'99 S80 Finicky A/C

[sfvstyle]

Hey guys,

I have a 1999 S80 2.9 with around 124,000 mi on her. She's been a good girl for most of the time I've had her (since '04) and I love the space, creature comforts, and sophistication provided in this car over those of the same model year.

However--and there's always a however-- my A/C has been a bit botched for years. When the summer months roll around in the San Fernando Valley, temperatures like to hover around 108; and my a/c compressor tends to give up momentarily. I was told by my Volvo dealer that the A/C clutch was packing in, and judging by the rapid cycles, I believed them. I figured I'd wait it out and see what happened, and up until 2010, it would only be a problem for brief periods.

This last summer was hellacious. Toward the end, I was getting cold air at the beginning of my journeys, but by the end I'd be using the "565" air conditioner: 5 windows/sunroof open, 65 mph on the highway. Blisteringly hot in the sun and 108+ degree ambient temperature.

I know that when you apply full throttle, or hit the kick down point, the A/C compressor switches off to prevent A/C damage and provide best performance. On the fwy in LA, I'd need to do this quite often to pass people (especially in a 2.9). Air would be cold until I did this, but the a/c would not re-engage afterward, and I'd press the A/C button on my climate control, leave it off for a minute or so, then turn it on again and it would work-- only for a time, regardless of full throttle/kick down.

I took notice of whether I could hear the clutch engaging or disengaging, and I would hear it sometimes make a sound like that of a slip up-- it would kick on, kick off immediately after, then remain off for a while, maybe kick on again, then throw in the towel. In essence, it seems that it would try to go on and sometimes fail, try again, succeed, then give up and stay off. Notwithstanding, at night the A/C works admirably.

My question to you is this: Is this a clutch failure, a computer (auto disengage upon full throttle) failure, or a compressor as a whole failure? Obviously I'm leaning to clutch and or computer. Also, what would it cost to have these components repaired, rebuilt, or replaced? Is there any way I can do a little simple DIY work on the clutch myself?

Many thanks to you, and I hope that 2011 is off to a great start for everyone here at MVS.

Adam

[jimmy57]

The clutch air gap between drive pulley the front driven plate can cause engagement problems that show up after the compressor body gets hot from engine running. The magnetic coil gets hot and its resistance goes up which lowers it magnetic force. When the force falls below a certain level then it no longer has the strength to pull the plate in to drive pulley. The task of removing a shim to decrease the clearance from wear is easy once the hard task of gaining working room is overcome.
Usually when this occurs the milage is high and a shop will replace compressor as they get warranty backing for part and a new compressor is a no-brainer fix.
BUT: other things can give the same symptoms. Some 99's have a temp switch on back end of compressor down below the where the A/C lines attach. The switch can cut out compressor for high temp. Usually the reason this occurs is the refrigerant level is a little low and the small amount of still evaporating refrigerant that can keep compressor cooler is not there and after the same lengthy drive where engine heat conducted into compressor body, the temp switch opens the circuit and it takes a while for it to cool enough to allow current to clutch again.
Look at compressor, if the temp switch (brass with two wires that can be followed to clutch wiring) is there on compressor then have 1/2 pound refrigerant added and see if the problem is resolved.

Another item that can give the same symptoms is a faulty evaporator temp probe. If your car's chassis number is 030000 or less that will be on right side just to left, behind and above where the air filter inserts into HVAC case. Past that approximate chassis number the sensor is above and to the right of accelerator pedal. THe way to check this is to drive car until the problem surfaces and then have someone read ECC parameters with a scan tool capable of displaying ECC info. The evaporator temp not being in agreement with the real temp of discharged vent air temp is the clue to his being the problem.

The diagnosis by dealer of clutch may be accurate and point to clutch gap adjustment or replacement of compressor.

Rapid cycling of compressor on the a/c system on 99 s80 and other P2's is not unusual and may not mean anything. Low refrigerant on many of the other volvos is an indicator of low charge but that car uses a TXV refrigerant control system with that evap temp probe and when the cooling demand is low the evap temp probe signal will change rapidly enough that ECC will cycle compressor off within seconds of clutch engagement and off again when the temp falls from refrigerant flowing.

[sfvstyle]

Thanks so much for your quick and detailed reply. I'm in contact with a Volvo mechanic back at home in LA (I'm in South Africa right now) and he thought it could be low refrigerant-- probably thinking along the lines of that temperature switch, if equipped. I'll see if I can get my parents to take it over there, although I think I'll probably have to wait until I get home to check out what you mentioned and collaborate with the guy to get it sorted.

Thanks again!