Damn blasted HAVC control

beetos · 04-04-2002, 08:31 AM

On my 90 964, if I have my temperature turned to full cold, the blower works ok, as soon as I move it off cold to say, medium, the blower quits after a few seconds. Is there a way to provide power to the blowers independent of the position of the temp know. These control units are about a grand so I'm not giving up without a fight!

jlui · 04-04-2002, 09:29 PM

Same thing happens to my 1990 C4. Correct me if I am wrong, but I think the car has a temperature sensor in the compartment. It will shut itself off temporary until the interior temperature rises above the temperature you adjusted to, then it will turn back on.
For example, full blast cold air is at 18, you then switched the controller to 24. To save energy, it will shut air-con off to bring the interior temp up naturally rather than blow warm air. Once the sensor measures compartment temp is above 24, it will restart itself, blowing cold air at 24.

Just me guess.

Planter91C2 · 04-05-2002, 07:34 AM

i think that is right. i'll re-check but i believe when the temp. dial is turned the fan is contolled automatically to achieve the desired temp.

d_boyce · 04-05-2002, 08:57 AM

The symptom you describe is due to the engine compartment mounted blower fan not running. A very likely cause is that the slow-speed resister mounted in the blower outlet tube has gone bad. Could also be a fuse, relay or blower motor problem.

-doug

beetos · 04-06-2002, 08:10 AM

Doug,
I think your onto somthing!
I removed my engine mouted fan to install the supercharger conversion. There were a couple of connections on the outlet tube which are now disconnected, one to a probe type sensor in the tube and one to a bi-metalic strip looking type connector with loose spade connectors (also in the tube). Which one is the low speed resistor you are referring to? Appreciate any further help.

d_boyce · 04-06-2002, 07:25 PM

The slow speed resistor is the thing with the spade connectors. The other "probe" thing is a temp sensor.

There was a recent thread on the rennlist.com forum that described what was needed to get the HVAC to work correctly without the fan and sensor in place. It involved connecting a 50 ohm/15 watt resitor in place of the fan motor so that the HVAC controller thought the fan was running.

-doug