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No A/C light compressor not engaging

Tiny
CZR1760
  • MEMBER
  • 1997 CHEVROLET SUBURBAN
  • 175,000 MILES
I am trying to get my K1500 SUV AC working. When I purchased the truck, I new that the AC did not work. The previous owner told me that the compressor locked up, so he changed to the shorter belt and moved on. Now that I have moved to Florida, I need the AC. While changing out everything I found that the rear AC has been disconnected and the shared pressure hose obviously changed out. I bought all new parts (accumulator, compressor, condenser, low pressure switch, high pressure switch and orifice tube filter). Ia m not going to worry about the rear air, I will just be happy to have the front AC working at this point. Now that I have everything installed on the truck, I vacuumed out the system and it holds. The problem that I am having is that my dash light is not coming on and the compressor is not engaging. I checked and I have no power at the low pressure switch. Checked all fuses and relays, everything is good. I am not sure where to go next. I have read several things about checking the control head in the dash, which I may try next. This may also be relevant, the first and third settings do not work on my fan settings.
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Saturday, July 28th, 2012 AT 3:13 AM

15 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
It sounds like you lost power to the controller or the controller is bad use the guide to check for power input and outputs.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here are the air conditioner wiring diagrams (below). Please let us know what you find.

Cheers
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Saturday, July 28th, 2012 AT 3:22 AM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Yes. They just removed the original hose that split and installed one for the front only. I only installed a partial can before stopping for the night. If I were filling front and rear AC, the system is supposed to hold almost 5 lbs of Freon and 11oz of oil. Since I am only charging the front, I figure my charge should be much lower. Freon is not cheap and once I started to get some low side pressure to rise I stopped because the compressor did not engage. If the compressor does not kick on, my low side pressure is just going to spike up. That is when I checked the low side switch and found that I have no power to the switch.
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Saturday, July 28th, 2012 AT 3:33 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
I am going to be asking you a lot of questions so did you replace both hoses to the rear EVAP core to bypass the rear air? My main concern is the rear air was bypassed correctly. When you replaced the AC compressor did you do what is called a oil balance procedure on it? 11 ozs would be a full oil charge when only replacing part of the AC system you would only add part of that. Also, the compressor will not kick on fully until you add a couple of 12ozs cans or so a half of can is not going to kick the AC compressor fully. Also you replaced the drier condenser orifice tube compressor and pressure switch? You mentioned the compressor blow valve on the back of the compressor blew off the brass one? If so why did the AC compressor kick on and the pressure went too high and it blew off? What are your concerns with the control head itself?
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Saturday, July 28th, 2012 AT 4:16 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
I did not hook up the rear air hoses. The low pressure line is broken at the rear of the truck. I only jumped the AC relay because I have no power to low pressure switch. I assume that the cycle switch blew out because I did not have the snap ring all the way in. Or it blew because I put too much pressure on it while adding Freon, because it was not working properly.
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Saturday, July 28th, 2012 AT 4:23 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Alright you answered some of my questions the blow off valve both pieces screw in. AC do not see a snap ring. Also, just the can pressure without the AC compressor should not cause that valve to blow off. You need to replace that blow off valve if it blew off. My question is, so it is set up hose wise etc? Just like the system that does not have rear air? Both those hose going to the rear have been changed? Also, please answer the other questions AC asked you AC am flying blind here. The information you give me is all AC have to go on. Also, do not jump the pressure switch that is your safety to keep you safe and your AC system safe.
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Saturday, July 28th, 2012 AT 4:40 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Okay. I filled approximately 4 oz of oil into the compressor. The hoses going to the rear have not been changed, they are disconnected and not being used. I installed all new switches. Low pressure on dryer, high on top of hose on compressor and cycle switch in the back of the compressor, that is the one that blew out. I pulled the AC relay and jumped the connection to make the compressor cycle. No power at the low side switch and do not think I have power at the cycle switch either. I thought the head, because I read about transistor going out.
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Saturday, July 28th, 2012 AT 4:51 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
How much oil did you get out of the old compressor you changed? You are supposed to measure the oil you get out of the old compressor then put that much back in the new compressor. If no oil comes out you put in 2 ozs also if there was oil in the new compressor that should have been drained out. Was there metal in the AC system like the orifice tube etc from the compressor failing? You said the hoses are disconnected to the rear AC hope new hoses were installed to hook it up like it should be for a none rear AC system? The AC high pressure cutout switch on bottom rear of the AC compressor and the AC compressor cycling switch on top right of the AC accumulator. Those switches the black wires with a white strip go to ground that is why there is no power there switches. If you had power also you would have a bad short to ground.
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Saturday, July 28th, 2012 AT 5:16 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Let me ask, do I need to hook up the rear AC lines? Because I was not planning on it. They are currently disconnected in the engine bay. The low pressure line is broken at the rear of the truck where it goes through the floor. Can I just not hook the front using my existing hoses? Also, no oil came out of the old compressor, it was locked and fried, who knows for how long. I did not see any metal anywhere when I replaced everything. No oil in new compressor. And I am sure I lost half of the oil that I just put in when the cycle switch blew out. I am going to remove the compressor and re-install the switch now. I am pulling the compressor off, because I want to make sure that the snap ring is seated all the way and I cannot do that with the compressor installed. Then I can hook everything up and vacuum out the system. Let me know where I should go from there.
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Saturday, July 28th, 2012 AT 5:36 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
How much oil have you put in? I guess you are not understanding what I was asking. It does not matter if the rear is unhooked. My concern is that the hoses etc, are now hooked up like a none rear air AC system?If it is were good there.
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Saturday, July 28th, 2012 AT 6:02 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
I took it to the shop could not take it anymore. They replaced the control head for $270.00. I wished I listened to you. DOH
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Saturday, July 28th, 2012 AT 6:13 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.

Cheers
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Saturday, July 28th, 2012 AT 6:54 PM
Tiny
HAWTHORNE
  • MEMBER
  • 4 POSTS
  • 1997 CHEVROLET SUBURBAN
V8 four wheel drive automatic.

Front AC fine rear blows hot air only. Is there a valve for the rear?
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Monday, July 16th, 2018 AT 7:53 PM (Merged)
Tiny
DOBBER
  • MEMBER
  • 17 POSTS
There is a blend door for the rear evaporator core, check the actuator to see if it is moving the door.
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Monday, July 16th, 2018 AT 7:53 PM (Merged)
Tiny
EDIE MAC
  • MEMBER
  • 1 POST
  • 1997 CHEVROLET SUBURBAN
  • 20,000 MILES
I just had the front AC unit serviced and thought I was okay but the back is blowing hot air. Front is cool. 100+ temperatures in Georgia this week are challenging to front unit and it just will not cool the length of the bus.
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Monday, July 16th, 2018 AT 7:54 PM (Merged)
Tiny
DJCL
  • MECHANIC
  • 767 POSTS
There is a separate system for the rear. But it uses the same r134a charge.
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Monday, July 16th, 2018 AT 7:54 PM (Merged)

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