Liebert help please

[refrtech]

Liebert model # FH600C-AAES

This is a dual cooling unit . Primary cooling is done by the chilled water coil with back up DX cooling . My question is this , what makes the DX cooling run ? There is an aquastat that is installed on the main chilled water line and I have constant 42F glycol . Why does the DX cooling run when it should be using the chilled water coil . I know it has to do with the aquastat but not exctly sure when or why it would kick over to DX .

Thanks :)

[maxster]

that "chilled water" your refering to is the glycol from the condensers on the roof if your ambient is low enough to cool it.your doing return air sensing on your setpoint so the unit will econo-cool and after a fixed time if the setpoint isn't made the valve will swing the exiting glycol thru the condenser at say 53F from the return air heat gain and the DX will run staging up to make the setpoint on that return.if you can tweek that glycol temp setpoint down to maintain 40F your compressors will stay off as long as your ambient can do it...up on the roof.so in the winter you want the condenser fans to run if the line gets warm to maintain that 40F see if you condensers have that fan option...you should have some TC-1 temp controls inside the rooftop units that are strapped to the headers

[service guy]

DX will also run to dehumidify the air.

[ZeroCool]

He has a chilled water coil with a dx coil built in across it for dual cooling capability. I don't remember exactly but I believe that it is if the aqua stat senses the chw supply 3 deg below return it assumes you have full chw capability. I think there are a couple other options that will make it switch. Call your local Liebert rep and get their tech support number and call. They are very sharp on their product.

[maxster]

so if that is chilled water is the return going out thru the condensers for the DX call..say anything above 53F water OKs the compressors to run

[refrtech]

You are correct Zero Cool . I spoke with Liebert and it is set to call for DX if the CW supply is 3F below return .