Conair MPA - Manual (Page 73)

UGH004/0999 microKool Portable Chillers
T
ROUBLESHOOTING
6-17
The unloader valve is located between the compressor and the
condenser on both air-cooled and water-cooled chillers. It
works only during low demand conditions, when loads are up
to 24% below normal.
During low-load conditions, the compressor cycles off. To
decrease the frequency of cycling, which is harmful to the
compressor, the microKool uses an unloader valve to channel
some of the hot refrigerant gas from the compressor directly
back into the condenser. This increases the temperature within
the condenser, simulating an increased load and keeping the
compressor running at full capacity.
You can check whether the unloader valve is working properly
by observing its behavior while the microKool is running.
Clear any alarms and restart the chiller.
Watch for the following:
❒ The unloader valve light should turn on for 2 seconds
when the compressor starts. You should hear the sole-
noid activate when the unloader valve light turns on.
❒ If the process fluid temperature is below the setpoint,
the unloader valve should stay lit until the temperature
of the process fluid exceeds the setpoint.
❒ If the process fluid temperature is above the setpoint,
the unloader valve light should turn off after 2 seconds.
You can verify that the unloader valve is inactive by
checking the refrigerant line from the solenoid valve to
the expansion valve. The line should be cool.
If the line is hot all the way to the expansion valve,
then the unloader valve is active. The solenoid valve
may be leaking, or the unloader valve may be stuck
open with power still supplied to the solenoid.
1
2
C
HECKING
T
HE
U
NLOADER
V
ALVE
NOTE: Units with the enhanced PC-2 control have two
unloader valves that work together.