walk-in cold room.

[kerrcell]

HI guys,
I have been on this cold room(frezer -20),which somehow a cowboy have replaced a semi hermetic with a scroll ! Besides this,had to rewire all from new as can imagine what ! Now I need to ask about the way the compressor shall stop after a thermostat signal.At present is turning off the contactor for the compressor and condenser fan.I am in the idea of installing a high and low pressure switches as there is not at present ,and the thermostat turn off the liquid line solenoid,to take a pump down,and trip on low pressure.I am afraid that the oil will not be returned back on a normal cycling.Is it effective to try to collect oil back with refrigerant this way.Does the scroll equalise the same as the reciprocating ? My concern was since there was Not installed a suction accumulator.I don't think that this compressor will last for long !! Any ideas ?

[martinw58]

fit pressure switches and wire system to pump down and stop on low pressure switch

[kerrcell]

Martinw58,
Will it be successful to collect oil from evaporator,because I am afraid that during time will practically force gradually oil out,ending with no oil in compr.Since it's a scroll does it affect from the suction side ?

[flyinkiwi]

So long as velocity in the pipe is correct, (Does the displacement of the scroll match that of the semi?) oil return shouldn't be a problem.

Does the system have an oil sep fitted?

Additionally, be careful with your LP cut out setting, as extended operation of a scroll at low mass flow is a recipe for disaster. Better to leave the LP as high as you possibly can without it cycling.

No HP/LP?

[kerrcell]

Flyinkiwi,
Unfortunately as I said,there was someone that replaced the semi hermetic compressor with this scroll!Have no acess to the original compressor,so cannot state that it is adequate for it's capacity.There is no oil separator in system.With regards to the low pressure switch,shall I set to 1/2 Bar.System runs on R22!

[PRESS]

Hi,

Martinw58 has sugested a good way of controling this unit. Remember that when your thermostat energizes the liquid line solenid valve agin when there is need for cooling you release high pressure gas into the evaporator which should push most of the oil back to the compressor. However should you have your fears it is not bad practice to install an oil seperator just to give yourself comfort.

[monkey spanners]

Hi Kerrcell,

If the scroll is sized right for the duty and application then it should be ok. I have had to fit different make and/or models when the correct compressor has been out of stock and the system needs to be running as soon as possible.

Fit a crank case heater if none is fitted now. If you run it on pumpdown, as Flyinkiwi says, set the lp to as high a cut out as practical, and a wide differential too to prevent short cycling. Or you could just shut the solenoid when the compressor is off, this will help stop liquid migration when the comp is off, especially if the solenoid is near the txv.

Jon

[kerrcell]

HI Monkey spanners,
I shall fit a crancase heater around comp.There isn't actually.I think will stick also to feed thermostat output to control solenoid of liquid line,then to trip system on low pressure switch.The solenoid is around 3 mtrs from exp.valve.