hair-pulling a/c problem

[sgtHVAC]

I've been working on and old Army unit which runs on r-22 with 9000 btu/h which I cannot figure out. Both the high side and low side pressures are slightly low (charge is correct, though) but the unit isn't pumping any heat whatsoever. Both the evap and cond coils are room temperature when the compressor is running and the only tempurature change is located at the quench valve which is icing up.

The sight glass doesn't show bubbles and was colored yellow indicating excessive moisture. I changed the filter-drier out and dried it out five times with nitrogen and then put in fresh refrigerant but the unit still isn't pumping heat.

What's wrong???

[dandyme]

[QUOTE

The sight glass doesn't show bubbles and was colored yellow indicating excessive moisture. I changed the filter-drier out and dried it out five times with nitrogen and then put in fresh refrigerant but the unit still isn't pumping heat.






What's wrong???[/QUOTE]


is that all you did?

[maxster]

what's going on with the compressor...if you can grab the discharge it is short of gas and or the valves are shot...hows the amps vs the tagged rating?not throwing heat what happens in the cooling mode and whats yor OA temps.

[Texas-Tech]

is it a recip , i'm sure it is if its older. Maybe compressor valves are worn out?

[Texas-Tech]

forgot to ask, where are you? Whats the ambient temp?:D

[weber]

Well, If you were a pro member you could get a lot more help in the pro section.

I would start by taking some accurate measurments, to see whats going on.

You said you purged with nitro, what about a vacuum pump? If so how low did you go?

[ckone180]

Definately smells of a worn out compressor. Not pumping enough would cause the low pressures. The sight glass is also not a tell-al, though it may help in certain situations. If the unit had a rated charge and that is what you put in there I believe the compressor the culprit. However, if you have low ambient temperature, charging by the sight glass could be tricky for a novice (not saying you are one.) Good luck.

[refer guy]

I've been working on and old Army unit which runs on r-22 with 9000 btu/h which I cannot figure out. Both the high side and low side pressures are slightly low (charge is correct, though) but the unit isn't pumping any heat whatsoever. Both the evap and cond coils are room temperature when the compressor is running and the only tempurature change is located at the quench valve which is icing up.

The sight glass doesn't show bubbles and was colored yellow indicating excessive moisture. I changed the filter-drier out and dried it out five times with nitrogen and then put in fresh refrigerant but the unit still isn't pumping heat.

What's wrong???

This guy sounds like a millitary DIY:D

[markwolf]

First take an amp draw.If the unit you are working on has a R.F. limiting wire harness you will need to track down the harness & take the reading at the contactor.
Moisture in the system with a frozen txv or worn valves would both be a problem for support echelon group.
Fill out your paper work & turn it in to your support group.

[PaysonHVAC]

No one is asking what the actual pressures were???

But I agree, that it sounds like low on gas or low compression.

But he said "quench valve" which makes me think metering device. Maybe it's a restriction, a massive one so it ices there but not picking up much BTU's to feel any heat/cool at either coil...??? :confused:

[usaf hvac retired]

What kind of "old Army unit" is it?... The old R22 package units that I remember were called "Dash 39's"...and they had straight electric heat strips....The newer units were heat pumps, but they used R134A.
The quench valve was sort of a diverting TXV that sent some refrigerant around the evap and straight back to the compressor to cool it in the high ambient desert conditions.

[absolute air]

How clean is you indoor coil ? or most likely bad valves.

[Shophound]

The quench valve was sort of a diverting TXV that sent some refrigerant around the evap and straight back to the compressor to cool it in the high ambient desert conditions.

Does this "quench valve" have a solenoid that isolates it from the system when there are not high ambient desert conditions? Since he's seeing icing at the quench valve, it may be stuck partially open and partly diverting refrigerant away from the evaporator, hence he thinks the system "isn't moving any heat". It would be moving heat in such a scenario, just not where he wants it to occur.

[sgtHVAC]

I checked and yes, there is a solenoid located on the quench valve line. Would you know how I can check to see if a quench valve is locked? I know how to check a TXV with a cup of ice water and gauges but nobody has ever explained how to check modulation in a quench valve.

