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 appreciate the advise. It has run fine so far (until this weekend).


'93 GTS 5spd

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 canister 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 (passenger 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 capillary 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 timing belt service, 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


Hi All, I just wanted to remind folks that may be experiencing air conditioner failures, that the relay on the controller board has a history of failing. Mine went out last fall and I assumed loss of refrigerant was to blame so I put off fixing it until the weather started warming up. Following tips from Dr. Bob, Wally Plumley, Steve L. and others on the list, I decided to check voltages back to the controller board. Sure enough, I found my relay had failed and wired in an $11 replacement. My air conditioner has now been restored to its previous performance with much less effort than anticipated. This is a good first check.

Best regards,