100 psi low pressure a.c. port?

BrianX128

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Turned my a.c. on in my truck today first hot day of the year and had a red tek 12a geyser.

A.c. worked perfectly for months last year. 35-40 psi and ice cold.

I shut it off and got gauge for low pressure port. Off the chart with engine off. Obviously. Turned a.c. on max and had 100+ psi on low port. Stood there for 5 minutes letting it blow out and went all the way to 20 and had to put some back in.

Now it seems totally fine.

What the hell just happened?

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chris142

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Thats your high pressure reliefe valve. For some reason you made over 500 psi on the high side. Bad fan clutch? Plugged orifice tube? Over charged?

And those reliefe valves are usually a 1 time deal. They dont usually seal back up.
 

junk

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If it worked before I'd wonder about plugged orifice tube. Not sure why it would have plugged just recently though. Was it cold outside? Any chance you have moisture in the a/c system and it froze up the orifice tube?

I've had my pressure relieve blow like that, but it was with a plugged radiator on super hot/ humid weather. So i wasn't getting much cooling air through the condenser.

Mine did seal back up sorta. i've got a slow leak now and wonder if its that pressure relief port.
 

BrianX128

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If it worked before I'd wonder about plugged orifice tube. Not sure why it would have plugged just recently though. Was it cold outside? Any chance you have moisture in the a/c system and it froze up the orifice tube?

I've had my pressure relieve blow like that, but it was with a plugged radiator on super hot/ humid weather. So i wasn't getting much cooling air through the condenser.

Mine did seal back up sorta. i've got a slow leak now and wonder if its that pressure relief port.

I'm starting to think your on to my issue though my a.c. knowledge is poor. When I got the truck it had 0 anything in it and I jumped the compressor and it worked. I read an article and watched a YouTube video of a guy fixing an empty ford a.c. system with 2 cans of ester oil and 3 cans of that red tek 12a stuff.

I bought the stuff did the same and my a.c. worked beautifully for 6 months until winter came and wasn't needed. During those 6 months if the a.c. was on for over an hour it would feel like it stopped blowing as much air.. but if I put it to vent for 5 or 10 minutes and turned it back it was normal again.

Well today when I was letting out all that pressure from the low pressure port after this happened, amongst the gas coming out for about three or four seconds some actual liquid goop came flying out and then back to gasses.

Could my orifice tube have been partially blocked and after sitting all winter everything settled there causing this mess today? It was the first time I had ran the a.c. and worked the truck hard. It happened as soon as I turned the a.c. on when I was almost home and the truck was hot.

What is strange is, after I emptied it down to 20psi low side with a.c. on, I filled it back to 35 and the a.c. is ice cold.

I just now drove the truck 45 minutes to my girlfriends moms house with the a.c. on max cool fan 3, and it was perfectly fine. And, the old "tired fan" effect I used to have of feeling like I lost air speed out of the vents is gone. It was still blowing just as much cold air at me after 45 minutes straight which didn't use to happen.
 

chris142

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The loss of air flow through the vents is likely a bad cycling switch. It's not letting the compressor cycle out and is allowing the evaporator to ice over. A new switch is $25 and takes 15 seconds to change. I don"t know what "Red tech" is. I assume some sort of illegal refrigerant?
 

BrianX128

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The switch that one would jump to force the compressor on? I'll have to order one then cause I don't think it does ever cycle once it's on it just seems like it's on.

Red tech is basically pretend r12 that you can put in old r12 systems and it's supposed to make old non converted 134a systems still work. Outside of this one hiccup which may be unrelated I've had it in the idi for over a year and it works fantastically. Really cold air and never leaked out.

http://www.redtek.com/win_12a_refintro.html

I have put it in 3 dead a.c. systems now with some ester oil and all 3 still work perfectly to this day. One being my old cavalier, and those three cans have been in it for 10 years without topping it off since I got the car junior year in high school and found the a.c. didn't work and had no psi at all.

It's far from the right way from doing things when leaks had caused the systems to empty out, but some ester oil to swell the seals and this stuff having bigger molecules to help against leaking out according to the company and its served me really well.

I've put a can of 134a in my 250 and watched as the pressure disappears as the 134a gets passed the o rings, and then put a can of this stuff in and watched as it never lost pressure. I've never had to top off any vehicle I've put it in. That's why this was so strange today when I had issues.
 
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chris142

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Ya the switch on the accimulator. I read up on the red tech stuff. Sounds great...unfortunatly its not a legal refrigerant according to our govt. But lets save that for another thread.

Btw I specialize in auto ac.
 

gnathv

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If you're not pulling the system into a vacuum you will have odd problems.
 

chris142

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With Some of the hydrocarbon refrigerants they say not to pull a vacuum,
 

79jasper

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Their instructions don't specifically say to have a vacuum. But does say "evacuate the system."

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Macrobb

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So... Yeah. The stuff is basically propane/LPG, more or less. EPA doesn't like it, but it works just fine in terms of making things cold on one side and hot on the other.

Propane(and things like it - butane, isobutane, a mix etc) is a liquid at a certain temperature and pressure. Add more temperature or less pressure and it turns into a gas. Cool it or compress it and it becomes a liquid again.
This is basically how an AC works, generally speaking.

The thing to note, though, is that once you hit the 'vapor pressure', the pressure won't keep increasing as you add refridgerant, because it will simply turn into liquid.
In your case, that's what happened - you ended up with a lot of liquid in the system.
My guess is that it settled in one spot over the winter, and when you turned it on, the compressor pumped a lot of liquid through the system all at once, and created a really high pressure which blew the relief valve.

I'd aim for a lower low-side PSI - 25-30 should do better, depending on temperature.

Also, as a general rule, you should try to evacuate the air out if you can, if only to prevent an explosive mixture of propane/hydrocarbons and air.
No, you probably won't have enough air to actually make it explode, but it's still a good idea. It'll probably make the system work better, too, as air won't compress to a liquid. And it's the gas->liquid "phase change" that moves a lot of energy in an AC system.

Also, you commented on the AC stopped blowing much air? That's because the AC evaporator froze up. Propane at those pressures in a R12 system will produce plenty cold temperatures, and it's more efficient at moving heat than the R12 that it replaced. This simply means that you'll end up freezing up more, unless you lower the low-side pressures.

You can also get one of those "therm-O-disk" 32F thermostat switches and just stick it there on the evaporator line, then wire it inline with the low-pressure switch next to it. Once it gets cold enough, the thermostat opens up, which stops the compressor and lets the system warm up again. You won't notice the difference inside the cab, as the condenser is still near freezing.
 

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