automatic heater control
 

My 79 SC has been recently reconverted from "header" to "heater." However, the blower motor will not run unless I jumper a hot lead from the fuse block in the engine compartment.

I followed the testing procedure for automatic heating control in the factory manual. The lever lifts as it is supposed to, and the resistances of the two sensors (undercar and inside car) are within tolerance. The power leads for the control unit show voltage.

Is the function of the undercar sensor to prevent blowing cold air until the engine warms up? Is this the most likely cause for no power to the motor? How do I check the relay in the engine bay?

Finally, can I solder in a resistor (which?) in place of the engine sensor, or jumper the leads altogether?

Thanks everyone-
Closer to heat in Chicago!

From your closing comment ("Closer to heat in Chicago") it sounds like you don't have any cabin heat now. If everything is back to stock type heat exchanger setup, your Porsche should be heating the cabin with no problem even with no engine blower moter.

Apparently a lot of SC owners have disconnected their rear blower motors due to the failure of blower moter itself. My 81 ROW SC blower motor is in this catagory as well. There are quite a few message threads that discuss whether or not the blower motor is necessary at any engine speed other than idle.

When I dropped the engine to R&R the clutch arm a year ago, I refurbished both of flapper boxes and adjusted the cables for the auto heat. There is no lack of heat with no engine blower motor.

Are you getting any heat to the footwell and/or the dash now?
Since you said the auto heat control is functioning and that the handle (below the hand brake) is rising, then the flapper box "shutters" should be closing through the action of the cables.
If the "shutters" are closed then there should be plenty of hot air flow to the cabin.
When the engine was converted back to heat exchangers, did the tubes that run from the fan/shroud get properly replaced?
Have you checked the dash linkages for their various settings? I think even if they were totally out of proper adjustment, heat would be appearing in the cabin.