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High and low side don't equalize after shutdown Pages: 12

jga2z on Mon May 09, 2011 4:25 PM User is offline

Year: 2003
Make: Pontiac
Model: Montana
Engine Size: 3.4
Refrigerant Type: 134a
Ambient Temp: 85
Pressure Low: 45
Pressure High: 220
Country of Origin: United States

This van does have rear air/heat. To start with the vent temp is at best 52F. static pressure is 95psi. I am a bit stumped as I have not seen this symptom before. The high and low pressures take near 30-40min to equalize after shutdown. At 2000rpm high side climbs to 300psi +, low drops to 30. Higher RPM 3000 High side goes near 400. Both frt and rear lines feel same at TXV Hi warm, lo cold. Don't have actual temp readings.
Could 1 or both (front or rear) of the TXV's be bad? How could I tell which one it might be?

I have added a bit of 134a to get to these readings as the vent air was maybe 60F when readings were Hi 150, lo 30 @80F I didn't notice excessive high side readings at that time. I suppose I might have an overcharge at this time, but at no time did vent temps get below 50 during charging.

Edited: Mon May 09, 2011 at 4:39 PM by jga2z

Dougflas on Mon May 09, 2011 4:33 PM User is offline

If I were working on this vehicle, I'd recover the charge and place a percision charge in it and go from there.

GM Tech on Mon May 09, 2011 4:51 PM User is offline

You are dealing with "no-bleed" TXVs-- that is how they work-- as designed by manufacturer.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

jga2z on Mon May 09, 2011 6:03 PM User is offline

OK I guess that should explain the slow equalization. Maybe that would make for quicker cold vent air on restart of AC.
What about @3000rpm+ the high side going higher and higher up to 400+ with low side going down to 25-30?

Edited: Mon May 09, 2011 at 6:06 PM by jga2z

GM Tech on Mon May 09, 2011 6:06 PM User is offline

How are the cooling fans? Both running during all this?

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

jga2z on Mon May 09, 2011 6:08 PM User is offline

fans are running perfect. Going to high speed, on all the time. Coolant temp is a bit low ~180?

mk378 on Mon May 09, 2011 8:58 PM User is offline

Assuming the condenser is being adequately cooled (Is it free of dirt and leaves, etc?), other reasons for excessive high side are being overcharged with refrigerant or oil, or refrigerant contaminated with air.

jga2z on Mon May 09, 2011 9:31 PM User is offline

Condenser is very clean. I think excess oil might be present as I slowly bled off a bit of pressure thru the gauges and there was oil coming out of both and high and low side. A lot more from hi side.
Air in the system is not very likely but not impossible.
I hate to think I might have to flush system and start with fresh known oil fill.

HECAT on Tue May 10, 2011 7:49 AM User is offline

Quote
Originally posted by: jga2z
I hate to think I might have to flush system and start with fresh known oil fill.

If oil overfill is indeed the culprit; how else can it be resolved?

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

NickD on Tue May 10, 2011 8:56 AM User is offline

PAG really can sludge up of exposed to moisture causing additional problems like with your TXV. On a new vehicle, OE's draw a full vacuum first, then inject the PAG, so its never exposed to air.

Can you add anything to how you did it differently? Was your system exposed to air?

If there is any kind of trend with MVAC over the last 50 years, they are a hell of a lot more difficult to work on today with a lot more to do. Really changed in the early 90's when the EPA got involved. Would really be nice if they published any environmental improvements they have made. But I feel they have made this industry a lot worse.

As Chick says, where is Chick by they way? Just my opinion.

Edited: Tue May 10, 2011 at 9:07 AM by NickD

jga2z on Tue May 10, 2011 1:39 PM User is offline

I just got this van, dealer trade in/auction/dealer(who doesn't fix much)/me. As far as I know nobody has messed with it. It was just low on charge 30/120 with 60F vent [email protected] amb.
I may have forgotten to purge the high side gauge line (which have valves on port ends) but since it is not going in I don't think that would matter. I did of course purge tank line when I started charging.

I think I'll start with an empty system, leaving whatever oil is in the system, vac with 5cfm pump for an hour or so and recharge and see what I get.
Any comments on how to decide if Front or Rear TVX might be bad for this or future reference.

Edited: Tue May 10, 2011 at 1:42 PM by jga2z

bohica2xo on Tue May 10, 2011 2:28 PM User is offline

Quote
Originally posted by: jga2z
Condenser is very clean. I think excess oil might be present as I slowly bled off a bit of pressure thru the gauges and there was oil coming out of both and high and low side. A lot more from hi side.

