ACEparts_com

Can anyone help? My A/C compressor runs continuously regardless of the settings on the controls. The only thing that stops it is to remove the AC relay in the engine compartment. I've tried replacing this.

Anyone know the solution?

ACEparts_com

Update. I've just unplugged the CCU (heater control unit?) and started it up, two seconds later the compressor starts running again on its own!

Stealth 993

I would check for a short.

Barney1

Sounds like the max cool button (the top snow flake) is stuck in the on position. Push on the button hard and see if it is in the out position.

ACEparts_com

Anyone else have any ideas? When the grey relay is removed from the engine bay the compressor stops. The odd thing is that it's getting a controlled signal from somewhere as it only engages a few seconds after the engine has started.
Anyone have a wiring diagram to hand ? :O)

TIA

ACEparts_com

Update, still having this issue. Just a couple of seconds after the engine starts the AC compressor clicks in. Only removing the relay will stop it. It's a short somewhere but a wiring diagram would go a long way towards helping if anyone has one? :O)

Thanks

ToreB

I think the 964 and 993 have the same wiring with respect to your problem ACEparts, Here's a link to some schematics:
http://www.cannell.co.uk/Manuals.htm

As far as I can see the A/C compressor relay get it's power from the CCU through the 3-level pressure switch. You have checked the relay, but also if it get a +12V signal to pin 2, relay coil?
If so, there also may be +12V to the 3-level pressure switch with the CCU disconnected?
If that is the case there must be a short or something, if the CCU is disconnected there should be no +12V in that circuit.
You find the 3-level pressure switch in the luggage compartment under the windscreen, see picture here:
http://www.porsche964.co.uk/technical/climate.htm
You can see the pressure switch mounted on the metal pipe on the right in the picture with the blue wires.
Regards,
Tore
Oslo, Norway

helmet155

Bad relay?

BS911

I used to have a copy of the whole system schematic on this but have lost it. As I recall though, as said above, if the CCU is unplugged then there should be no power going to the 3 level switch and therefore no power to the relay in the engine compartment.

+1 on the relay.

helmet155

Measure the voltages at the relay on the harness side while actuating a/c switch. I didn't want to say relay since it's simple and assumed you checked it But...check it, probe the female pins of the connector and see if you have power going to it when actuating the switch.

Maybe easiest to just check continuity inside the relay, if you have continuity it's stuck 'closed' and gives you power at all times.

ACEparts_com

Well, i'm stuck. The orange/white wire goes to ground soon after the engine starts. Where does this wire go to (N143)! HELP!

ACEparts_com

Another thing - one of the front blower fans is dead, no way am i paying £500 for a new one - what's the alternative? VW part perhaps?
Cheers

Deadeye

check with viper bob, he's parting out a 993

helmet155

3 level pressure switch...and also feeds the catalyzer warning lamp in the clock. pages 1168 and 1154-1155 of the PDF manual noted above.

Uber 911

The oil cooler or AC, if the latter its not going to help the problem.