[sgtHVAC]

The unit I'm working on is neither the -39 or the FDECU. If it was a -39 it would make my life a lot easier because I'm used to those. This one is called a "vertical compact a/c" and it's much smaller. It's only got 3/4 tons of cooling capacity and it's about the size of small refrigerator like you would find in a hotel room. It runs with the same idea as the -39 only that it's way smaller and takes only 3.5 lbs of r-22 as opposed to the 10 lbs that the -39 took. It's designed for extreme temps and also has a quench valve to cool the compressor (which, by the way, is also a recip).

I'll get to the amp checks on the compressor soon but right now I'm ironing out a few little problems with the unit including the access ports for the guages being in bad shape.

Ambient temp in my shop is about 80F when I check. Pressures showed about 50 psi for suction and 150 for discharge. But like I said both coils were at toom temperature with frost forming at the quench line. I'm only running the unit in cooling mode. It's not a heat pump and uses electric heat for heating. When I say "pumping heat" I mean the condenser. My bad.

Thanks for the help. Good info.

[Shophound]

I checked and yes, there is a solenoid located on the quench valve line. Would you know how I can check to see if a quench valve is locked? I know how to check a TXV with a cup of ice water and gauges but nobody has ever explained how to check modulation in a quench valve.

If there's a solenoid for the quench valve, there's likely something that controls the solenoid, say a thermostat for when outdoor ambients go above its setpoint. Find out what the setpoint for this thermostat or control is, if there is one, and see if your ambient conditions are at or above that setpoint. If they are not, but the solenoid is energized (take a screwdriver and lay it across the top of the solenoid...if it sticks to the top like a magnet, the solenoid is on), then I'd be looking at the thermostat or control vs. the quench valve.

If the solenoid is de-energized when it is supposed to be, you then might suspect the solenoid to be leaking by, which would feed refrigerant to the quench valve and bypass the evaporator to an extent.

I don't know much about your machine in particular...I'm just giving you my best observation based upon what I've read in this thread so far. What I've described is a common troubleshooting technique for unfamiliar stuff....find out what it is supposed to do when it acts correctly, and then what can make it work incorrectly, and zero in on the cause. If my hunch is right, your machine is not in a high ambient condition at the moment but is getting refrigerant to the quench valve, anyway.

Above all, make the quench valve the very LAST thing you look at. Eliminate everything else first.

[usaf hvac retired]

[QUOTE=sgtHVAC;1725959]The unit I'm working on is neither the -39 or the FDECU. If it was a -39 it would make my life a lot easier because I'm used to those. This one is called a "vertical compact a/c" and it's much smaller. It's only got 3/4 tons of cooling capacity and it's about the size of small refrigerator like you would find in a hotel room. QUOTE]

I have no idea what you have there and cant offer much more help than the basic troubleshooting ideas already mentioned above. I am curious as to what its designed to cool with only 3/4 ton capacity?

[HVACLincoln]

reversing valve??

[timebuilder]

[quote=sgtHVAC;1725959]The unit I'm working on is neither the -39 or the FDECU. If it was a -39 it would make my life a lot easier because I'm used to those. This one is called a "vertical compact a/c" and it's much smaller. It's only got 3/4 tons of cooling capacity and it's about the size of small refrigerator like you would find in a hotel room. QUOTE]

I have no idea what you have there and cant offer much more help than the basic troubleshooting ideas already mentioned above. I am curious as to what its designed to cool with only 3/4 ton capacity?

Probably the officer's latrine!

[bigtime]

Make sure the strip heat is not somehow getting energized.

[mjmeis]

I work for a SQ. that has a lot of old army A/C's, and it could be the solenoid valve, were always replacing them

[markwolf]

I work for a SQ. that has a lot of old army A/C's, and it could be the solenoid valve, were always replacing them
Damn that sucks........I just realized that those "old army units"you guys are talking about are newer than the ones I worked on when I was in!lol

[mjmeis]

the ones we got were bult in the late 60's early 70's. there fun, most of the tubing joints are flanges and gaskets, that are almost imposable to get to. and on top of the solenoids going bad, those gaskets being that old like to leak

[1972torino]

Amp. draw of compressor? Close the LL service valve and see if the system "pumps down".
This it
http://www.petrotechinc.com/pdf/99028.pdf
Or this
http://www.tpub.com/content/airconditioning/TM-5-4120-287-15/css/TM-5-4120-287-15_109.htm