Auto heat system

[Jkershaw356]

Hello

I have an1988 carrera with the auto heat option. The system was functioning normally until yesterday.

Now if I have ignition on without the car running- no heat.

The heater blower in the engine does not turn on at any auto heat number (0-9/defrost)

I tested the blower motor and it runs normally

I looked at the engine compartment blower relay

-the fuses are intact
- i have power to terminal 12,7 and 8
if i jumper 7 or 8 to 5 or 6 the blower motor runs

My questions are
What triggers the rear blower motor to turn on when the auto heat unit is switched from 0 to 1?
is there a way to determine whether it is the engine compartment blower relay or the autoheat microprocessor that is faulty?

Thanks

[86 911 Targa]

Originally Posted by Jkershaw356

Hello

I have an1988 carrera with the auto heat option. The system was functioning normally until yesterday.

Now if I have ignition on without the car running- no heat.

The heater blower in the engine does not turn on at any auto heat number (0-9/defrost)

I tested the blower motor and it runs normally

I looked at the engine compartment blower relay

-the fuses are intact
- i have power to terminal 12,7 and 8
if i jumper 7 or 8 to 5 or 6 the blower motor runs

My questions are
What triggers the rear blower motor to turn on when the auto heat unit is switched from 0 to 1?
is there a way to determine whether it is the engine compartment blower relay or the autoheat microprocessor that is faulty?

Thanks

I believe it is the Auto heat relay in the engine compartment.

Or, the control rod is broken.

[86 911 Targa]

[T77911S]

if the foot well blowers come on the controls are ok.

the rod does not matter. that just closes the heater flappers.
the cam on the controls is what turns one the fans , and closes the flappers.
once the cam fully rotates and closes the flappers it makes contact with a micro sw that provides power for the fans.
(just form memory which is not so good these days).

[ant7]

Its often the electronic relay in the rear left of the engine bay thats the culprit!
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