StopLookGo

I've had a slight issue since owning my 964 for the past 2 years. It used to be very rare but it's getting a bit regular now. The Climate Control fans won't turn on at any fan speed. It used to be when I'd have that problem I'd come back the next day and it works fine. It's been a couple of days and the fans won't come on still. And it's quite warmish where I am. I had a look at Tore's website and according to my symptoms I should check the fuses. All the fuses are still intact. Any suggestions?

x98boardwell

Continue to diagnose through Tore's info. May have to do testing on CCU. Good luck.

ToreB

I guess you do not have any of the CCU buttons pressed while observing this. Are the fans behaving like this independently of the temperature setting? If the fans work fine on minimum temperature you probably have a problem with the rear fan, its resistor or relay.

This could be a failing fuse holder in the fuse box, not uncommon in 964's. Try wiggling these fuses: Fuse 1, (Terminal 30) Fuse 17,(Terminal 15) Fuse 28. (Terminal X)

It could also be a failing fan speed potentiometer in the CCU. I have seen several of these before, it can be fixed by someone with some experience with a soldering iron. Try wiggling the fan speed **** to see if this is the case.

Cheers,
Tore

StopLookGo

I hope I'm being clear. The fans I am referring to are the blower fans inside the cabin. I've pressed different buttons and this hasn't changed anything. I have also gently pushed and pressed and wiggled the fan speed ****, also nothing. I will try to move the fuses around to see if this works.

Earlydays

I've experienced the cabin fans not working at all and it was a blown fuse (in the engine compartment) for the rear fan.

onevoice

I had the same problem, it was the final stage amplifier. It had corrosion inside. Not sure how to check it electrically, but it's easy to take off and take a look inside.

StopLookGo

Just got back home after getting caught in a thunder storm. No ac. It brought back memories of being a uni student driving a barely functioning car. I popped the hood and moved pressed and wiggled the fuses and still nothing. The fan in the front left fender is working well and I have had my rear heater fan removed a whole ago since where I live is quite warm.

Which is the final stage amplifier? I think I'll have a look at that.

Duck

If you have the rear heater fan removed, do you have a jumper on the relay or a resistor to fake the CCU that there is still a rear heater. On my 1990, I have to have a jumper on the rear relay (my rear heater fan is removed) or the fans will not work.

StopLookGo

Duck,

any details on how to do the jumper process? I've had my heater fan removed for a while now (over a year ago) and my ac was working fine. Perhaps my mechanic already did the jumper mod?

Duck

If you have been running fine for a year, then probably not the issue then. Still for information only, here is a thread with a couple options for the bypass wiring:

https://rennlist.com/forums/964-foru...ss-tube-3.html

StopLookGo

anyone have a part number for the final stage amplifier handy?

StopLookGo

we tried swapping out my CCU with a spare CCU from another car and have singled out my CCU as the problem. It looks like the CCU has been repaired previously. Anything I can test to try and repair this thing again? What would be the more common bits that fail?

StopLookGo

ToreB

There has indeed been going on some soldering in there. In my opinion, it is not of the best job quality, but it might be working OK. I have never seen problems in the PWM main fan speed outputs before, there are a couple of transistors involved. It could also be the main blower feedback circuit that makes the CCU to stop the fans. I would start with checking the fan outputs with an oscilloscope, (yellow/green and yellow/green wires) as well as the feedback circuit with a voltmeter. (green/red wire) This can be done in-car.
I have a full test bench for the CCU and can help with any repair if needed.
Cheers,
Tore