Timspu

I have a strange issue i hope someone can shed some light on.
On initial start up of the car i select max on the temp control and the footwell blowers work for about 20 seconds then switch off. If i select zero wait a time and select max heat they work again and then switch off.
I removed the centre console and found that the when the servo contacts the micro switch this appears to remove the power to the blowers.
Does anyone have any idea why this happens?
Is there something silly like a diode in the system which removes power from the servo but maintains power to the blowers.?
I have checked the in car temp sensor as per the manual and it works fine.

Any info would be appreciated as i don't have any info on how the system works.

Thanks

TIM

JFairman

My '87 started doing the exact same thing this winter. I rigged it so the fans would come on and stay on once the heat diverter valves were pulled all the way open by bending the thin metal tang that swings over and contacts the micro switch away from it a little and that stopped it from turning off the blower fans.

I've rarely needed the foot well blower fans this winter but it's real nice having them work again when I do.

Timspu

I was thinking of doing that but was not sure if power would be kept on the servo which could burn the motor out. When you bent the leaf did the servo stop by it self Any idea of the issue?

Cheers

Tim

JFairman

If you look closely there are two micro switches in there next to each other. Maybe the other one turns off the servo motor at the end of it's motion.

It was a couple months ago when I took it apart to see if I could do something to make the foot well blower fans keep running and I don't know how the whole auto heat thing works electrically.
I wouldn't fix it if the circuit board got problems. I don't like it and it's an over engineered obsolete piece of junk.
When it does goes bad it will go in the trash and then I'll backdate it to the old emergency brake with manual handle(s) to open the heat diverter valves.
Then put a fan speed switch in the dash where the autoheat interior air temp sensor vent is to the right of the steering column.

paulleslie

Hi
I had a similar problem ,if you study the wiring diagram there is a sensor located in the cooling air ducts. The wire from this comes into the car under the carpet on top of the transmission tunnel in front of rear seats .
Cutting the wire removes the sensor input to the autoheat box which cuts the fans off until the car warms up.
If sensor is bad the fans power up normally ,also check the 25a fuse under the front hood ,just incase.
This sensor is a bit of overengineering,
Let me know if this works.
Paul

paulleslie

PS
My wire had a white covering.

Timspu

paul,

i actually disconnected that sensor from inside the box and it made no difference. When i measured it at the connector it was open circuit.
I think the main issue is that the servo is driving to full hot and contacting the micro switch which removes the power from the servo and the switch. It appears the feedback from the cabin temp sensor is not having any effect. i have warmed and cooled the sensor , its resistance changes but the auto heater does not respond.
So i think i have one main issue which is no temp control as the servo goes to full hot. I have checked the Pot in the heater which is set right , the Temp sensor resistance is correct. So scratching the head at the mo.
All blowers work until the microswitch is contacted and shuts the blowers down.

HELP