High pressure needle

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High pressure needle

Postby johnfin » Thu Apr 07, 2016 1:23 am

2004 GM 134a- Static pressure low 80 - high 90 Dynamic pressure=low 25 high=150~200 and the needle goes back and forth slowly every 4 seconds. Does not cool. Compressor runs does not cycle. Used UV trace dye and dont see anything. Anyone have documentation that shows what could be causing this?
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Re: High pressure needle

Postby Tom Greenleaf » Fri Apr 08, 2016 12:38 pm

Welcome: Please always post year, make, model, engine, miles and other pertinent info like recent repair if applicable.
Also ambient temps as coming in thru grille while running and checking pressures helps.

12ish year old anything first reason for lack of performance is a leak and the loss of refrigerant. Finding them will be more than just dye but any which way you can. It has pressures that are doing something suggests system at large is working but pressure don't tell if charge amount is correct. You can only know that by charging the listed capacity underhood some place should be a sticker and charge properly from a well held vacuum then can diagnose a lot better WHY it isn't performing or that it does then for how long and find that leak,

T
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Re: High pressure needle

Postby johnfin » Sat Apr 09, 2016 2:30 am

Tom, good thing you are not a doctor. Your statement about age and leaks is like saying 50 year old men die most of the time from heart attacks. 80-90 static psi hard to believe there is a leak. Also dynamic pressures high. Not symtoms of low coolant. Show me a link where it shows 150-200 high side needle moving up and down being the sign of low freon.
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Re: High pressure needle

Postby Tom Greenleaf » Mon Apr 11, 2016 3:07 pm

Sorry for the delay in approving post I try to be here every day if only for that.
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Yes - there's a prescribed "acceptable" leak rate which is years is the aim. MVAC by nature in moving, hot, cold, vibrating and a shaft to seal a gas under high pressure and super low temps when you aren't looking or using it.

The #1 thing to verify exact charge is in the system is to fill from empty/vacuum. The pressures give good clues for problems but never pin that it's precisely charged.

Now with that unless messed with it isn't gaining more you can only guess there's less than when last perfect. With that oil is slower to move and so goes the game. I find bouncing needles for pressures a result of slight debris most likely and no good explanation of when just a vac+charge frequently solves that? Really - it just behaves many times and IDK exactly what changed. Perhaps in state of vacuum debris moved out of harm's way?

I also strongly favor virgin new refrigerant vs sometimes unknown stuff you buy as all cleaned up and just as good but really doubt it sometimes.

The suggestion is just step one before tearing all over a system looking for things that are NOT wrong yet,

T
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Re: High pressure needle

Postby johnfin » Thu Apr 14, 2016 3:45 am

My official guess is the h-valve is stuck and the compressor is internally cycling. This explains the needle movement.
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Re: High pressure needle

Postby Tom Greenleaf » Thu Apr 14, 2016 4:40 am

At least your back - site undergoes constant spamming and hoped you didn't get lost in the clean up on isle 7 if you will.

What is this vehicle? 2004 GM sold a lot of different stuff!

"H" valves were a Chrysler thing but there's no telling which system concept you are working with unless you say or tell what exact vehicle and it can be looked up.

CCOT or Expansion Valve set up at least?

Again - pressures are a diagnostic tool but not good info on charge amounts at all really just show health of system is within perimeters of some norm expected.

Bouncing needles is one observation. What were all the condition when this was noted matters just as much.

Seriously - Anyone:

Please list out year, make, model, engine, compressor type if known, pressures, ambient temps, output temps, RPMs when taken and anything pertinent you can think of like recent work on it.

Also keep in mind every time you hook up and disconnect gauges you are losing a spit of refrigerant and it adds up to actually being low over just that not unlike continually checking tire pressure on a small capacity tire.

Everything matters and working on A/C is NOT a DIY friendly sport with high chances of messing things up,

Tom
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Re: High pressure needle

Postby Nacho » Tue Apr 19, 2016 5:14 pm

Please provide exact vehicle info. In 2004 there were dozens on "GM R134a" vehicles. If you want precise advise, give precise info.
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