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A/C Compressor power 1970 SS 454 Monte Carlo.


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I have a 1970 SS 454 Monte Carlo with air conditioning. It is all original and the a/c did work. The compressor started to make noise and since it is very old ,possibly the original I will be changing it. NOW for the problem. On this vintage GM the control panel when switched to Defrost, A/C or possibly Bi level the compressor is supposed to have power. It does. Where the problem comes in ,is that the power wire ( plugged or unplugged) for the compressor also started to come on in the heat zone as well. It will shut off in the OFF position , however I am quite certain the compressor wire is not supposed to have power in the HEAT position. I have started to work in the dash area , but I have not started to chase this problem yet. I thought I would ask the experts first. I am thinking there might be a relay stuck on , possibly when the compressor went bad ?  Your thoughts and advise please . Thank you in advance.

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Yes it does , however in the heating  range it should not have power. I have owned this car for 30 years and it was all good . Something changed around the time the compressor went bad. Thank You very much for your input ! One way or another we will figure it out. ( I Hope) Take care and thanks again .

 

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Although I’ve never worked on this thing, I think I understand how it works:

The top lever is the main control and has a switch that interrupts power coming from the blower switch.

The bottom lever has one more switch.

I believe for the compressor to get power, both switches need to be closed (contacts closed).

 

1970 AC.JPG

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Excellent diagram. Thank you , very much for taking the time to forward it to me. I will be digging deeper in the next few days and this will be a very big help.Thank you again.

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  • 2 weeks later...

O K. After studying the wiring diagram supplied by Paul Bell ( ThankYou !) I found that the cause of my above described problem ( A/C compressor coming on in the heat position) was caused by the micro switch being loose in the back of the selector panel. The switch that has all the vacuum lines coming out of it also has an eccentric on it's backside that hits a micro switch with two terminals and tree wires coming out of it . The switch is slotted for an adjustment with a very small hold down screw that also holds it in place. I cleaned and greased all moving parts and put a serrated washer on the hold down  as well. Checked it with a test light and SUPER DUPER works the way it is supposed to . Thank you Paul Bell for your help. Also , I hope this info will help someone else. Thank you all once again.

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  • 1 year later...

I’m having the same issue on my 70. The compressor runs when the selector is in the heating and vent positions. Now that I’ve found this post, I’m going to look at mine tomorrow and hopefully correct it. Anyone else had this issue? If so, anything else to look for? Thanks 

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Sometimes my compressor runs in the off position and I have to repeatedly move the selector lever from a/c to off to make it actually turn off. I have had that issue for a long time and never even noticed this thread. Now I have another fun project. :yay:

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  • 3 weeks later...

I replaced the blower switch today. I now have cold air on all speeds. A must for this NC heat and humidity. Still having the issue with the compressor running all the time, but it looks like I’ll have to drop the dash to get to the micro switch. I just didn’t feel like getting in to all of that today. Anyone ever replaced the micro switch? Are they available?

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