Date: Tue, 21 Sep 1999 15:51:44 +0000 Author: "Dr. Bob" Subject: re: AC Compressor not kicking on Body: Bryan wrote to the list: >> Hi all, >> I know this has been discussed repeatedly, but >> my search of the archives didn't come up with >> anything very specific. I have an '89 S4, that >> the air was working in until last week. Up to >> then, it would cut out and blow warmer air every >> once in while, but would always come back on within >> an hour max, which led me to think there might be a >> loose wire or low freon level. So I had the level >> checked this week and it was full. <> Hi Bryan: There's a diagnostic procedure you can follow to isolate the "comressor won't run" problem. Starting at the wire to the compressor, check for voltage while the AC button is pressed. If there is voltage at the compressor with the wire disconnected, connect it back up and immediately go to the temp switch under that plastic rain shield, base of the windshield. Check for voltage at either terminal to ground without disconnecting any wiring. If the voltage there is no very low or none, you have a bad relay in the dash controller. I'm sending you a detailed diagnosis and repair procedure for the controller. If you're not up to doing the relay mod, you can get new, used, or rebuilt dash controllers from Dave Roberts or Mark Anderson for sure. The circuit for the AC clutch runs back from the clutch through a wire connector that hangs on the main wire bundle in front of the air pump on my similar '89. The circuit traces back through pressure switch next to the drier. The switch is the lower devive with the two spade terminals in the single plug; the pressure transducer for the fan-and-flap controller is the one on top there with the two eye terminatls attached with little nuts and washers. Circiut continues back through the multipin connector that's part of the jump-start terminal on the right side of the engine bay, and back through the freeze switch under the plastic tray, middle of the car at the base of the windscreen under the hood. The freeze switch receives power through the relay in the dash controller. Of course, basic troubleshooting always starts at the fuse, so begin there. However, your symptoms of erratic operation and periodic warm spells in the car are identical to what I found in mine. The new controller relay cured it completely. On my list of things to do is order a box of the service relays. Once I have that minor task under my belt, I'll be able to offer a repair service. I'll post to the group when that's available. In the meanwhile look at the instruction I'm sending you to give yourself an idea what's involved. dr bob From: Wally Plumley [wplumley@bellsouth.net] Sent: Wednesday, September 05, 2001 10:37 PM To: 928 Subject: [928] Re: a/c compressor options At 08:50 PM 9/5/01, Mark Litherland wrote: >Ever have one of those days it just doesn't pay to get out of bed? After >the single most frustrating day at work I've had in months (nothing >worked, everything broke) all I wanted to do was head home, mow my grass, >and relax a little. I got a mile from my house when the compressor siezed >solid, killing the engine. yay. Of course I didn't have a knife so I >hoofed it home in my work clothes, got a knife, hoofed it back, cut the >belt and drove home with no more problems. > >Yes this is the one part that didn't get replaced in my recent a/c >work. yay again. So my question, are there any other options besides a >rebuilt stock unit? I put a Sanden rotary in my 911 years back, is there >anything like that for the 928? I'm looking for the budget option here, >my wallet is painfully low at the moment. Anyone ever rebuilt a >compressor themselves? I can source bearings pretty easily. If the compressor locks up, all you have to do is to turn it off. If that wasn't the case, then what locked up wasn't the compressor, but the compressor clutch bearing, which can be replaced on the car without losing the refrigerant. Wally Plumley 928 Specialists -----Original Message----- From: griffs@griffiths.com [mailto:griffs@griffiths.com] Sent: Tuesday, March 12, 2002 7:31 AM To: 928 Subject: [928] AC Compressors (lockup, freezing, noise) Thought these comments might help resolve questions regarding compressor problems noted on the list: There are numerous reasons for compressors bumpin belts, locking up or making internal noise. If the belt has jumped the track it is more often the result of the compressor locking up (either for good or for the moment, and in either case you might as well write off the old compressor). Lock-ups are a result of either (1) poor lubrication or (2) high system pressures. (1) Lack of lubrication can be caused by a few scenarios: (a) Low refrigerant levels - caused by system leaks or restrictions. The compressor needs a constant flow of oil. The oil is carried by the refrigerant, so if you have low refrigerant flow you have a low oil flow. If the system is constantly running with a "border-line" low pressure, the compressor life will not be long. Repair all system leaks, such as hoses, expansion valves, fittings, condenser, evaporator or the compressor itself. (b) Oil traps - on systems with dual evaporators there is solenoid valve at the rear evaporator system. We have seen solenoid valves that are not completely closed when the rear system is turned off. If the solenoid valve is partially open by a hair, refrigerant will pass through the small opening and oil will collect in the rear section of the system. In time this collection of oil will reduce the total system oil level to the point that the compressor will "lock up". (c) Failure to replenish the oil supply over the years when "topping off" a system - typically this happens when an owner notices bubbles in the site glass and attempts to add more refrigerant to the system without adding more oil. If you are wondering how much oil you need in the system and you need to guess, here is a good rule of thumb that works (on the 1980+ systems), when replacing the compressor have at least 6 ounces of oil in the compressor, if you replacing another major component (condenser, evaporators,drier) add 1 additional ounce per major component. R12 refrigerants use "refrigerant mineral oil" and R134a refrigerants use either ester or pag type refrigerant oil. Ester can be used for either R12 or R134a refrigerants and we have found it has an excellent performance record. Keep in mind that if you have too much oil in a system you will have poor performance as the extra oil will coat the condenser and evaporator walls which reduces the transfer of heat. (2) High system pressures or high "head" pressures can be caused by a few problems: (a) overcharing the system, usually happens when we try to accomplish the charging task by purchasing those economical cans of "drop in" refrigerants from the local parts store and we fail to use pressure gauges to monitor the system. (b) condenser fan failure, dirty condenser fins, internally contaminated condensers, (c) expansion valve failure, or (d) not common but it happens - mixing refrigerants. About Clutches: (a) Most clutch bearing failures, other than simple high mileage, are caused by heat. So if you have either low oil flow or high head pressures the heat moves quickly from the aluminum compressor to the bearing on the nose of the compressor. The grease in the bearing melts down and the bearings wear out. (b)Clutch coils typically fail because of heat rather than indirect electrical shorts. As the heat builds up in the aluminum compressor it is transferred to the steel can and copper windings making up the clutch coil. The windings are covered with a thin layer of insulation and are packed in the steel can with epoxy. The insulation breaks down quickly with the high heat levels and sooner than expected the coil windings short out. You can imagine as well the transfer of this excessive heat to the bearing and visa da versa. Stay Kuehl! http://www.griffiths.com