Have never used the front defrost button on my 964 (and I doubt it'll ever be used in the future), but I sold the car and it's needed for passing local inspection. Car is supposed to be picked up next week, so I need to sort things out quickly.

Symptoms: Every function on the climate control panel works, but when I press the defrost button, it comes on for like a second then stops? Feels like the button isn't making full contact or something? What's the first thing to check to start tracing this out? Hopefully I don't need to replace that whole panel....

Thanks for any help!

 

Check your the fan in the engine compartment. If that is not operating, the CCU will try to start the defrost cycle but then stops.

 

Thanks....complete rookie here, how do I check the fan?

 

Tore has the most comprehensive info on his site. There’s also a way to jumper the rear fan relay to check to make sure it runs. If it runs then you probably have a bad temp sensor or resistor:

https://www.bergvillfx.com/porschehvac2

 

Update: Fan in engine compartment is working

 

then it’s either the resistor, temp sensor or an issue with the CCU. Should be pretty easy to chase down, hope it’s not the latter 🙄

 

It if turns out to be a CCU issue....how likely is repairing the problem? Vs just replacing the whole unit (which the dealer wants ~$3k for)....even used they are $$$

 

if the AC and other HVAC operates properly the ccu is prob fine. Those resistors fail often and there is an updated part. I’d swap out the resistor first and see if that fixes it:

https://www.pelicanparts.com/More_In...16-550-02-M100


repair would mean sending it off and that’ll take a long time unless you find someplace to buy a new refurb’d and send your core in.
shoot tore a PM he is the 964 HVAC master.

 

Out of curiosity, why does this matter for local inspection?

 

Thanks for the reference Rocket Bob.
The thing is that the CCU will shut down the two front blowers if hot air is needed to the cabin and the rear fan fails to operate. You will see the same if you set the temp **** to maximum and turn up the fan speed.
Check the rear fan fuse, low speed resistor, relay and blower motor.
A DIY test procedure of the rear fan is available on this page: https://www.bergvillfx.com/index.php...on-system-test
Cheers,
Tore

 

You can send your CCU in for a rebuild for around $300.00, or purchase a rebuilt for around $800.00.

 

Just Canada........

Need to have working defrost even in a car that hasn't seen winter in the last 30 years

 

Tore, thanks for the link - that is very helpful. Will start tracing things out. Hopefully not a big CCU issue - like I said, car needs to be on a truck Monday!

 

Update: Technician at Porsche cleared some faults in the control unit - now everything works. Weird. Thanks everyone for the help!