AC Blower runs well but only when directly connected to battery, what might be the problem?

[pit]

AC Blower runs well but only when directly connected to battery...same happens with cool air blower motor...fuses are ok...how can I see the wiring diagram for my 911 1987 Carrera...what might be the problem?
Thanks

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: Air Conditioning on the 911 - 911 (1965-89) - 930 Turbo (1975-89)

[Nick at Pelican Parts]

You either have a bad blower motor switch or more likely a bad blower motor resistor. This resistor drops the current to the motor so you can change the motors speed. Try replacing that first

- Nick

[wwest]

Originally Posted by pit

AC Blower runs well but only when directly connected to battery...same happens with cool air blower motor...fuses are ok...how can I see the wiring diagram for my 911 1987 Carrera...what might be the problem?
Thanks

__________________
This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: Air Conditioning on the 911 - 911 (1965-89) - 930 Turbo (1975-89)

Assuming you are talking about the evaporator blower there is a voltage limiting resistor module that limits the blower voltage in the lower speed control positions. But these are bypassed in the high speed position.

BUT...

The "module" also has an overheat CB should the resistor pak begin to overheat. If the CB fails "open" the blower will not run.

Worth an inspection, mounted in the evaporator airflow inlet behind the passenger footboard.

Sometimes fuses are good but not tightly clamped by the holder.

[ghiaholic]

I had the same thing. After tearing my hair out chasing the entire circuit with a tester it turned out to be that the yellow wire out of the relay in the smuggler's box was disconnected. This goes to ground when the starter is not engaged - you need continuity to ground with this wire for the blower to run. Reconnected the yellow wire (PITA working under the dash behind the vents!) and it runs like a champ.