500 psig at discharge, 250 at LLSV

[wdshea]

likely restriction, or is this possible?

5 ton trane split system, condenser is on the roof. system cools a server room. at 55* ambient, i have ~100psig liquid pressure, close to zero subcooling, and amps in excess of RLA at the compressor.

Any ideas? i'm starting to think air in system.

p.s. 20* evaporator, with excessive superheat (TXV).

[jayguy]

you must have a restriction otherwise you would have nearly 500 psig at the LL solenoid valve too. not to say that you don't have air too, but your biggest problem is a restriction of some sort.

[bunny]

You state 250 at the LLSV and then say ~100 liquid pressure.

Which is it???

[wdshea]

sorry, it had been a long day. the 100 psig was after i bypassed the fan cycle control so the unit would run. the 500/250 was what i was getting, but since the fan cycle control cut in was too high, the system couldn't run. i don't even know what the cut in is, couldn't read it.

[wdshea]

if it were air, could i pump down the system, and check the pressure against my PT chart? i realize that the LL Schraeder Valve would be blocked by the LL Service valve (when closed), but there is a schraeder on the discharge manifold. what do ya'll think?

[valdelocc]

if it were air, could i pump down the system, and check the pressure against my PT chart? i realize that the LL Schraeder Valve would be blocked by the LL Service valve (when closed), but there is a schraeder on the discharge manifold. what do ya'll think?

sell them a new unit, tell the customer tranes are junk, parts are expensive and the problem could be electrical,mechanical or both combined. that approach has never fail me, trust on this one.

[wdshea]

...


first of all, i don't want to sell them something they don't need, second i want to know why this system is acting the way it is.

third, i assume you are kidding

[air1]

Is there anything between the discharge and LLSV that could cause a restriction? Filter/Drier perhaps?
To remove air I was taught to recover the refrigerant into a clean tank and let it sit for a while. Then bleed the air out of the gas valve. This way you could weigh out the charge to verify charge, remove any non-condensable gases, and weigh the correct charge in to eliminate the charge as a possible problem.

[pipefitter636]

R-22,407C ,410A?? Check valve in discharge line?? Compressor on the the roof or at the air handler??

Model and serial number of unit??

More info please...

[wdshea]

the thing is, i was hoping to save time by pumping all the refrigerant into the condenser and essentially do the same thing... there is a cheap copper FD that was in the unit, then another filter drier out of the unit... though no temp drop on the internal FD.

[air1]

the thing is, i was hoping to save time by pumping all the refrigerant into the condenser and essentially do the same thing... there is a cheap copper FD that was in the unit, then another filter drier out of the unit... though no temp drop on the internal FD.

You could still have a substantial pressure drop across the FD without a noticeable temperature drop. There was a thread about this very issue recently.

[qwerty hvac]

sell them a new unit, tell the customer tranes are junk, parts are expensive and the problem could be electrical,mechanical or both combined. that approach has never fail me, trust on this one.

Why sell a new unit when you can fix the old one? Must be a glorified sales tech!


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[qwerty hvac]

You could still have a substantial pressure drop across the FD without a noticeable temperature drop. There was a thread about this very issue recently.

X2


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[beenthere]

Fan cycler was set too high to leave the condenser run? Good chance its not working and is the cause of the restriction.

[wdshea]

i don't think it is the fan cycle so much as the pressure issue. the fan cycle is detecting the liquid pressure (which is too low), and isn't cycling the fan on soon enough, by the time it does, the compressor relief is already bypassing.

[grkmano]

What kind if unit is this your working on?

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[valdelocc]

Why sell a new unit when you can fix the old one? Must be a glorified sales tech!


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Highly glorified must add!! thats why I make the big bucks

[Trane Tech NYC]

This should be a good one, the high superheat indicates a starving evaporator but the lack of subcooling is trouble.

The high excess compressor amperage is obviously telling you there is an issue. Im assuming this is a R22 system. Is it metering correctly? Can you range the SH? Your restriction could wind up being the TXV if its not the drier, kinked lines or the obvious.

[Nuclrchiller]

It's been over a week now. Hopefully it's solved. Hopefully we'll hear about it...

[wdshea]

Problem solved!

Internal filter drier was restricting flow. You know the ones i'm talking about, those POS copper FD's that trane put inside the unit. The mesh had actually come apart and the dessicant had come out of it.

Anyway, long story short, dumbass had low pressures, so he just kept adding refrigerant until the suction got above freezing.

Anyway, i speculate that because the system was so grossly overcharged there wasnt a temp drop across the internal FD. (There wasnt, i checked)

I recovered 18.5lbs of refrigerant, factory charge is 7.75, and i charged it to 13.75. System is running well, but there are some other issues that need attention.