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Discussion Starter #1
Starting to look at the AC on my 71 (factory AC)... All blower speeds and Vac/doors respond fine. Jumpered the Ambient switch no power on the light blue wire. Jumpered 12V to Compressor, engages fine, compressor is quiet, sight glass shows freon moving. When I put wiring back to normal, the anti-diesel relay does engage the compressor when I turn off the ignition switch. Where to next?? Any advice appreciated.
 

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Remove the Thermal Limiter from the plug, Follow the wires from Compressor back to locate it, Jumper across the two out side terminals,There should be power to it. If the compressor engages the limiter needs replaced.

I would have to look at a wiring diagram to go further.

Mike
 

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Discussion Starter #3
Thanks for the advice Mike, greatly appreciated!

I traced the green wire back from the compressor, but it does not seem to have a thermal limiter in the circuit. Some of my notes are showing they did not start putting the limiter in until '73? The light blue wire on one side of the ambient temp switch (which should be hot when the dash switches are set properly) runs back to the anti-diesel relay on the back of the dash. I have not taken the dash pad off yet, I hope to get to that tomorrow. I do know that relay is doing part of it's job because when I turn the car off, the compressor engages briefly to choke the engine as it should...

Thanks again, Mark
 

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i dont remember those old system to well .did they have a low pressure cut off switch .if so jumper it to see if the compressor comes on
 

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Discussion Starter #5
These years did not even have low pressure cut-offs. The only thing that protects the compressor in these earlier years was the ambient temperature switch.
 

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i wasnt sure its been at least 20 years since i have had to work on that old an ac system.they seem to work much longer than the new stuff.i remember the thermal limiters usually clipped to the compressor bracket or one of the compressor tubes.
 

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Discussion Starter #7
Yes, I thought it might be there. If there was one, it has been removed. I appreciate the feedback!
 

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Somewhere at my place I have a Pontiac shop manual for a 69 GTO, if I can find it I will look for a diagram, I would suspect being an A body they should be very similar if not the same.
I will let you know what I find, I also have all the manuals for my 72 Sprint and will look there also, I worked at a Chevrolet dealer from the mid 70's into the early 80's, I kind of remember thermal limiters on most models in that time period, time does take a toll on memories though.

Mike
 

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Discussion Starter #10
Thanks to everyone for your input! The blue wire not having power across the ambient temperature sensor (last stop on its way to the compressor via the green wire on the other side of the sensor) is taking me into the back of the dash which I have not opened up yet. I do know the light blue wire leads back to the 2 relays on the back of the dash near the glove box. The 1971 has an anti-diesel relay and a blocking relay. As I mentioned in an earlier post, the light blue wire does get energized when I shut the ignition off - the anit-diesel relay does this to "choke the engine" with the compressor so that the engine does not run on... I need help understanding how the relays work together, and perhaps someone could tell me if the fact that the relay is "choking" the engine properly on shutdown means that the relays are OK and perhaps the problem is in the dash switches? All of my blower speeds work fine, but I never get compressor power in any position of the selector switch.
I did set up a temporary switch to put 12V to the compressor, and I get cold air when I do this. Although this is Air Conditioning subject, perhaps I should be posting in the electrical forum, sorry, I am new at all of this...
 

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Discussion Starter #11
I have found part of the problem. The blocking relay on the back of the dash (next to the anti-diesel relay), was burned up. I have replaced both of those relays, and I now get power to the compressor in the proper switch positions. However, now I have lost my high blower speed. All other speeds are fine. The high speed relay was working before. Not sure what is going on now. I am going to disconnect the battery and start checking and cleaning all connections first...
 

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The High speed has a in-line fuse near the fan relay. Also check for a bad connection at that relay. Close to the evap. case on the firewall.
 
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