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Join Date: Aug 2003
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No Heat in 85.5 NA

Restoring 85.5 and I am having trouble working out a heater problem. The heater valve is ok but vacuum will not shut off. I have checked the temp. sampling system. The blower pulls cabin air over the temp sensor. The little solid state sensor is clean. The little blower works when the heater blower is running.

Are there other places for electrical failure?

Could it be the Vacuum valve is stuck open? If so where is this valve located?

Old 10-16-2003, 03:24 PM
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I have not yet seen the vacuum valve get stuck, but its bolted to side of the climate mixing unit. Pull the glove box out and look to the right, there are two vacuum valve units, one of them is for the heater valve.

You can check for voltage to the valve while turning the temp indicator. Also I still would not rule out the smapling unit, you need to make sure that the resistor is working.
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Old 10-16-2003, 04:09 PM
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yea, checked out the RTD. 2+ M-ohms when I put a flame to it.
Old 10-16-2003, 05:11 PM
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Worts case scenario would be a problem with the climate control head unit. I lost one on my 85.5, the air dam sliders did not work at all.

Best case would be either the vacuum solenoid, or possibly a broken vacuum line behind the glove box.
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Old 10-16-2003, 05:27 PM
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looks like the control unit or (unlikely) the temp pot on the dash. Manually energized the vacuum valve & got heat.

anyone had any success in rebuilding this controller? figure its just the PNP power transistor. IF no, where can I get a rebuild?
Old 10-17-2003, 05:30 AM
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Usually there is someone on Ebay selling a used head unit. But 944Ecology.com seems to have about the best price around.

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1980 911 SC
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Old 10-17-2003, 11:27 AM
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