5 Ton Payne A/C Not Cooiling

[renegadejd]

- A/C is barely cooling. Going into Therm overload. The high side line was same temp from port to piston. At the piston it would freeze over. It also had a port installed about 1 1/2 " - 2" before piston that looked like a poor install, the port line was a size smaller than the line. So I thought a restriction in the piston. Opened it up and didn't see anything obvious so I cut out the poorly installed port and put in about 3" correct size line in its place. I attached the piston back to the evap blew out my lines (low and high side), reconnected all my lines. Blew out system both ways through service ports with stems removed. Pulled vac for about an hour and a half, let set for 2 hrs, checked and vac was still where I left it (30) no budge. Disconnected hoses put valves back in reconnected hoses pulled vac for an hour. Charged unit and this is where I'm at now........... basically the same symptoms but piston is not freezing (only because the charge is lower than previous) both before and now suction lines aren't sweating, and plenty of condensation.

Amb Air 88-90

-
54 PSI
EVAP SAT 28
Suction Temp 82
Superheat 54

-
PSI 280
Cond SAT 126
Liq Temp 112
Subcool 14

Any and all help is greatly appreciated. Thanks

[renegadejd]

I did blow out the lines with piston removed and open and also blew them out after I closed the system in both directions. I did not see any strainer. Thanks for your help. I'll take another look and see if I can find anything else.

[nomadpeo]

could you clarify a couple of things ? the added 'port' in question.....was this a peice of piping smaller than 3/8 inch prior to the metering device that you removed ? unless i misunderstand, i'm assuming you were concerned it was creating an extra restriction.

you didn't mention filter/drier or vacuum gage. you clearly have a starved evap, possibly due to a restriction. obviously if you charge until the sh is in an acceptable range (5 to 20 nominal), the discharge pressure would probably be out of sight. the following checklist includes some standard refrigeration items for your consideration. rule out variables and you will pinpoint the problem. there are only two possible restriction points, but make sure all other conditions are correct.

- verify no leaks. a vacuum pump will pull in air/water through a leak.
- change filter/drier whenever system is opened to the atmosphere. if it is restricted even a little bit, the added restriction will cause the sp to drop and dp to rise. the evaporator will starve and the sh will rise.
-always use a vacuum gauge when pulling a vacuum. air is one of the non-condensables, water is the other. a proper vacuum will boil water, but without a vacuum gauge, you do not know if you still have water.
-verify clean condenser, evaporator and filter. verify matched evap and cu. verify correct ducts. verify no ra leaks. correct readings depend upon normal conditions and correct design.
-verify good run capacitor. extended running time with high dp and high sh is probably causing the ol, but do the checks. there are several ways you can verify the capacitor. you can use an upper end digital meter or analog meter, you can verify mfd against rating, you can do a running capacitor test (let me know if you need a formula). first, though, check the compressor amps against rla rating.

sounds like the problem may be a restricted liquid line filter drier. measure the temp of the liquid line entering and leaving e filter/drier. if you see any difference, you have an added restriction causing low sp / starved evap / high sh. for the same reason, the dp goes up. the compressor pumps at a constant rate. the normal restriction by design at the md causes the differential between the low and high sides. extra restriction causes that differential to be exagerated, resulting in reduced saturation (liquid/vapor combination) in the evaporator as well as backed up liquid driving the dp up. if the filter/drier is not restricted, call carrier and verify the piston is the correct size. if it is, the other possible culprits include system design (evap mismatch) and non-condensables (water and/or air).

let us know what you find out.

[renegadejd]

WOW... That is some great detailed help. I really needed that. However the compressor went out night before last. I am replacing the compressor (scroll) tomorrow. But I can use this help to help make sure eveything is good before the compressor is replaced and started. I am sorry but I don't know what some things mean can you tell me?

sp to drop and dp to rise--- dp??
verify no ra leaks--- ra??
causing the ol, but do the checks --- ol??
low sp / starved evap / high sh --- sp??
design at the md causes --- md??


could you clarify a couple of things ? the added 'port' in question.....was this a peice of piping smaller than 3/8 inch prior to the metering device that you removed ? unless i misunderstand, i'm assuming you were concerned it was creating an extra restriction.
This is true.................... mainly I was concerend about the sloppy install, then the risk of restriction.



you didn't mention filter/drier or vacuum gage
There is a suction dryer installed, I plan to remove it tomorrow.
no vacuum/micron gauge, yes I know a no no... but i'm trying to do the best with what I have.


-always use a vacuum gauge when pulling a vacuum. air is one of the non-condensables, water is the other. a proper vacuum will boil water, but without a vacuum gauge, you do not know if you still have water.
if I can get one tomorrow, how do I use it to tell water is gone?


Thanks for all of your help. It is greatly appreciated.

[nomadpeo]

sp to drop and dp to rise--- dp?? discharge pressure
verify no ra leaks--- ra?? return air temperature
causing the ol, but do the checks --- ol?? overload (internal to the compressor - temperature sensative
low sp / starved evap / high sh --- sp?? suction pressure
design at the md causes --- md?? metering device

[kaliya]

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this site use of all the would and system news and helps known every one...........

[heatseeker]

can you type in english please?

[moshei]

Very nice information and site...,
It's a big help..!!
Thanks for sharing....!

[heatseeker]

Ilk bet you had the same problems after you replaced the compressor.