neversinksmith

i was getting nice hot air for the last six mths since i got the car. lately i noticed that at full hot setting the heater was only putting out pretty warm air. i was driving home in the rain last night and the windshield was fogging up so i pushed defrost button and within seconds i had supper hot air coming out of the vents.

NOTE: the defrost and a/c buttons have both malfunctioned where they work when depressed but have to be held on to continue working.

when i let off the button the air goes back to warm.
clearly i need a new hvac control module but do you guys think this is something else?
ive blead the cooling system several times and the car is cooling itself properly

Zirconocene

Vacuum leak somewhere in the system?

voodu3

I would guess you have mixing flap or a temp sensor not function properly. There is a lot of good info on the system on Clark’s http://www.clarks-garage.com
I used it to find that my temperature sensor wasn’t working.

neversinksmith

Mixing flap is moving all the way open and closed w the temp switch adjustment. Just checked. I can hear the interior temp sensor fan working.
i do have a bungh of rags and gloves in glove compartment. They were covering the vent that the hose goes to in glove compartment. Would that have anything to do w it?

neversinksmith

Does interior temp sensor need periodic cleaning?

jeyjey

Shouldn't, unless the little plastic grill gets completely clogged.

neversinksmith

Why super hot w defroster but not so hot w regular heat?

Zirconocene

On the 928 (I've been reading about this, no direct experience) the system is set up to bypass a lot of the electronics when things are set to full stop positions, like you might get with a defroster, but not with regular heat (meaning somewhere in between the temperature range).

I don't really know how well related the systems are between the cars but if I had to bet a nickel, the same thought process lies behind how each model works.

ETA: This is a different issue than what you're dealing with but there's some good background information on the HVAC system in the thread that might be relevant to what you're looking for: https://rennlist.com/forums/928-foru...in-motoin.html

Good luck