The '68 300 has strange issues with the heater fan and a/c compressor

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The heater fan on this car seems to turn itself on and off, accompanied by a noticeable "click". I have already been sitting in the car listening to the radio with the key in the "acc" position and the "off" button pushed on the heater control and I hear a "click" and the fan turns on. Other times I have been driving down the road with the fan running even though the "off" button is pushed in then I hear a "click" and the fan turns off. Also the a/c compressor just runs in every mode, even "off". The heater control switch is brand new. Any thoughts?
 

jct

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You could always pull the fuse out temporary
Screenshot_2019-07-06-19-40-24(1).png
 

Davea Lux

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The heater fan on this car seems to turn itself on and off, accompanied by a noticeable "click". I have already been sitting in the car listening to the radio with the key in the "acc" position and the "off" button pushed on the heater control and I hear a "click" and the fan turns on. Other times I have been driving down the road with the fan running even though the "off" button is pushed in then I hear a "click" and the fan turns off. Also the a/c compressor just runs in every mode, even "off". The heater control switch is brand new. Any thoughts?

Is this car standard air or ATC

Dave
 
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It's the standard air, not the ATC. I actually have the factory service manual and have been studying that diagram for days. I just can't see what could be wrong. We were planning to get out the voltmeter and try figuring this out, but I figured I'd ask since there are some odd components in this system (like a vacuum switch, time delay relay, temperature sensor) which I'm not really too familiar with. I especially can't figure out the purpose of the temperature sensor since this is not the automatic system.
 

Davea Lux

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The time delay and the temp sensor are unlikely to be the source of the problem you are having. Both of those units are wired after the power source from the blower motor switch and the push button vacuum switch. I think you have a bad push button vacuum control. This is by process of elimination as the blower switch should be disabled with the push button vacuum switch in the off position.

Dave
 

Davea Lux

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Try disconnecting the electrical leads form the push button switch. With the button in the off position run a continuity test between the two terminals. I should not show a completed circuit.

Dave
 
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Thanks for the replies. The vacuum push button switch is brand new. I suppose it could be bad right out of the box but is that likely? Also, the blower fan can run when the key is in the "acc" position. I think its only supposed to be able to run with the key in the "on" position. I would not be surprised if some previous owner hacked up the wiring. I will check the push button switch as you recommended, but I don't think I'm going to have time to do it before Carlisle. I've got a few other things that need to be addressed first.
 
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