From: Dr. Bob [dr.bobf@worldnet.att.net] Sent: Sunday, August 13, 2000 3:22 PM To: 928 Subject: [928] re: aircon. connections Juan posted the following to the list: > > > >Can anyone tell me where can I find the electrical connections to the >aircon. compressor? It fails to kick in when I switch the aircon. on. >Lets hope a bad electrical connection is the problem. If anyone thinks >there may be another problem I'll apreciate the advise. It has run fine >so far (until this weekend). > >Thanks > >Juan >'93 GTS 5spd Juan: The connections, working back from the compressor to the controller: There's a plug connector in a single wire where the compressor clutch coil attaches to the wiring harness. The wire routes from the top of the compressor unit, forward in the car to come out next to the air pump (on US cars). The connector on mine is tie-wrapped to the main wire harness bundle that runs across the front of the engine, above the crank pulley near the spark plug wire bracket. The wire runs through that main harness, and connects to the pressure switch on the AC receiver/drier unit. The drier is the cannister that sits at the right (passenger side on LHD cars) side of the car, in front of the radiator and air conditioner. S4/GT/GTS cars have a separate pressure transducer for fan and flap controls, with screw connections. The pressure switch on mine has flat spade terminals in a two-wire molded connector. The pressure switch is the lower of the two devices on mine. The wiring from the switch continues back through that same harness, and is included in connections in a multi-pin connector that is mounted on the right (passeneger side on LHD cars) side of the top of the radiator sheet. It's a flat plastic shell that splits horizontally. From that connector, the wiring continues back to the freeze switch that's mounted at the base of the windscreen. With the hood open, carefully remove the plastic rain shield tray behind the air filter box. The freeze switch is a metal box about 1.5" cube, with two electrical connections and a capilary tube about 3/16" diameter running toward the left (driver's side on LHD cars) side of the cowl, then into the evaporator box. The switch itself is mounted almost centered under the front of the windscreen on a metal angle bracket. Current for the circuit is supplied through a relay in the dash controller. Check your fuses also. Common causes of your problem include low freon pressure in the system. The pressure switch detects the low pressure, and opens to protect the compressor from running without gas and oil circulating in the system. A set of refrigeration gauges and hoses will confirm the situation. Owners have reported problems following timomh belt servioce, when the connection at the compressor is left loose or not connected at all. The relay in the dash controller failed on my car, and similar failures have been reported by others. I have documented the repair procedure, and a copy is available on request. Hope this helps! dr bob From: V1UhOh@aol.com Sent: Sunday, August 13, 2000 1:57 AM To: 928 Subject: [928] Re: aircon. connections hey Juan check under the plastic rain pan under the hood, near the windeshield. On my 87 there is a temp switch of sorts that if the evapotator gets tooooooo cold it shuts of the AC. If there is a fault here the AC may not run. When i bought my car the PO had spliced the 2 wires that go into the sensor together to rid himself of this problem (this would be a RUN ALWAYS SOLUTION). on my 87 the wires are purple/ yellow in color and enter the blower tunnel in front of the evaporator area. Tony From: Wally Plumley [wplumley@bellsouth.net] Sent: Friday, December 08, 2000 10:35 AM To: 928 Subject: [928] Re: 928 digest: December 07, 2000 At 09:33 AM 12/8/00, Gary wrote: >Hi, > Does anyone know what the two sensors on the side of the >receiver/dryer on an '87 S4 are for? >One has two quite large connectors from the top, and the other has two small >connectors on the bottom. >I assume one is a low pressure switch - what is the other & which one is >which? The one that looks like an oil pressure switch, mounted on the side or the receiver/dryer, is the low pressure switch. This one cuts off the compressor if the freon pressure gets too low due to a leak. The one mounted on the stem on the earlier cars is a freon temp switch, to turn on the aux electric fan when the freon gets hot. On the S4 and later cars, the freon temp switch is replaced by a freon pressure switch to tell the computer when the A/C compressor is working, so the computer can control the two electric cooling fans. Wally Plumley 928 Specialists -----Original Message----- From: Wally Plumley [mailto:wplumley@bellsouth.net] Sent: Saturday, September 21, 2002 7:48 PM To: 928 Subject: [928] Re: AC compressor relay At 03:51 PM 9/21/02, Mark Litherland wrote: >Well after a week with AC it stopped working again. Grrrr. Nothing wrong >with the hardware, it's all new. Vacuum switches are "ssshhhh-ing" >properly and the blower is working fine, but the compressor never comes >on. Looks like an electrical problem. Using Dr Bob's diagnostic >procedure, I checked voltage at the pressure switch and found 13V. Then I >checked both sides of the freeze switch and found very low voltage, ~0.5V. > >Ok need some assistance, I'm an electrical novice and the wiring diagrams >are complete Greek to me. My new compressor from Griffiths has only one >wire going to it that I can find, a very thin wire connected to the >top. When Bob says to disconnect the compressor to test the freeze >switch, is he talking about that wire or something else? I disconnected a >large connector next to the freeze switch and the low voltage became ZERO >voltage. > >I think I may have a relay problem in the control head, but have no idea >what it looks like. I can't figure out which pin/connector to trace >back. Anyone have the pin numbers? > >Or am I barking up the wrong tree and need to look elsewhere? Anyone got >a simple "connect MM here, check connector there, test pin #x" kind of >diagnostic? It kills me, the amount of money I have in the AC on this >car, and now it isn't working AGAIN. You probably have one simple problem that you haven't fixed yet. Checking voltage doesn't always tell the tale on the A/C clutch circuit. It is very possible for the little blue relay to pass enough voltage and amperage to light a small test light, or to show 12 vdc on a meter, but not to pass enough amperage to operate the clutch. Go to the low pressure switch on the A/C receiver/dryer. With the plug still attached to the switch so that it will operate the compressor clutch, hook a voltmeter between one of the terminals and a good ground. Turn the ignition switch on, and turn the A/C on. If you get 12 vdc and the clutch clacks, your problem is elsewhere. If the voltage is less than 11 vdc, and the clutch doesn't clack, either the blue relay or the anti-freeze switch is probably bad. If so, remove the plastic cover at the base of the windshield and find the anti-freeze switch. Square block, about 2" x 2", with two electrical connections and one small capillary tube, mounted near the center of the car near the A/C tubes. With the clutch hooked up (no disconnected wires) check for 12 vdc between each of the electrical terminals and a good metal ground. You should get 12 vdc on both. If you get it on neither, the little blue relay may be bad, or the problem may be between the relay and the central power panel. If you get 12 vdc on one connector and not the other, the anti-freeze switch is bad. A simple series string - just find where you are losing the voltage. Wally Plumley 928 Specialists