charging a split system with Multi evaps
The system in question has a single condenser mounted indoors with a receiver. The system is using r134a. It has 2 air over evaporators with txv's.
clear sight glass
45 psi suction suction line at condenser 80 deg
140 psi discharge liquid line at condenser 103 deg
suction line at evap (1) 50 deg , suction at evap (2) 49 deg
liquid line at evap(1) 83 deg , Liquid line at evap (2) 85 deg
I assume there is a heat exchanger causing the temp difference from condenser to evaps.
I was called in mainly to find and fix leaks, which I did. I also cleaned the condenser.
I mainly do air conditioning and heating work, so I am puzzled why I cant get the cooler down to 45. Lowest it will go is 52 after 1 day operation.
45 psig = 50* & 50* temp @ evap = 0* superheat.
Originally Posted by heatingman
Superheat should be around 8-10* for a cooler. Can you get a pressure reading at the evaporator ? how long is your line set ?
Lineset is probably 20 feet over all. I'd have to add a tap to get exact pressure at each evaporator.
Do you think I should be adjusting TXV's? Do you think increasing the superheat will lower the evaporating pressure?
You must get that suction pressure down.
It can only be higher at the evaps.
Either the compressor is overloaded or bad. Only you can determine which.
Could a slight overcharge cause overloading?
You'd just store that excess in the receiver. Also, you'd see an elevated head pressure with an overcharge that is causing trouble.
Thanks all for the info. JP you were right, the compressor was bad. When I went back, I spoke with the owner, and he said the unit started making noise, so he shut it off. When I turned it on, the compressor would not start up. Capacitors, and start relays were working, but the rotor was locked. From my best evaluation, over the years of just having the unit topped off, and not fixed, some of the oil likely leaked out. And, every time the unit got low enough to require a recharge the compressor would just keep running, and with a low charge and lack of oil flow, the compressor wore itself out. I just found myself working on the thing on its last dying days.
I guess I missed the symptoms because I'm used to working with high temp applications, and the differential between discharge and suction looked normal to me, but as you pointed out, it wasn't because a refrigeration compressor requires a higher compression ratio.
Forget about compression ratio and think about evaporator temperature.
Can't make a 30 degree box with a 50 degree evap.
Can't make a 70 degree house with a 70-80 degree evap, either.