Modulating HVAC fan on 1989 964 C4

[pracine964]

Hey there,

When I turn on the HVAC fan, the speed of the fan varies by itself and sometimes it doesn't work at all for sveral minutes, then goes on for a few seconds. Could it be an electrical problem? Is there any quick fix or should I take it to my mechanic? Thougt I've read alot on the 964 problems that I could encouter with my baby, I never read about this behavior. Any Help?

[lucittm]

Several possibilities (of course!)

1. The HVAC control system contains a thermostatic switch, they wear out but not often.
2. The blower motor has numerous connections, they can oxidize or vibrate loose and create an intermittent connection.
3. The bearings in the blower motor are almost gone. Usually accompanied by a squeal or grinding noise from the motor in question.

I would check all the connections including the appropriate fuse and relay. Then check to see if the motor is making any noise especially when starting and stopping. Are there other blower motors in your model? I have four in my car. Are they all running together? Lastly, you could swap your HVAC control unit with a known good one and see if that cures the modulation.

If all else fails the dealer can repeat the steps above at the shop rate, install several parts you don't need, and then tell you he doesn't have the motor in stock.

Good Luck,
Mark

[pracine964]

Thank you Mark. Well appreciated advices. I realaized I did not mention my car is a 1989 C4 coupe.

Thanks again.