a/c low side port at 120 psi

maverick

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#1
well my a/c worked when i got my 94 astro awd vortec with rear ac a fewe years ago. while working on it i accidentally cracked the nut on an ac line and closed it back quickly. it was in the winter so i'm not positive if that's when the a/c stopped working but i imagine it was. i got a recharge kit and the low pressure port reads 120psi and it blows warm air... my a/c classes don't start for a few weeks so i'm not well versed on ac. wha would a high pressure on the low side indicate? and how do i go about fixing it?
 
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#3
If the low side does not change when the compressor comes on then the compressor is no good. If the low side is 120 and the compressor is not coming on it can be a number of things like a bad sensor on the low side or to big of an air gap at the clutch and coil assy. Need more info. Also what is the high side pressure at? Post back Greasemonkey :)
 

maverick

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#4
well i don't know what the high side is because the recharge kit only comes witha low side adapter. but... i believe the compressor is not coming on. there is no voltage at the compressor. again' my ac classes don't start until tomorow so i'm kind of in the dark' but i understand there is a switch on the accumulator which doesn't let the condensor run with really low pressure. i jumped the switch to see if it made a difference but still no voltage. i checked the fuses and they were fine. anything else i should look for? or is it most likely a wiring problem i should search for?
 

TRB

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#5
When adding refrigerant do not even mess with an a/c system unless you have a full set of a/c gauges! With 120PSi if that is correct should be enough PSI to engage the clutch hub. If you have proper test equipment trace back to you dead stop. May need an Ohmmeter to check the pressure switches.
 

maverick

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#6
well i'm fine with electricity i just am new to ac. so the low pressure shut off switch i didn't know about before today and for all i know there are more cut off switches i'm not aware of. so where should i start with diagnosing no voltage at the compressor?
 

Gus

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#7
This looks like a cluster ---- from the get go.....

If the engine is cold and the temp is aound 70F, this thing is way over filled, though how that could happen if it never ran is a mystery....
 
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#8
These recharge kits should be outlawed and many do not provide pure R-134a, but seem to have a bug about adding sealers that can cause more damage than good. Precise operating pressures are imperative for proper AC operation and you don't get that with a low side gauge I wouldn't even trust to measure my tire pressures with. Another factor in particular with a 1994 GM truck, your system could still be R-12 as really a mix up in these years. And the chemistry of toping off an R-12 system with R-134a results in extremely high pressures much greater than R-12 or even R-134a is capable of. If you don't have clutch or other electrical problems, by adding R-134a to an R-12 system, it can blow up in your face.

What I hate about these kits the most, they assume and try to convince you that your only problem is that your system is low on charge. And you already told us you do not know the difference between static and operating pressure. Don't you think you should learn about AC systems first before even playing with one?

GM has more AC systems than you can shake a stick at, best to get an alldata to learn what you have. Most basic is 12V from the climate control through the cycling switch, through a high pressure cut-off switch, to the clutch. With the cycling switch switching the full inductive load of the clutch coil, they don't last very long. Other extreme is a microcontroller based system with sensors all over the place. Another common characteristic is that crazy interference fit clutch hub that can either creep in or out depending on it's mood, so you either end up with drag or a clutch that won't engage at all due to excessive gap.

Ha, but none of these are problems, right? Has to be that your charge is low.
 

maverick

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#9
you must not have read the whole post because we've established already that the problem is no voltage at the compressor. my system is 134a. not r12. i know the difference between static and operating pressures' i was simply asking if this high was normal. accrding to my ac instructor the pressure is fine. and yes i have mitchell and alldata. i will test for voltage at the switch tonight. any constructive advice?
 

maverick

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#10
well i found the cause of the no voltage. when i was checking the switch for voltage i found the harness came unplugged! plugged it in and the compressor came alive. the pressure normalized to about 30psi but it's not as cold as i'd like it to be. i'll add a little freon and hopefully it should clear it up. thanks for the input.
 
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#11
Guess I never thought about suggesting a loose harness connector, perhaps because I am very good at snapping the two together with one hand, either the left or the right. But takes me four hands to pull them apart, how did that connector come loose?

Regarding 1994 GM trucks that bit on the R-12/R-134a was strictly as a precautionary measure, while all vehicles produced in 1994 were to be equipped with R-134a and even some in 1993, GM managed somehow to squeeze some R-12 stuff through.

So what does your instructor think about your recharge kit? Even hate to suggest the proper means to top off a system using gauges, but will if you ask. But using a low side gauge only is not the correct way.
 

maverick

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#12
well i brought my van in to lab to diagnose a heating concern and some other students checked the switches so i assume it was then. it was in the winter though so i didn't notice. and i didn't ask about the kit... but i do know they generally frown upon them because of the added sealers. but i'm not too concerned. i only added a few ounces. but it's nice to have air now that it's 90 degrees out. and with 9 large windows' that van is like a sauna! thanks again for all the input
 

brcidd

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#13
If you want to speak intelligently about your A?C system (especially in class with an instructor) you had better not use the term "freon" - Freon is a trade name that Dupont used for their R-12 -- if you want to speak trade names then you should say I want to add "Suva" to my R-134a system-- and I wan to add "freon" to my R-12 system-- If you just want to speak in generics-- you say I want to add "refrigerant" to my system-- "Freon" implies you are putting R-12 into an R-134a system....

One of my pet peeves is when folks refer to R-134a as "freon"

more of the same-- a "kleenex" instead of a tissue
or a "Bandaid" instead of an adhesive bandage
or "Loctite" istead of thread locker
or a "Xerox" instead of a copy
 

wap

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#14
brcidd is right. but we know what you mean newbie. he's just bustin' your chops a little. here are some other 'brand names' that are commonly used to refer to common items:

kool-aid - instead of artificially flavored and colored sugar water
champangne - instead of sparkling double-fermented non-French wine
clorox - instead of chlorohydroxide solution
brcidd - instead of 'tightass enunciator'

keep tryin' kidd...don't be discouraged....lol....wap :ROFL