96 chevy Tahoe A/C clutch is not working correctly. (Strange problem)

[Sarcastic_cook]

Hi guys,

I am new to the forum and have a strange problem with this truck.

I am working on a 96 Chevy Tahoe 5.7L with front A/C only. my neighbor asked me to evac and charge the a/c system. When I was finished everything worked fine and blew cold. When i shut the driver side door the a/c clutch went off. I checked the fuses and relay. Those were ok, but when I got to the low pressure switch: it has power to the light green wire. The dark green wire has no ground connection or continuity to ground. Basically there is not a complete circuit. Jump did not work. I checked the wires with a meter; it was giving me some crazy reading including the correct voltage but only for a split second. Any suggestions would be extremely helpful?

 

[SunlitComet]

From the control head you go light green to low pressure switch to dark green to high pressure switch to dark green/white to a/c enable request at PCM.

If you jumped only the low pressure switch wires to no avail and it suddenly quit working then perhaps the system was 1. overcharged and cut off with door closing was coincidental or, 2. you just happen to knock loose a wire loose by closing the door. At any rate it sounds like the high pressure switch is the culprit. When operating properly the head unit sends a positive voltage to the pcm but it must run thru the low and high switches in that order first. Both should be on the compressor.

Also ensure you ground wires at the thermostat housing are intact.

 

[Sarcastic_cook]

Thanks for the info. I will look further into that. I used a scale to be sure the correct amount of refrigerant was added. This is actually the second one that I have seen with this problem. I did not know that the wires went through the high side switch too. If it is the high side switch is there a valve there to prevent refrigerant loss when it is replaced?

 

[SunlitComet]

I don't believe so. For safety reasons that would have to have a direct measurement of pressure. Only the low side has one my data shows.

 

[Sarcastic_cook]

96 chevy Tahoe A/C clutch is not working correctly. (Strange problem) Reply to Thread

If the problem is in the wiring where would be a good place to start or work from? Besides the thermostat housing as mentioned in your last post. I want to thank you again for your help.

 

[SunlitComet]

follow the wire trail as described above. the high switch is on the back of compressor. Do that thing you that you have done so well so far(jumpers). Not for to long just in case the system is actually over charged or you will blow the entire relief valve.

For reference:

in case you wondered what pressure would activate that switch.

The system is also equipped with a high pressure cut off switch. This switch is normally closed, and opens at 2827-3103 kPa (410-450 psi ) to interrupt the voltage to the compressor clutch coil. This will stop the compressor from cycling and prevent the pressure relief valve from discharging refrigerant and oil.

 

[Sarcastic_cook]

If it was overcharged and kicked off the compressor, wouldn't it kick back on once the pressures equalize or drop below the switch settings?

I am pretty sure you are correct about the high side switch being the problem. I thought both switches had a separate circuit. That was my assumption yesterday when I read the wiring diagram in the manual. I stopped after the low side switch because the diagram shows it going to the pcm (If I read it correctly) lol. I will go through the electrical very carefully and see what I can find.

If it is the high pressure switch; is there a way to change it without losing the refrigerant in the system? Or can I leave the jumper in for now. I also found a very small leak that we will be fixing soon.

Just to be clear on the switches. When you said there is also a high pressure cut off switch dose that mean there is a (low side switch) a (high side switch) and a (high pressure cut off switch)?

 

[SunlitComet]

you will have a low pressure switch also called cycling and a high side switch also called high pressure cutoff. They are wired in series with each other. My data shows only the low switch can be replaced without system discharging because it has a service valve. Not personally verified my self yet. I just need to replace the high side valve core myself on day and you usually don't need to to discharge for that. check and find anything else wrong and while discharged look for continuity at the high side switch contacts. if none replace if you do then suspect it may have over charged or a restriction in the orifice. Don't take a chance with jumpers on the high side.

 

[Sarcastic_cook]

Awesome! That makes more sense now.

The system is still charged and has dye in it to look for any other problems. If it’s the high side switch I will have to start all over again. I am not sure about the compressor either. The system look fairly new but it had a lot of dirt build up on the front of the clutch. I cleaned it off and hoped to verify with dye before I discharged the system. The leak I found was while using a sniffer on a steel line going to the evaporator from the accumulator. It has some tool damage so I checked and found a leak. No oil though.

I will go over the truck either this evening or tomorrow evening and let you know what I find.

You have been super helpful. Thank you.

 

[Sarcastic_cook]

Ok so it was not the high side switch either.

When you said that both switches where located on the on top of the compressor I thought that was just a general location for Chevy. In this truck the low side switch is on the accumulator and the high side is on the compressor.

So anyway here is what happened. I pulled the connector off the high side switch put a jumper in, and nothing. At that point I noticed a wire sleeve (the black stuff wires are put in to protect them, I can’t remember what it is called) was dangling freely in the engine compartment. I pulled it up and found another low side switch connector with a jumper that was old and corroded so i pulled it out and put in a paper clip. Problem solved. I assume that was for the original switch.

I have never seen anything like that so I tested to see if leaving a jumper would cause a problem. No matter what I did they both had to be connected in order to turn on the compressor. I cut the connector off by the compressor and spliced the wires together; taped it up and zip tied it out of the way. I did that figuring that the other one connected to the low side switch would protect the compressor if there is pressure loss.

Was that the correct thing to do given the situation?