temp control fan speed
 

I have a 1986 porsche 944, my heat/AC fan will only work on the highest setting. what can cause this?

I've trying to figure this out myself.

1) it could be a bad fan relay.
2) it could be a bad fan motor
3) it could be the resistors. Check for corroded wires. The resistors are located behind the battery
4) in my case it was my radiator somehow failing to get the thermo switch activated.

Also check the coolant temp sensor and the DME Temp sensor in the block.

But i'd start with clark's to trouble shoot.

Clark's Garage Home Page

Fan speed easy fix
 

Hi terrylyn,
Here was the fix on my S2 last spring for what you are describing: Locate the series resistor 944-616-101-00-M100 above firewall ahead of windshield. Unplug wiring and remove. Soak it in vinegar for a couple of hours. Give it a good tap water rinsing and a little gentle bow dry, reinstall and enjoy all fan speeds again. Let me know how it turns out.

P.S. - I believe I split the body of the unit open to expose the windings before soaking.