View Full Version : Heater fan on high constantly

02-20-2017, 12:16 AM
I have a 91 SC with the auto temp control and it has just started running the fan on high constantly even in the off position. Any ideas?

02-20-2017, 12:51 AM
For my 1991 XR7 with the auto temp control, it was a shorted pass transistor on the speed control unit.

Hint: When you pull it, if it's rusty and you've never changed the heater core - CHANGE THE HEATER CORE.


02-21-2017, 05:47 AM
That is exactly whats wrong I had them fail on both of my birds

02-21-2017, 09:06 AM
They are still available; well, actually, the improved later model ones are.

Not cheap, though; $128 and up quickly at RockAuto: http://www.rockauto.com/en/catalog/mercury,1991,cougar,5.0l+v8,1198672,heat+&+air+conditioning,blower+motor+control+module+/+resistor,6557

Edit: RockAuto doesn't show the TBird on the list for that unit; however, it's the same and fits the same. That part's not one of the Cougar-specific parts.


pro street rich
02-21-2017, 03:27 PM
I just stripped out a 90 that had good control's in it if you want?? ....Rich