Greg H.

I read all the archived A/C threads and it seems most people have the opposite problem. My clutch is always engaged no matter what buttons are pushed, key on or off. The a/c appears to be going all the time, but the climate control seems to work properly. I had the heat on today and everything was great.

I hope it's the A/C relay, but was wondering if it might be a CCU failure or something else. Anyone seen this problem?

Greg H.

Garth S

Disconnect the single wire from the AC compressor - a female spade connector on ~10" of wire: if the clutch does not disengage, the clutch is dead .... if it does, then there is +12V at the male spade ( which you can verify with a meter) ... which indicates a CCU issue: I believe the AC relay is integral to the CCU, as in the 928's, as I do no recall a separate relay in the CE panel.

Aha, the AC relay is in the engine bay panel, left side and in slot #3 .... easy to swap out with another similar relay for a test.

ToreB

Never seen that one before, you may have a faulty relay yes. Or maybe a stuck magnet clutch?

Pull the relay and test if there's any +12V on terminal 2 (pin 85 on the relay) That's the control input from the CCU. This signal goes through the 3-level pressure switch in the luggage compartment to disengage if there's any problem with pressure.
If the clutch disengage when pulling the relay you at least have a good clutch.

Do you get any warm air at all? If not you may have a problem with the CCU itself. But, don't despair, almost all of the internals in that can be fixed.
You could also pull out the CCU and test if there's any +12V on the K24 terminal/pin, both harnesses still connected to the car of course. If so, you may have a problem with the circuitry inside.
Regards,
Tore

Greg H.

Thanks for the tips, guys. I guess I should have been clearer: My clutch is engaged when the battery is hooked up, but disengages when the battery is disconnected. I do get heat and cold on demand. I assume the cooling system is running all the time because I just realized I get a huge puddle of water (condensate?) under the car after driving it - even when not using the a/c. I will check the relay first.

Greg H.

Humf

I have the same problem, ac clutch is constantly engaged, pulling the relay turns it off, but otherwise it is clicked on. The switch on the CCU has no effect. Any help appreciated.

ALLPRO

same problem of 964

green relay (in engine box) ac compressor is always excited
+12 constant

is "CCU" the problem?

very thanks

Opo

More likely low on freon imo

csmab

Low on freon. Mine did the same thing. Had it charged and it fixed the problem. Compressor would cycle on and off as expected after full charge. Even though the system was very low on freon it was still blowing cold.

nine9six

Rudy, Rudy, Rudy! ; )

Opo

😂😂👍🏼🙏🏼

ToreB

Low cooling media level does not cause the A/C clutch to engage, but the opposite. The three-level pressure switch will turn off the A/C clutch signal if the pressure is too low.

I guess this is a failed clutch relay. The fault finding procedure is mentioned above in Post #3.
I would recommend to remove the clutch fuse until this issue is resolved, the compressor can be damaged if it runs with low cooling media level. This also puts a uneccessary strain on the belt on engine startup.
Cheers,
Tore

ALLPRO

Hello Toreb, I'm your Italian friend

I'm just working on this issue and almost solved ...
As we talked about in days past, of the various contacts of the pressure switch between 964 and 993

In my case was mounted a non-original pressure switch, then unsuccessful, cut the wires to add, another anti-bridging control, and mixed the wires ...

I removed the additional probe, and reset the order of the wires ... now the compressor only pauses with the button pressed ... so it works perfectly.

There is only one problem, almost immediately the fast fan, (ok new and working resistance), most likely, the competition switch is a bit damaged or too much pressure on the plant to be tested.

Soon new updates ....

ToreB

Great news, thanks for the update.
Cheers,

pp000830

Doesn't the compressor run even with the heat on when defrosting?

ToreB

The A/C compressor engages when pressing the A/C buttons or Defrost. The evaporator will dehumidify fresh or recycled air.

Cheers,
Tore