78 Chevy K10 AC problem

[DSS]

My 78 Chevy K10 Pickup has the stock AC which typically works fine- Around this time last year, it abrubtly quit blowing cold air. I went to check it out a few days later and it has cured itself and worked fine... A few days ago, the AC again abruptly quit blowing cold air, but now it hasn't fixed itself- I am by no means an AC expert- Does anyone out there have suggestions on some things I should try to check before I bite the bullet and head to a shop?

Thanks!

 

[chengny]

The best place to start would be the compressor clutch and then work backwards from there.

Set the HVAC controls to MAX AC, open the hood and observe the clutch plate on the front of the compressor. It should be pulled in and spinning right along with the drive pulley. This shows an R4 (pancake) type compressor - you might have an A6 style but the clutch is in the same place.

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Turn the AC off and on a few times and note whether the clutch plate pulls in and starts spinning when cooling is called for.

This is an A6:

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Come back and someone will help you with the next step. Do you have a multimeter?

 

[DSS]

Hi- Thanks for the reply- I checked and it appears to be an A6 type compressor, and no the clutch stays still when the MAX AC is selected. Do not have a multimeter

Thanks

 

[chengny]

That's okay, we can probably figure it out without a meter.

Since the problem is intermittent and the system works fine - when it works - it is most likely a wiring connection issue.

Might as well start checking connections at the compressor. Look around in back of the drive pulley. You should be able to locate the wires that energize the magnetic clutch. Follow them to the end - where they attach to the compressor. There will be a female plug. It most likely will be this type:

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Pull it off the male stabs. The connection point can be in several different spots. But if you just trace the power leads it will be easy to locate:

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Make sure the ends of the wires are securely fastened to the sockets in the plug and that the male stabs on the compressor fit tightly into the sockets. If everything looks normal, push the plug back on and try to operate the clutch as before.

You don't have a test light do you? Even a test jumper would be a big help - got any scrap wire laying round to make one? It doesn't even need to have terminals on the ends, just needs about an inch of insulation stripped off.

 

[DSS]

I cleaned the contacts from the clutch to the firewall connector- found the low pressure control switch and cleaned that connection too and the old thing started working again and blowing cold air!-- Thanks for the help!

 

[chengny]

Good for you - the low side control switch was going to be my next suggestion.