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Recommended Posts

I have a 1995 993 with a heating question. Since i have owned this car, i have never really had the best heat in the winter driving months.

I purchased an OBD Porsche test tool that turns on the fans, opens flaps, etc...

this tool is very useful, and when using it to test the HVAC, everything seems to work.

My next experiment involved checking the differential pressure valves that sit underneath the engine and divert hot air underneath the car or to the cabin of the car if the heat is selected. these metal flaps seemed to move freely and i don't think they are of concern.

I did find one of the silicone 90 degree hoses that connects to the top side of the heat exchanger was cracked. i thought i found the reason why the cabin wasn't getting warm. but, after letting the car heat up driving down the road, i still had very little cabin heat.

I have also noticed that with the cabin fan at position "1" it seems to be fairly warm. but once the fan is at position "2,3,or 4" the air seems cooler. i haven't verified this with a thermometer, but i think i am correct.

so i started looking at heat exchangers. On my car, I have, I guess, what is referred to as "Gillet" heat exchangers. i don't know if these are installed from the factory or have been installed after the fact. I couldn't find anything that confirms that Gillets were installed from the factory. But comparing the heat exchangers made by "Bischoff" to the one's made by Gillet, the Bischoff are larger and look as if they are more efficient at performing heat exchanger duties. The Gillet heat exchangers have what i would guess is a smaller size and less heat transfer to the pipes that route to the cabin of the car.

I'm wondering if i am on the right track, and if the Gillets that are installed on my car are the primary reason i have little cabin heat?

Also, on a related side note, when heat is selected, the mixing flaps under the front hood open the doors for heat to enter the HVAC system. does the fresh air intake at the rear center of the front hood have any valve that should be opened or closed, or is there one?


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