60 ton built up

[ariztech]

first timer here...i`ve stopped by and read several times. meanwhile... here`s the stats two 15 ton 06e`s capacity control on one bank each compressor.retail store.first stage calls 70over250.tower pump on when call for cooling tower fan on pressure control cut in 280 cut out 230.system runs fine. second stage calls.after tower fan cycles once or twice, my headpressure and back pressure on first stage starts droping
down 35-40suc. and swings back up to 70, 200-210head and swings back up to 250.the problem is i am tripping out on oil lube saftey..all the oils in the evap..short of a drive on the tower fan any ideas...? 74 in space

[freonrick]

you need to control the tower fan by water temperature.

[gasnowman]

sounds like a compressor loading, or capacity issue. Are you working on a water or air cooled system?

[ariztech]

what makes temp better than pressure...?

it`s water...

[gasnowman]

water temperature controls may be better for compressor staging and condenser loop stabilization for low and high load conditions verse pressure. How many times are you cycling the condenser fan an hour on pressure verse temperature........just a thought

[hot wired]

does this compressor have a unloader or hot gas bypass?

[ariztech]

this compressor has an unloader....set to load at about 73 and unload at 65....

[ariztech]

two seperate compressors..one evap condenser..one fan motor
oh yea sight glass 1/3 to 1/2 full..

there is no check valve..using refrigerant as the means to
bring back the oil...
i think vfd is my only answer..to keep head pressure constant custumer will just have to get off the wallet..

thank you guys for all your suggestions...

[stopro1]

has the right idea- tower fan should be controlled by water temp entering condenser (typ set at 90). Sounds like you may have 2nd stage circuit bringing on fan by it's head pressure when the first stage's head is much lower due to low charge or other problem. Water temp control eliminates a conflict between stage requirements (although both should be similar if both are working properly). Also sounds like unloader is set to high- shouldn't unload until 55-58 lbs of suction with a 10-15 pound diff to reload.