Questions regarding my AC and the low pressure switch

Chowder Head · Apr 26, 2010

Hey guys, little background. In the past, my car's ac was warm and that kinda went away after I added about two cans of refrigerant last year. I say kinda because the air was tolerable in warm weather but I still felt pretty miserable during the summer heat.

Well recently my AC's blowing warm air again and I want to get to the bottom of this. I've done some searching and it appears that the a/c low pressure switch can be jumped to detect problems but I have some questions.

1. How exactly do I jump the switch? Just stick a paper clip in between the two prongs? And what are the signs that this switch is bad? If the compressor kicks on once I turn on the AC? Problem is though my compressor already turns on (well it cycles on and off, which could be refrigerant related) so how would I identify the switch is bad and not that the compressor is simple cycling on again? If it continues cycling non stop or something?

2. I have a 95 GT. Will a low pressure switch out of a 94 V6 work or are they not compatible?

3. It may come down to this regardless but if I have to add some more refrigerant, at what psi (low side) do our cars like to sit at? My gauge has a green "safe" zone but I'd like to see if there's a specific number for our cars.

4. Lastly, regarding refrigerant, is it supposed to add slow? I distinctly remember adding some last time and it seriously took forever. Could this be because of the low pressure switch or is this normal? Maybe I should add the refrigerant with the switch jumped this time?

I think that's it. Hopefully I can finally get my AC blowing cold in time for the ridiculous FL heat.

Any replies would be greatly appreciated, thanks in advance!

Hef5.0weisen · Apr 26, 2010

Don't have all your answers but I'll give it a try...

paperclip will work fine, but to be clear, use it to contact the pins on the the plug/wiring harness, not the switch itself (wouldn't mention it if I hadn't seen it before)

the cycling of the compressor says it working, but may sense low pressure intermittently.....

I'd be looking for a leak somewhere....I think the o-rings are pretty popular for being worn out, In fact, I had a similar problem to you, found bad o-rings, right around the line by the pressure switch....cheap to replace, available at the the reular parts stores...

if you take one of the lines off you'll see them right there, easy to determine of they're shot. (you'll need those special tools, again cheap, available at the regular parts stores, same as fuel line disconnect tools)...you may want to hug a tree afterwards....
good luck

RatStang · Apr 26, 2010

You can purchase a can of dye for the air con system at your favorite parts store. All you need then, is a black light and semi-dark workspace to shine the light around and check for leaks.

Something along these lines might be ideal for your circumstance:

Amazon.com: R-134a Refrigerant with Leak Sealer/UV Dye & Trigger: Automotive

Chowder Head · May 2, 2010

Hey guys, got an update because I'm stuck.

Well I added two cans of the refrigerant with the dye and noticed some dye present on the low side ac line. Here's a pic for reference. FWIW, this is NOT my car. I just snagged it from google.

See the low side connection immediately above the compressor? Well the dye is there, specifically on the side of the connection that right on top of the belt.

What should I do? Do I have to replace the entire line now? If I do, do I have to remove all the refrigerant first? I'd hate to throw away money like that, not to mention the install and cost of the new line itself. This might sound blasphemous but can I add some JB Weld on the connection part where the dye showed up? Or will that not work? Has anybody used JB Weld on an ac line before?

I have a can of refrigerant I bought and haven't used but I don't know what I should do. I plan on getting a new ac cycle switch tomorrow but I don't know what to do after that. What should I do? Add the last can to see if it changes anything and look for other places where there might be dye? I didn't think of looking underneath the car while dye checking it and I could try that sometime.

So what should be my next move? And FWIW, after the two cans the compressor was still not cycling at all. It still did it when I jumped the low pressure switch but that's the only time.

Oh, and does anyone have pictures of the most common places for ac leaks in our cars? I know Hef mentioned the O-rings in the line, but I'm still not sure if I have to remove all the refrigerant. I'm guessing I would have to but I'm still curious to see if it's absolutely required or not.

Any reply would be appreciated, thanks! It's gotten hot here in a hurry and I need to get this fixed lol.

revhead347 · May 3, 2010

Just to clear up how the system works. The switch on top of the drier/accumulator is actually called the cycle switch. It is both a high and low pressure switch. It kicks the compressor off when the pressure gets too low, and when it gets too high. That's why your compressor keeps cycling at idle, you don't have enough gas in the system. If you have dye or oil coming out somewhere, that's where the leak is. Don't bother pulling one off a V6 and putting it on your car, that switch is pretty damn cheap, and there is no reason not to buy new.

Now here's a little reality. Anytime you open the system up, and drain out the gas completely, you have to have it evacuated completely, add oil, and have it refilled. A shop charges about $80 to do this. That high pressure line is about $80, and anytime you open the system, you have to replace the drier/accumulator, which is another $45 or so. R134A is about $6-$8/can. Always buy the store brand. It's all made by Dupont under patent anyway, so don't bother paying for name brand stuff. If you continue to leak out only 2 cans/yr, that means you can go 12 years just refilling it for the cost of repairing it. And that's if you do most of the work yourself. So if you are not analy retentive about everything in your car working perfectly, I'd just keep putting 2 cans/yr in the system.

Kurt

Hef5.0weisen · May 3, 2010

by no means disagreeing with what Kurt said...

However, I replaced one of my lines, and had a couple others disconnected/opened up hunting for bad o-rings....never did any of that evacuate/replace oil/replace drier stuff.....I just put it back together added a few cans of the cold stuff till the pressure was good.....been working fine for 5 yrs now......not saying it is the proper way, but my car, my dime...and it blows cold air

agree with not being anal about it....

revhead347 · May 4, 2010

It will work without evacuating it, but the air will corrode your system over time. And it wont' be as cold.

Kurt

Questions regarding my AC and the low pressure switch

Chowder Head

Member

Hef5.0weisen

RatStang

New Member

Chowder Head

Member

revhead347

Apparently my ex-husband made that mistake.

Hef5.0weisen

revhead347

Apparently my ex-husband made that mistake.

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Questions regarding my AC and the low pressure switch

Chowder Head

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Apparently my ex-husband made that mistake.

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revhead347

Apparently my ex-husband made that mistake.

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