I have a question concerning operation of a Liebert DX computer room unit during a condenser fan failure.
Situation:
Communications room, two upflow Liebert DX 15 ton units.
The units are configured as a team with lead unit switching every two weeks.
Two compressors in each unit, two refrigerant circuits, air cooled condensers (also Liebert) with three fans.
One fan is pressure controlled, variable speed, two are outdoor temperature controlled and constant speed.
The variable speed motor seized up and the one compressor calling at the time tripped on high head.
The tech called to the facility noted the fan failure and then disabled one of the two compressors, when asked why he said “you cant run both compressors on only two fans”
I explained that the coils are length wise on the condenser not stacked therefore all three fans draw air over both circuits.
He said if he left both compressors enabled it would trip on high head again.
The outdoor temperatures have cooled down since this event, fan motor still on order.
My question is: Am i correct when I stated the one circuit does not affect the condensing temperature/head pressure of the other and given that we have cooler weather both compressors should be enabled?
If I am incorrect what is the reason for this?
The other concern I have (and got a seemingly strange answer for) is that the setpoints are 68 (return air) and I do not need the room to be that cold. The techs foreman said if we raise the setpoint the head pressure will be higher than if we run the units at 68.
Again, I can see the pressures being somewhat different running at 68 vs 74 but temps at 74 would reduce the number of compressors online.
The usual room conditions usually have two compressors in the lead unit running continuously and the standby unit calling with one more compressor periodically.
Thoughts on this?
In addition to helping me understand this what are your thoughts on continuing operation while a motor is on order?
Thanks.