I came across a system the other day that looks as though a mistake was made in the control scenario. Water cooled R12 recip. compressor. 3 ton TXV, external equalized. Liquid line solenoid valve. Hot gas solenoid valve feeds hot gas regulator to side inlet of outlet of TXV. Temperature control is done by pressure switch on suction of compressor. When command to cool is issued ALL solenoids are energized. Now pressure
switch has control of the compressor start/stop.
Pressure switch set to maintain 5-8*C space temp.
As space temp. drops suction pressure will drop, but hot gas kicks in and raises suction pressure
so unit will never satisfy low pressure switch. There is a hand valve feeding the hot gas solenoid that if closed allows system to pull down and cycle on pressure switch. I think what happened here is that unit was controlled by temp.
at one time and someone decided to use pressure type control but never took the hot gas into consideration. Current control scenario doesn't make sense. How can you have pressure control and hot gas bypass at the same time? I have some ideas
floating around. One scenario that surfaced was that maybe they were regulating that hand valve to feed a little hot gas in to keep the evap. active and promote some oil return? Note that when the pressure switch satisfies the solenoids remain energized. Only thing that kills power to them and starter is computer command to stop cooling, also stops evap. blower. Soliciting
thoughts, comments, concerns from fellow fridgeheads.
Mike Hopkins