pump down for reverse cycle systems

[abbasi]

Hi there
Well I need advice on particular issue.
Somebody asked for pump down system for reverse cycle system. I tried to do it the conventional way i.e. solenoid valve was actuated by thermostat and when temperature was reached. Solenoid valve closed resulting in tripping of unit with low pressure switch. Well this works only for cooling. I am all at sea when system reverses. What can u suggest. May be a schematic drawing with description ll be helpful

Rgds

Abbasi

[NoNickName]

If one side is vacuum, when 4-way reverses the gas blast will be ramming in the pipes. I wouldn't suggest a pump down, though I don't see any reason why it shouldn't work. Just make sure compressor stops before defrosting or reversing, otherwise you most likely end up with a low pressure trip. You can't pump down if you're just with a thermostat.
You need a microprocessor which shall understand the trip as a pump down stop and not a low pressure trip. Or otherwise two different LP switches, one for pump down and the other for LP trip.
Also make sure that the condenser will not flood with liquid while pumping down, because in this case, after a reversal, it will behave like a flooded evaporator.

[abbasi]

well well well
how can we use 2 Lp's @ a time one with 0 psig and other with 32 psig setting coz 32 psig will trip prior to the latter.

[NoNickName]

well well well
how can we use 2 Lp's @ a time one with 0 psig and other with 32 psig setting coz 32 psig will trip prior to the latter.

You don't expect to pump down at 0 bar, do you?

[abbasi]

well using 2 LP switches is intricate method and i cant get the algorithm as how 2 do it, but isnt it better that for pumpdown we should revert the system 2 cooling and do it coz as u say hot gas will be ramming in the pipes,
my problem was that in cooling LP made the compressor trip once temperature was achieved but it failed to comply in heating