Hi all. I've been away a couple years but am back in Houston,Tx and looking to give my 1992 964 C2 CAB some much needed attention.
To start my A/C - heater blower is running intermittantly. The local dealer here suggests the rotary fan control on the control module on the dash board is about to go out and has quoted a price for the part of $2000 uds. Seems a bit steep so I was looking for methods of verifying the control module was the problem and if so a source for a good used part.
Bruce

 

Bruce,

As per my Yahoo Groups reply, we need a bit more information. I can't tell from your description if you are talking about the dash blowers (there are 2) or the condenser blower in the left front wheel well. An intermittent condenser blower is usually the sign of a corroded ballast resistor (mounted on top of the condenser) and is likely to be no more than a $60 fix. Intermittent dash blowers can mean a blown fuse for the rear blower (in the engine compartment). Just a new fuse needed for that one. The CCUs do sometimes fail - but it's pretty rare. The problems are often elsewhere.

Regards

Dave

 

Dave:
Thanks for the help.
There are two rotary switches / dials on the control unit. One that
controls fan speend and one that controls temperature in the passenger
compartment. The fan speed control has to be joggled a bit from time
to time to make the a/c fan blow cold air into the passenger
compartment. Since the fan seems to be working when I get the switch
in the correct position it seems the switch has a bad contact on it.

The dealer here says the fan speed dial cannot be replaced. The entire
control unit has to.

 

Bruce,

Are you absolutely sure the problem is with the rotary switch?? I've not heard of anyone else with a similar problem. I just wonder what happens if you just turn the **** to, say position 3 - and wait. Don't turn on the a/c - just see if the fans come on. If you turn the heat control towards the red dot you should hear the rear blower come on. If you DON'T hear the rear blower come on there may be (almost certainly) a problem with the blower or the fuse. If the rear blower fails to start the front blowers will not run - regardless of whether you fiddle with the switch.

If the problem really does turn out to be the switch, you are correct in that the switch is not available separately - it's an integral part of the CCU.

Hope that helps.

Regards

Dave

 

Dave:
with a/c off the front fans run and continue to run as I increase the temperature to the last setting before the red dot. When I move to the final position . red dot the front fans shut down and the rear fan starts up. After about 5 seconds the front fans start.
Sounds like the fans are working properly.

thanks;
Bruce

 

Otto's in Venice CA will re-build the control unit for a reasonable price if you need

 

Bruce,

The rear blower should start as soon as the temp **** is moved off the blue dot. It should run at slow speed - if it doesn't, your ballast resistor is shot. It sounds like the rear blower is coming on only when it's high speed is selected by the CCU, i.e. when the ballast resistor is bypassed. It's a common problem. A replacement (and updated) resistor is available from your OPC for a few dollars. It's mounted in the output plenum from the rear blower - it just clips in on the left hand side right opposite the electrical panel.

Regards

Dave

 

If it is actually in fact the "rotary fan speed control" inside the head unit, you can get that exact repair done for $600 USD at SYSTEMS CONSULTING in Manhatten Beach, CA. I just did it on a 993.......

http://www.systemsc.com/index.html

 

I believe I see the resistor. A flat object on the side of the plenum I should be able to remove the leads and check the resistance. To remove it, it looks like it is best to remove the plenum to get at it and avoid breaking something.
I'll give it a try.

 

The updated resistor (that you might already have) has a, "manually resettable bi-metal thermoswitch which stops current flow to the first stage of the blower motor if a fault occurs in the blower motor circuit."



If this blower resistor bi-metal thermoswitch is tripped, it must be manually reset by pressing down the spring plate which is under the copper colored reed contact. And then you have to figure out why it tripped.

 

Hmmm...what I am looking at doesn't have a coil on it like is indicated by the drawing Jason sent.

 

 

Bruce,

Maybe you've found the problem!!!

Dave

 

I hope so.
I'm traveling for a couple of days but will check into this on return.
Thanks everyone for your help

 

You may find it useful to know that the whole cabin control unit replacement costs around £1000 her in UK, but if your garage knows to ask, they can get it on an exchange basis via Porsche for half that, ie. £500. Of course replacement is the easy way out, a good engineer can probably fix the internal components for less cost still.