carrier 2-stage rtu

[dhaynes]

was wondering if u guys could help me out with this one. we do mostly residential and light commercial work at the company where i am employed. here is my dilemma: hardware store with a carrier 48tj rtu not performing adequately, unit has a small leak in circuit #1. my suction pressure is 79 p.s.i.g. with a suction temp. of 79-80 degrees, but the chart says that i should be closer to 62 degress. I dont want to add more refrigerant because the discharge is running at about 375 psig. the unit does have hp and lp cutouts. the condenser coil doesnt look very dirty at all but i know looks can be decieving. this all took place at about 5:30 pm on friday and all the tech support is out for the weekend, any help would be greatly appreciated. unit is approximately 4-5 yrs old.

[eastcreek]

...you've got 33 degrees of superheat, what's your sub-cool?

[dhaynes]

i didnt calculate subcool, was trying to get my superheat within range first, but i know that that is too much superheat for the conditions present, i need approximately 12 degrees of superheat

[maxster]

your suction is being pushed by the hi discharge the condenser needs a good inside/out cleaning first thing then the leak and check the SH/SUB.what was your ambient that day going into the condenser

[psychometric]

those carrier coils never look that dirty until you take a hose and coil cleaner to them. That head pressure is way too high, so clean that coil good.

[dhaynes]

ambient was 94-95....circuit #2 runs perfect is why i thought that the coil wasnt causing the problem....ill take your advice and clean it anyway.....circuit #2 has exactly 12 degrees of superheat, also something i forgot to add was that when i removed the access door to get the m# and s#, my suction temp shot down very quickly, what caused this?....but when i put the panel back on it went back up to 79 degrees

[joey791]

Not familiar with Carrier model numbers but if your running that head and you have 2 compressors, first thing you need to do is go back and split and wash the condenser coils then start with superheat and subcooling.

[matt8085]

Well, did you take the condensor panel off while it was running to get model and serial? If so, what did you expect to happen? Split those coils and wash them good.

[dhaynes]

what do you mean by, "splitting the coils"?

[lwarren]

Raise the top of the unit on the cond end. You will be able to get on one end of the coil and pull the front coil away from the rear coil. The rear coil will probably be covered with dirt.

[dhaynes]

thanks to all for the advice. i will put it to use and go from there, and then let u guys know the outcome. About the comment of taking the panel off while the unit is running to retrieve m$s#. did this raise my head pressure, in turn forcing it through the metering device, which brought my suct. temp down?

[lwarren]

If you took your readings (pressures) with the compressor acsess panel off, then your readings will not be acurate because of the air that bypassed the cond coil.

[service guy]

What was the head on circuit #2? I'm leaning towards overchage of circuit #1 and a dirty coil.