Looking for a second opinion on this situation. Went to call and unit was not iced up, must have just came off defrost cycle or customer had it off and only turned it on when i got there. Asked customer if unit ever had problems or been serviced before, and of course said no. Ambient temp in cooler was 0-2 degrees F, but customer complained of ice cream melting. Upon inspection of condesing unit, found unit to be running to be what seemed normally. inspected condensing unit for about 30 min looking for any switches that could be bound or have burnt contacts and everything seemed alright, switches were all closed when they were supposed to . Checked pressures and all controls to see what may have opened and no switches were open. Suction pressure was high and discharge temp was a bit low. went downstairs to evap and evap coil was only iced up around the side of the unit where the txv and solenoid were located. went back upstairs to check pressures, and pressure dropped and unit shut off and went into defrost(fan cycling system w/defrost timer). did this about three times and now amb temp in cooler is at about 32 degrees and unit is still not entirely defrosting or cooling properly. It went into late night (16:30-18:00 (length of time spent) and customer did not want to pay OT so i'm going back tomorrow. oh yea, and compressor had been replaced(looked too new in such a decrepit unit) without suction line filter drier -_-, didn't check for acid in system but theres time for that tomorrow.
system is r502, 3ph, 208/230vac.
I'm thinking its one of these things:
1) low on refrigerant (didn't want to jump to conclusions because i knew super-heat/ sub-cooling would be off with unit frozen. wait till tomorrow to check)
2)moisture in refrigerant, plugging txv and thats why that side is icing up. need to recover refrigerant and replace with virgin refrigerant
3) Txv going bad, losing thermal charge
4) bad pumpdown solenoid
5) bad compressor valves which indicate high back pressure?
-with this, would the compressor be drawing high amps?
6) fan cycling control binding up? i don't see how that could do it though. the compressor would be sending hot gas thru the evaporator essentially keeping it in the defrost cycle, right?
I have 5 yrs experience installing furnaces, a/c/ and ductwork, but I'm new to servicing refrigeration so help would be appreciated. Thanks for any and all help.