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if your distributors were plugged then the result would be low suction high superheat and high subcool also it would probably freece at the distributors. did you weigh in the charge if not pull your charge and weigh it in per the data plate this can eliminate charge as a problem. what is the temp of the air entering the unit. look for unit sucking in hot air from somewhere. your not right by an exhaust fan or something are you.

I would see if you can install a TXV kit. Ive had several small Trane RTU's Do the same thing. Your metering device is not allowing enough refrigerant through. I blew the rail out twice and it didnt fix it. Ordered a TXV kit and it worked perfect. Did u use new gas to assure it wasnt contaminated, people add NU-22 and MO-99 to top it off. It sounds like your drier might have come apart inside and plugged the orfices. Tech support told me this can be due to high ambient temp and a dirty condenser, the compressor gets hot and bakes the oil, plugs the drier and either passes through it or plugs it and the high pressure breaks down the inside of the drier.

Originally Posted by deux

*lots of dust came out*??????

I am not saying nutting.

oh man missed that part.... hopefully out of the condenser.... mmmmmm

*lots of dust came out*??????

I am not saying nutting.

300 head and 79 suction i would hiss as well.... is condenser clean...if it is the unit is overcharged

Also i have to say the compressor is noisy not hissing but kind of hammering but not too bad, i hear compressors like that before and still working. And when the unit is disconnected pressures equalize too fast.

superheat too high, but pressures look normal...

I checked a 10 ton pkg unit with 2 independent compressor, 2 stage, 2 circuits. One compressor was cooling just fine but not the other one. Unit is an international comfort PGS120H250.Bad compressor was like this:
Low side press: 35psi
High side : something around 190-200psi
Suction tube temperature: 95ºf
Indoor air temp:77ºf
Outside air temp:88ºf
So i recovered, vacc, check for leak... leak schrader valve, replace it and got rid of the leak. Then unit need 3.6lb of refrigerant, charged it and pressures were like this:

Low side press: 79psi
High side press: 300psi
Suction tube temp: 89ºf
indoor temp: 75º-77ºf
outside temp: 90º

Cause the superheat was high i tough the evap was starving cause a restriction, so i replaced the liquid line filter, blow the lines w/nitrogene (lots of dust like oxidation came out) vacc, and charged it again and is doing almost the same thing, pressures that seem to be ok but not cooling and suction temp to high.
Im thinking to replace the header tube for the evaporator, cause it does not has txv or piston, is like a lot of work pulling the evap out welding and all that crap. My question is if it is really the header tube that is resticted or IT COULD BE SOMETHING ELSE??? I was wandering if it could be the internal compressor valves... thanks for the help...