Air in the system is not very likely but not impossible.

I hate to think I might have to flush system and start with fresh known oil fill.


You have a mess. Add a little, bleed a little... No idea how much refrigerant or oil is in the system. High pressures. Poor cooling. A first class pig sty.

Only one choice. Tear it down, flush to bare metal & start over. The vehicle is 8 years old, and the dryer is ready for replacement if it is original. Time to go through the system completely, while you still have a compressor in good enough shape to make 400 psi. Keep jacking around bleeding & adding, running outrageous pressures - and it will still need the same labor but many more expensive parts.

.


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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

jga2z on Tue May 10, 2011 3:46 PM User is offline

Indeed a mess. The car this van is replacing is even more an AC mess.

Should I change both the frt and Rr TXV's and the dryer? After flushing ?
I've never done a flush. Will have to read up on it.

NickD on Wed May 11, 2011 11:33 AM User is offline

Entire automotive industry is a mess, how can they offer five years of payments with only a three year warranty? And that doesn't cover the brakes, tires, exhaust, AC (well maybe for one short season), nor those tiny paint chips. Friend just purchased a new SUV with those high monthly payments, looked up the new tire replacement, over $1,500.00. Got a tiny stone chip on his hood, his dealer wants $460.00 to repaint the hood.

Neighbor went to our Ford dealer to trade off his 3 year old pickup, was only offered less than half the Kelly trade-in value that is only a fraction of the retail value. And rare to find any used vehicle at a dealer as even as low as retail value. And none of these people I know can't even change a spark plug let alone do any serious work. Average shops rates in our town is a hundred bucks an hour.

So I guess if you want a decent AC system, you better work at it. Hecat has plenty on this board as to how to flush a system. Still say you are darn lucky your system didn't blow up in your face. One thing to be thankful for.

bohica2xo on Wed May 11, 2011 3:56 PM User is offline

JGA

The decision on the TXV's comes when you inspect them. If the front unit is easy to get to, and it is clean inside with no corrosion - I would probably re-use it. if the rear TXV is a real bear to get at? replace it.

The condensor in that vehicle is also the primary filter, and is very difficult to flush well. As it is a 150 dollar part I would replace it if there is any reason to flush it.

The evaporators can be cleared of oils by flushing, and are usually not too bad. You will need plenty of compressed air.

All of the hard lines flush well. Any flexible lines that have no "cans" or mufflers incorporated can be flushed as well.

Since this is a used car it may have any number of products in the system right now. This includes every "magic in a can" product at the local auto parts store. The good news is that most of the time the "magic" is a mix of solvents & oils that were intended to swell the seals to slow down a leak - and replace lost lubricant from the leak. There is one sealer out there that can be a real problem - it hardens when you open the system. Most of the time I find the cheap oil & solvent mix has been added.

If a component was replaced by a beginner, extra oil may have been added at that time too. Extra oil, with no evacuation before recharging will produce the symptoms you describe.

The short answer is you simply don't know what the past owner did without opening the system & starting from square one. The compressor in that system is a 400+ dollar item. Break things down, clean & inspect the TXV's. Perhaps a new condensor. 200 to 300 bucks in parts. As new performance when you are done.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

jga2z on Fri June 03, 2011 10:31 PM User is offline

OK I'm over my reluctance to flush the system and spend the money if I have to. With temps now in the 90's I HAVE TO fix this AC system. 55deg air ain't gonna cut it.
current update...@90deg- lo 45psi, hi 220psi at idle 55deg vent. at 1700 rpm lo35 hi 300+. Doesn't this system have a high pressure cutoff switch?

Quote
Originally posted by: bohica2xo
JGA



The decision on the TXV's comes when you inspect them. If the front unit is easy to get to, and it is clean inside with no corrosion - I would probably re-use it. if the rear TXV is a real bear to get at? replace it.

Both are not terribly hard to get to. If both F and R vent temps are the same would that indicate TXV's are both functioning the same?
If I had just 1 of the 2 "bad" wouldn't the vent temps be different?

Quote

The condenser in that vehicle is also the primary filter, and is very difficult to flush well. As it is a 150 dollar part I would replace it if there is any reason to flush it.

