CCU buzzing noise with key turned off?

[E36S50]

There is a strange buzzing noise coming from the CCU area of my '90 964's dash after the ignition has been turned off and the key is out. It continues to buzz for at least five minutes aftere the car is shut off but the noise is gone when I come back after an hour. So far it hasn't killed my new battery.

Has anyone every had this problem before?

While on the subject, I can get hot air to the center vents but the windshield and side vents blow cold. Is this one of the infamous "servo" problems?

Thanks

[gizmofixer]

Yes, the CCU buzz is normal, it will do this for a varying amount of time, sometimes just a minute, sometimes 15-20 minutes, temperature related.........
and Yes, its most likely a servo problem with your dash vents, good luck playing with these pesky critters!

[Don Settergren]

The is a small fan on the back of the climate control unit that runs nearly silent for 10 minutes after turning off the key. It is an easy replacement that might have been explained somewhere in the forum. I know I received help when I started a thread looking for a replacement when mine started to rattle.

[TCallas]

Most likely, Don is correct on this. There is a small intake fan mounted on the back of the climate control unit/assembly that sucks interior air into the climate control unit NTC-II (Negative Temperature Sensor Coefficient #2) sensor to tell it the interior air temperature and adjust accordingly. I assume this is to cool off the NTC-II sensor inside the climate control unit itself once the car has been shut down.