It's July in Texas and the air quit working recently. It worked fine going to work and when I got in the car to leave, no air. There are no apparent noises and compressor appears to be turning normally. Compressor simply doesn't engage when switched on. I've checked wiring and all appear to be connected and showing juice. Any tips on testing compressor, etc. would be helpful. It is on a '87 740 GLE non-turbo wagon. Thanks! TPW

Put gauges on it and see if there is any freon pressure - not likely. Freon could have leaked from a variety of places - hose, fitting, compressor seal, evaporator, condenser. Maybe you got a rock in the condenser - it happened to me on my Dodge Minivan.

If there is no freon pressure, you can apply positive air pressure to the system and listen/look/soap bubble test for leaks. They're usually easy to find.

Good news is that if you had a freon loss because of something other than a compressor seal failure, your comp should still be good. Make sure you check the oil level in the compressor, because you can lose oil if the system blows down through a leak.

I will check with gauges to see if the system has freon. However, I feel like there is likely freon in the system since it happened so quickly. I really appreciate the help! Thanks! TPW

Hi Thom, Jim the advice is good except for use of compressed air to pressurize system. Compressed air is full of water unless you're in a very dry part of Texas, water and refrigerant and aluminum parts are a bad mix. Water + refrigerant makes hydrochloric acid which is very unfriendly to the aluminum evaporator and condensor. Better to pressurize the system with a can of refrigerant or use compressed nitrogen. (I realize not everyone has compressed nitrogen in their basement) A quick way to see if there's pressure is to remove the clutch cycling switch from the accumulator. If there's pressure a little bit will escape as you're unscrewing the pressure switch. As further confirmation you can depress the Schrader valve on the accumulator port once the switch is off, taking precaution against getting it in your face. On a warm day with the engine off the pressure in the system should be about 80 psi. If you've got that then the problem is likely electrical, such as the clutch cycling switch , the compressor field coil or the HVAC control panel on the dash

I checked the system and it is pressurized (65+ lbs not running). I really think it is an electrical related problem, i.e, clutch cycling switch or the compressor field coil as you suggested. Can you or anyone else tell me where those are located and if there is a way to test them? Thanks! TPW

Hi Thom, I don't have a schematic beside me but the clutch cycling switch is on the accumulator; there should be 12V + on one side when it's unplugged and voltage on both sides when it's plugged in. The compressor clutch field coil is down there on the compressor, natch, you should check both sides of the plug for 12V+ and a good ground on the other wire. If you've got juice to the clutch but it's still not engaging I would give it a little tap with a long screwdriver (the outside front part that's not turning) but be prepared for it to start turning when you give it the tap! If that happens then it means that the clutch has worn out enough so that the air gap is too much for the field coil to pull in the outer part (the shoe). The quick fix is to pull off the shoe and remove one of the shims that create the air gap. If you don't have 12V+ at the clutch cycling switch then the problem is likely in the HVAC controls, a fuse or a relay. Since I don't have the electrical drawing at hand I can't help you there today. I recommend that you use a 12V test light for the electrical tests, not a multi meter. Meters will show a voltage but it may be a 'ghost', a test light will not light unless there's the current to back it up.Always test both sides of a circuit, 12V+ is great but useless if the ground wire on the other side of the circuit is broken. To test for 12V+ attach the alligator clip of the test light to the engine block or the negative battery terminal and probe the switch for the + voltage. To check grounds attach the alligator clip to the positive battery terminal.

Tom:



Nitrogen is not available to the home mechanic who wants to get his AC system fixed on a Saturday afternoon with the minimum amount of trouble.

I only have compressed air on the system for less than five minutes because that's usually all it takes to find a leak. My compressor has a water separator on it. The air is static in the system, not flowing. With the little quantity of air that it takes to fill an AC system at 40 psi and the little time involved, there is no way that the dessicant in the filter-dryer will become saturated or that any residual moisture will be left in the system after evacuating it for 30 minutes to an hour. Considering that an open system in Houston will naturally pick up some humidity while you're working on it anyway, I doubt that introduction of air onto the system for a few minutes to check leaks is a problem.

Hi Thom, Jim the advice is good except for use of compressed air to pressurize system. Compressed air is full of water unless you're in a very dry part of Texas, water and refrigerant and aluminum parts are a bad mix. Water + refrigerant makes hydrochloric acid which is very unfriendly to the aluminum evaporator and condensor. Better to pressurize the system with a can of refrigerant or use compressed nitrogen. (I realize not everyone has compressed nitrogen in their basement) A quick way to see if there's pressure is to remove the clutch cycling switch from the accumulator. If there's pressure a little bit will escape as you're unscrewing the pressure switch. As further confirmation you can depress the Schrader valve on the accumulator port once the switch is off, taking precaution against getting it in your face. On a warm day with the engine off the pressure in the system should be about 80 psi. If you've got that then the problem is likely electrical, such as the clutch cycling switch , the compressor field coil or the HVAC control panel on the dash