bpp944

The heater on my '89 3.2 seems to turn on whenever it wants regardless of the ambient temperature inside the car. The fan switch between the seats doesn't seem to work at all either (it's a three speed fan). I removed the fan switch from the car and am suspicious of the potentiometer which is part of this assembly.

Has anyone had a similar problem? Thanks.

H. D. Smith

I have had the same issue, so I added a switch to the unit that allows me to cut off the main blower when not needed. Below is a picture of the switch and it's location. It's not a perfect fix, but it worked for me.



<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Tom F

I have had similar problems on my SC's, which have a similar, though not identical, automatic temperature controller. There have been two causes: the potentiometer in the temperature controller and the temperature sensor itself.

The temp controllers fail because Porsche used a cheap potentiometer (wound wire) in the unit. Luckily, you can take apart the temp contoller, once you remove the box from in between the seats. I've replaced the potentiometer in my car with a high quality commercial (carbon pile) unit. it works great, though I had to fiddle with the indicator, at first, to get the settings right. It's a 0 - 2,000 ohm unit, I believe - not a size that my local electronic supply carries, so I had to order it.

I think that you will find the temp sensor behind the dash in your car (there's a little disc shaped aperture where air is drawn in over the sensor by a little fan). On my SC, the sensor is mounted near the rear view mirror. However, you can test the sensor when you have the box out by putting an ohmeter across the connector at the temp controller box. Then, blow on the sensor. They're really sensitive, so just that temperature change should register, and quickly, too. The service manual says what the resistance should be at normal room temperature.

One other failure mode occurs to me, but I have not actually seen it happen. You should find that there are two, very small switches within the temp controller, one for the full on position, one for the full off. Maybe, in your car, something has gone wrong with these switches. However, they are independent, so I think that you'd have to have them both fail in order for the heat to be full on when the temp controller is pointed to "0."

bpp944

Tom, thanks for the info. I took a closer look at the potentiometer last night, it looks and smells like it got fried. I picked up a replacement unit (the entire console) and plan on installing it over the weekend.

Tom F

You're welcome. However, I should correct one point from my earlier post. I used a "plastic" potentiometer, whatever that is, not a "carbon pile" type. The plastic unit was the most expensive type in the catalogue, and had something like 10 times the life expectancy of the lesser units. This brought the price up to a whopping $6, or something like that.

bpp944

O.K., So I replaced the console between the seats over the weekend, this cured the bad fan switch and potentiometer (which was indeed fried), but has not stopped hot air from entering the cabin from the passenger foot-well.

I'm told that the cable operated baffles for the heater have been known to get stuck (and knowing that my car is from NY), I'm thinking that I need to take a closer look at the passenger side heat duct. Any ideas?

Tom F

Yes, they could be stuck - they rely on springs to go to the closed position, so it could be a broken spring, too. They're no fun to get at. You have to have the car up, and then they're still tucked away. Don't try to remove them without soaking the studs with penetrating oil for a few days - you'll snap the studs, and then you'll really have a problem. I have never had a valve stick, but if I did, I'd check the springs first, then squirt some penetrating oil everywhere to see if I could get them free. By the way, you will smell the penetrating oil inside your car, if you get it into the valve. Also, the valve pivots on plastic bushes, so it should not be too hard to free up, if stuck.

Did you try opening and closing the circuit with the temp sensor in it to rule out a faulty sensor? When mine failed, it failed in the "hot" position, and my heat wouldn't shut off.

bpp944

Tom,

I haven't had an opportunity to check the temp sensor as of yet, but will definitely check that before going under the car.

Thanks for the tips,

Bryan

Klax

Bpp, Have you found a fix? I seem to have the same problem, heat coming from passenger footwell at all times regardless of control settings. When I want heat I get from all the vents, but when my automatic heater control is off (on 0) I still get heat out of passenger footwell. Anyone else have this issue? I've got an 87 Targa.