AC Not Cold Compressor Cycling on/off in my 1997 Chevy Tahoe V8 5.7L - can I test a high pressure switch?

[1997TahoeFix]

My 1997 Chevy Tahoe V8 5.7L air conditioning system blows air but it's not cold air. So last year I stupidly bought one of those AC pro recharge canisters from Walmart and gave it some freon. It seems to fix the problem and it blew cold.

Now a year later it's not blowing cold again. It's not cold at idle and it's also not cold at highway speed. It always just seems to blow room temperature air. I hooked up the AC pro canister again and it says the pressure is too high on the low side, it's in the red!

I don't have one of those high and low pressure testing valves but I can get one. I have no idea what the high pressure reading is. In the meantime, can I relieve the pressure somehow?

The fan works and blows hard. When I turn on the A/C by pressing the A/C button, the engine continually revs and the RPM jumps up then back down. In this video, you can see it . Is my compressor cycling on and off? These symptoms (when I search on this forum and elsewhere) suggest it could be a bad high pressure switch, which is protecting the system by shutting off. But then it tries to turn it on again immediately and shuts off. I'm not sure what's happening. Please watch this short video I filmed:

I have a few questions:

How can I get the system to the correct pressure?

I've heard some people trying to bypass the high pressure switch with a paperclip very quickly to see if that's the problem. But since the low pressure reads so high I don't want to do that obviously.


And lastly, what is this switch that looks slightly melted or burned? It has always been like this (even when I had the AC blowing cold) and I don't know what it does. I tied that little wire around it a long time ago to protect it from touching the engine bay when I noticed it was burned/melted.



Also if anyone can generally educate me where the high pressure switch is low pressure switches, some general labeling would help. Actually any and all help is appreciated. You guys are the best! Thank you.

 

[1997TahoeFix]

I'm an idiot, I just realized the AC Pro cannister's gauge always reads in the red when the compressor is off. I connected it, turned the AC on full blast and read the gauge.

It says it's empty, then slowly builds until it hits the red which is when the compressor shuts off:

What does this mean? Is it just low?

I can't seem to add any with the system cycling on and off. I shake the can, rotate it, the can starts to get cold and wet like it's dispensing but I can't get the gauge to ever rise above 10 or 20. Should I do it longer? I don't know when to squeeze the trigger. Do I need a new can? It really, really does not feel empty. I'm confused and annoyed.

 

[randeez]

yea sounds low.... i was reading thru the first post and was going to mention if its in the red the compressor probably wasnt running.

its only going to pull from the can when the compressor is on (suction on low side hose) otherwise the pressure in the system is too high for the can to "push" refrigerant in.

you can try to turn ac on high/recirc and just hold the trigger on the can wide open to see if it will get enough in to constantly run instead of cycle. you only need to worry about the pressure gauge when the compressor is on, dont worry about it going red when its off. low pressure switch needs around 25psi to keep compressor running iirc. you can usually jump out the compressor clutch by applying 12v to one of the wires pretty easily

for reference when the compressor is off and refrigerant stabilizes itll be around 80psi (this is why gauge shows red)

 

[east302]

In your last photo, that wire (blue connector) goes down to the sending unit for the cluster temperature gauge.

 

[1997TahoeFix]

Okay that's good news. Tomorrow I will try to get it to take the refrigerant. It's very difficult because it seems like I only have a brief window before it cycles again. I'm holding the trigger down on the A/C Pro and shaking it between the 12 o clock and 3 o clock position like the instructions say.

What if I turn the A/C Pro cannister upside down without shaking it in order to get pure liquid refrigerant to go in? (Just to get it up to the necessary amount where it stops cycling) will that help?

 

[randeez]

I would try and jump out the compressor clutch first to fill it. The compressor is supposed to suck in only vapor, if it sucks in liquid it could damage it. Possible it flashes immediately to vapor and causes no harm but I would avoid the possibility of causing yourself more problems since it looks like the low side port is right at the compressor

 

[1997TahoeFix]

To "jump out the compressor clutch," do you mean force it on by bypassing the cutoff switch?

Like with a small wire or paper clip? And where? I think some of the switches have three holes/prongs/connections inside. Anyone that could provide a visual guide of how to do that would be great. It's confusing because there's multiple switches. There's the high side, low side. Which one is actually causing it to cut off when there's no refrigerant?

I'd like to try a little longer getting refrigerant in without doing that. It makes me nervous to bypass a safety feature, especially one related to pressure. If there's a major leak or no refrigerant at all, I could definitely cause damage. There's obviously a good reason it's shutting itself off.