Engine A/C help please

Wayne Waldrep

Before I post a pic, do you have one of yours?
Dirt-Old 20+Year Member
Apr 14, 2003
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Cuba, AL
Lets try something new. No overabundance of boring details... Sorta. Me and my good friend have both tried to get the proper low-pressure switch for my car. 88GT. He owned the Napa in my town since we were kids (his dad started it back then.)
Finally, after much grief, we found that this is where the leak was back then.... About 5 years ago.
I have a kit with every size green oring available. None fit correctly to me. The one that comes new with the low-pressure switch isn't even close. Here's what I think the problem is. The threads on the switch are plastic up in there. When i put the switch on the fitting it's very wobbly. I can't imagine that's correct. I finally got it to seal back then but I guess not completely. Very slight leak. It would push the green oring out of the bottom when twisting the switch on. It presses the Schrader valve as y'all know. There's a flat ledge up in there that the oring mashes against. Anyway....... Help!
Ask anything you want. I need resolution to this once and for all. Getting hot here and I will not ride without ac.

Thanks.
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Put some Teflon tape on the threads of the Schrader valve leaving the first couple threads bare. Some pressure switches have an o ring all the way inside where that flat piece pushes the valve. Haven't looked at a fox pressure switch in a long time.
 
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switch.JPG

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Here's a couple views. I've tried putting the oring up into the switch hole first and also on the schrader valve housing like the other pic. Apparently, I couldn't get either to work like they should or I wouldn't still have a leak after all this time and effort. Supposed to be a simple screw off then on fix.
I could try the teflon tape but I'm sure I did back then. Just can't remember doing it. I want to fix it right this time though, so still interested in someone telling me why the dang switch is so floppy. If this were a bolt, it would be like having one size too big/small depending on how you look at it. I can almost pull the switch off once the threads are engaged but not tight yet. That's how much it wobbles. Everything I find says those threads are 7/16-20. Can anyone tell me if all of these are the same threads? Thanks.
 
My switch is definitely not floppy. It's pretty tight actually. If your switch is moving around, it's going to leak as the seal makes and breaks depending on movement.

Have you tried another switch?


Also, try some of this stuff. It's an A/C sealant. Put it on the O-ring and contact surface of the flare. Will help seal.

Amazon product ASIN B008HOSQQQ
View: https://www.amazon.com/Refrigeration-Technologies-RT201B-Gasket-Sealant/dp/B008HOSQQQ/ref=sr_1_1?keywords=nylog%2Bblue&qid=1680026972&sr=8-1&th=1
 
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Thanks Mike. I guess I'll drive the car over to O'Reilly and grab a few to see which will fit correctly. Then i can fight with the oring after that. Weird to me is that all of those dryer fitting are 7/16-20. Seems like any of them would thread on snug huh?
 
Let me clarify something. Without the o-ring in it it's wobbly. I wanted to check it like that to see if the threads were engaging properly. Tell me if I'm wrong but shouldn't the threads still be snug even without the o-ring in there? Like I said above it feels like when you put a metric or standard bolt in the wrong hole. You can tell the threads are engaging but they're not the right size. So Mike, when you said that the switch on yours is really snug does that include without the o-ring being on the inside?
 
Don’t know really. Never took it off as it came oreinstalled on the accumulator. Don’t really want to take it off though.

I haven’t really changed this switch much, so not a lot of experience there.
 
Yeah don't remove it....lol. I'll report back after i try a new one...or two. Thanks.
One more question. Are all the Schrader valve cores the same?
 
Not all of them, but the vast majority of modern short style cores are these.

Riseuvo 100Pcs Schrader Tire Valve Core - American/US Valve Stems Core for Most Automotive, RV, ATV & Air Conditioning, Tire Remover Replacement https://a.co/d/2jJCxQM


This is what was in my ac system. If you ask for an ac valve core, that’s typically what you get.
 
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The one in your pic is a looks like a standard 1/4" flare fitting, they will all use the same Schrader core. You might try an encapsulated pressure switch for a standard HVAC application. Several vendors make them with various cut-in & cut-out ratings. The bodies are brass or steel, & usually use a copper sealing ring. Alot better than that B.S. plastic & o-ring. Supco part #'s SLP-2045 & SLP-1535 are an example.
 
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This is it, but I was only able to use it on the low side port. Not the high side. I did not try the port on the accumulator.

Price went up. A lot. Think I paid $45
Appion MGAVCT 1/4" MegaFlow Vacuum-Rated Valve Core Removal Tool https://a.co/d/fqsQ2pB

Confirm that the accumulator port fitting is the same size as the low pressure fitting. If it is, this will work.

I can also send you mine to use if you’ll cover shipping.

But this will allow you to swap cores on a fully pressurized system.
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I just watched this video......
View: https://www.youtube.com/watch?v=SIR1Ro13u1A


At the 45 second mark, he says "on a Ford, anything below 1994 model the AC compressor is supposed to stay on constantly if you have the AC or Defrost on. Anything 94 and up that switch is made to cycle the compressor off and on."

Umm.....I have never heard that once in my life. The switch even says the on and off pressure and it's adjustable. Or am I wrong? I just personally have never seen or heard of a foxbody AC compressor that doesn't cycle on an off. Will someone please clarify?
 
It depends.

The switch is designed to open at ~25psi and close once pressure creeps up to 45psi. WHen this occurs all depends on ambient conditions.

Assuming a properly charged system, on a 95 degree humid day, the system will likely stay engaged indefinitely. System pressures will run higher and the low side will likely never drop to a pressure low enough to open the low pressure switch.

On a cooler day, the system pressures will likely be much lower, and it's possible to occasionally hit that 25psi limit. This might be true if running the defrost on a humid 45 degree rainy day for example.

There are other factors as well. Airflow through the condensor will play a role in pressures.

When folks convert to R134a, you should really adjust the switch down to around 20-21psi. The R134a has a wider pressure differential across the orifice so it's much more likely that the lower side will approach pressures in the 20 psi range. Since a lot of folks don't adjust the switches (or just don't have the meants) it's possible to hit the low pressure cutoff a lot sooner than necessary. So you get a cycling system. It's going to be a lot more common on these r134a retrofits, especially if done on a leaking system without an adjusted pressure switch.


My new R12 system behaves as i describe above. Hot day, it runs pretty much constant and gives me 35-40 degree vent temps. On a cool day, it cycles
 
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