Defrost Button Activates Cooling Fans?

[OK-944]

To follow up my earlier blower-motor related post (where this motor did not work, so I cleaned its relay contacts, heard the motor work momentarily, then its fuse blew out) I have noticed that when I push what I call the window defrost button (just under the cabin air recirc button) the cooling fans come on (the cooling fans also come on with the A/C switch, which is normal).

If my memory serves me somewhat, I remember that the defrost switch would activate the blower motor and also send lots of heat to the windshield - sort of a "super heat-defrost" mode. My car is an 85.5.

Basically, I'm wanting to trace the blower-motor gremlins so I can get some forced heat into the car as the weather gets colder - and the window defrost is very important in Vermont.

...but is the defrost button supposed to activate the cooling fans? Maybe the P.O. messed with the wiring? Comments? Thanks!

[Porsche-O-Phile]

It's normal since defrost runs the a/c compressor.

Don't sweat it. The car will warm up just fine. I always warm mine up until I've got plenty of heat anyway - who wants to get into/drive a cold car? Get a remote starter if you must (but put it in neutral! The starter is torquey enough to move the car if in gear)

[AaronM]

Originally Posted by Porsche-O-Phile

It's normal since defrost runs the a/c compressor.

Spot-on. The reason for this is that running the A/C removes humidity from the air inside the cabin as well, which plays a big roll in defogging the windshield.