power directly to the pressure switch and the compressor ran fine.

Replaced motor and trandmission mounts this W/E. Car sat in driveway for a cuople of days.

Monday 0730
Muggy but outside temp was not too bad, high sixties. Started off for work with windows open. About 5 minutes into trip, switched on A/C to see if it would work. It did for about 5 minutes, then could feel the compressor disengage, and warmer air from vents. Leads me to believe it is a bad relay / board.

Question to all. Is the most likely failure point the relay, or the board? How difficult is the soldering of either?

Bizarre question to all. Can this relay be bypassed with a toggle switch and direct wiring, or does the relay have something to do with the cycling of the compressor?
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Regards,

David
1991 744 NA 139+K Miles

When the a/c quits working check to see if there is power at the compressor clutch. If there is the clutch is bad and needs to be replaced. If there is no power to the clutch, check for power at both terminals of the pressure switch mounted on the accumulator(silver can passenger side firewall). If the freon quantity is to spec's the pressure switch will allow current to flow through it and on to the compressor clutch. If there is power on one side of the switch but not the other, remove the connector from the switch and jump the 2 terminals with a piece of heavy wire. The compressor should then run. If it does and your freon level is correct, then the pressure switch is bad. There is a scraeder valve located under the switch so you can unscrew it and replace it without loosing much freon. Do not run the compressor long without the switch working. If the freon level is low, there will be little refrigerant oil circulating through the system and you could burn out the compressor. If there is no power at all at the pressure switch then there is a problem with a fuse, inside wiring, the manual climate control ECU, or a combination of the above. I have read that the ECU in these cars is known for poor solder joints on the circuit board. This may be your problem, but check out the above suggestions first and let us know what you find.

If you don't need more charge, then it is most likely your compressor clutch slowly failing.

.7 lb should not be enough to disengage the clutch via the pressure switch, unless it is out of adjustment, which is a possibility I suppose. if that is the case, every tie you lose the slightest amount of freon you will be taking it to the repair shop, so if you only need a shot of freon to get it to work correctly again, then you need your mechanic to adjust the pressure switch for you.

Hope this helps