Air conditioning

[zook]

My truck was in a shop for about a month. When I got it back the ac is not blowing cold and previously would freeze me out. System was upgraded about 3 years ago with new components. Compressor is not kicking on. What is the best way to diagnose the problem. Not sure where to start? Fuse/relay or? Appreciate any suggestions. 1991 gmc 1500 thanks in advance

[Kudzupatch]

Use a volt meter, start at the compressor and work back to find where the power is (or isn't). Could be lots of things. But mind just developed a leak and lost all Freon. HP port was leaking, $4 part cost me and $40 of Freon.

[speedygonzales]

He may not be as lucky as you with replacement. If his system has not been changed, he is still using R12.

There are several things you could do starting with easy or free and going up to the complicated.

There are a few reasons the compressor is not coming on. Loss of signal to the clutch. Loss of pressure (which would also cause a loss of signal to the clutch) by way of a pressure switch or the clutch is bad.

Check the entire system for disconnected wires or anything that looks suspect.

Using a meter or test light, you could probe the clutch connector to see if you are getting a signal to the clutch. If you want, you could jump 12 volts directly to the clutch and see if the compressor works. Easily done by removing the clutch relay and jumping pin 87 to 30 in the relay socket with a spare piece of wire. If you look at the pins on the relay, they are marked with numbers.

If the clutch does come on when jumped, it's time to check the switches in the AC system. If the system is low on charge, the compressor will be prevented from running should the charge get low enough.

First thing to do is check all the hosing in the system for oil residue. Most likely at connections but could be in the middle of a hose as well. This would indicate a leak since the refrigerant contains oil. check any connections with oil residue for tightness.

There should be 3 switches in your AC system located under the hood. The one in the accumulator is the cycling switch. The one on the back of the compressor is the high pressure cut out. The last one is the low pressure cut out and I don't know for sure where yours is. It will be somewhere on the high pressure refrigerant line. The low pressure cut out is the one to jump and see if the compressor then comes on.

If the jumper causes the compressor to come on, it may be time to take it to a shop IF YOU HAVE THE ORIGINAL REFRIGERANT which back then was R12. If you do use R12, I hope you have a friend that has some.

If your truck was already converted to R134, then your job is much easier. Let us know.

[zook]

Thank you for your suggestions. I will give it a try. The system under the hood was all upgraded/replaced 3 years ago including the compressor etc. Was ice cold until it sat for a month. Think compressor is not getting power?

[zook]

Had a few minutes and there is no power getting to compressor. Will look at a few things in the next day or so when I have more time.

[irvan]

what's this truck look like? Lets see a picture.

[zook]

1991 gmc

[irvan]

Good looking truck

[Kudzupatch]

Originally Posted by zook

Thank you for your suggestions. I will give it a try.

If like mine, it developed a leak the compressor will not have power. Be sure and check and see if the low pressure switch has power to it. If it does have power, it could be low Freon or the switch is bad. I am betting you have a leak and no/low Freon.

Mine developed a leak at the high pressure port and lost most of the Freon very quickly. Just replaced it and I am Vacuuming the system this morning so I can recharge it.

[zook]

Thank for your replies found wire unplugged this morning all working and back to ice cold again. Was just too hot for me yesterday heat index was like 107° just don't do well in the high heat and humidity

[Palf70Step]

Glad to hear you found the issue!