It looks like the condenser is a separate component. By filter do you mean the dryer? I don't see another piece. Shouldn't I be able to flush the condenser and replace the dryer?
I can get a new cond for $85 and receiver/dryer for $14. TXV's are
To get back to the main symptom of excessive Hi side pressure. To resolve it by starting from scratch: flushing, part replacment etc. Do I need to remove and drain compressor oil? Where do I put the correct amount of replacement oil?









jga2z on Sat June 04, 2011 12:07 AM User is offline

As I just drove tonight @80deg outside the front vent is 45, and rear is 55. Never really compared the 2 this closely before.
Could I have just a bad rear TXV and it cause the excessive high side pressure?

bohica2xo on Sat June 04, 2011 2:03 AM User is offline

Your condensor IS the primary filter. With tiny passageways, and multiple paths. Once a passageway plugs up, the cooling load shifts to others... plug enough & you can't get rid of the heat.

Your problem may be just way too much oil, but to find out you would need a high quality flushing tool to clear the condensor. It is usually more cost effective to replace the condensor - because you will already have it out of the vehicle.

Since the TXV's are easy to get at, wait to inspect them before replacing them.

You flush the compressor with fresh oil of the same type you intend to use in the system. Once you are ready to close the system up, you put the oil charge into the system. Usually the compressor will take a lot of it, then put the rest wherever it is easy - usually poured into the receiver or accumulator. Once the system starts, the oil moves around quickly.

Once the system is closed up, you can pull a vacuum. If it holds vacuum, you can charge it after you pull it down to less than 1000 microns & hold it there for at least a half hour.

Be sure to charge into vacuum with the compressor stopped. Try to get as much refrigerant as you can in before you start the compressor. Do NOT jumper any switches to charge the system.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

tomw on Sat June 04, 2011 11:46 AM User is offlineView users profile

For what it's worth, the temperatures out of the front and rear vents will differ because of the varying airflow over the evaporator coils. They both draw ~ equal temperature air from inside the vehicle, but flow different CFM through the fins. Whichever flows more air per volume of refrigerant will be warmer. If the TXV were stopped up, you'd get no cooling along with high head pressure.
The guys have told you that you are truly dealing with a pig-in-a-poke when you get a system that has no pedigree. They could have used snake-oil for lube[joke...] for all you know.
I didn't see it mentioned, but PAG will start to absorb moisture the minute you open the container, if not before, so if you flush the compressor with PAG, you want to try to keep the inlet & outlet covered as much as possible. I'd use ester, if it were my choice.
tom

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simplificate and add lightness

jga2z on Sat June 04, 2011 2:58 PM User is offline

Just another thought. If misting water on the condenser drastically lowers high side pressures, given my other signs does it mean the condenser might be plugged up and not other parts like TXV's? As I stated the cooling fans are working fine and no obvious external obstructions of condenser. I know in general the water trick is going to lower hi side pressures.
Sorry about dancing around the issue of flushing, but I'm looking for signs to use for future reference in troubleshooting other vehicles.

jga2z on Sun June 12, 2011 1:04 PM User is offline

I'm still trying to decide if I need to change the TXV's, front or rear.
I don't think I really have an issue with them considering general performance of system, and an off car inspection/test of them seems dubious as to whether or not it could be determined they are bad.
Yesterday @70 deg outside it was blowing 40 deg vent air in front, and 45 rear while driving. When it's 90+deg outside it would only blow ~60deg vent air. This fact makes me think there is an issue with adequate cooling of the condenser (both fans are working fine as far as I can tell), or hopefully it (or the dryer) was clogged internally and I'm not wasting my time changing it.
While I was changing the condenser I discovered it had already been changed along with the dryer. It wasn't done anytime lately from the looks of things, but makes me wonder.

It turns out the rear TXV is NOT easy to get to, so I'm really trying to avoid that.

jga2z on Sun July 03, 2011 12:38 AM User is offline

Well since I hate leaving an open question unanswered here's the end result.
I ended up flushing system except for the rear evap which is a serious pain to get to the TXV. Checked the front TXV (perfect) put in a new condenser w/dryer which looked like they both had already been replaced at some time in the past (I suspect this was my major problem), added 8 oz of PAG46. Evacuated, Recharged, using gauges only as I have no scales to measure my 30# bottle by weight.
Everything worked fine after all that. Blows in the high 30's @90deg
The wife drove from MO to CA with no probs, stayed cool in the 100deg+ SW.
Thanks for all the help everybody.

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