SERVICE
NOTE: Service on this equipment is to be performed by qualified refrigeration service per-
sonnel. Causes for repeated tripping of safety controls must be investigated and corrected.
CAUTION: Disconnect all power before doing any service inside the unit.
FILTER-DRIERS
To change the filter-drier, pump the unit down by moving
pumpdown
switches PS1 and PS2 to the “manual
pump-
down” position.
trol. Close the manual liquid line shutoff valve(s). Turn power
to the unit back on and restart the unit by moving the control
switch
S1
to the “on” position. The unit will start pumping
down past the low pressure setting. When the evaporator
pressure reaches O-5 psig, move control switch
S1
to the
“off” position.
Move the control switch
S1
to the “off” position. Turn off all
power to the unit and install jumpers across the terminals
shown in the table. This will jump out the low pressure
con-
Frontseat the suction line King valve(s). Remove and
replace the filter-drier(s). Evacuate the lines through the
li-
quid line manual shutoff valve(s) to remove non-condensables
that may have entered during filter replacement. A leak check
is recommended before returning the unit to operation.
LIQUID LINE SOLENOID VALVE
The liquid line solenoid valves, which are responsible for
automatic
pumpdown
during normal unit operation, do not
normally require any maintenance. They may, however, re-
quire replacement of the solenoid coil or of the entire valve
assembly.
The solenoid coil may be removed from the valve body
without opening the refrigerant piping by moving
pumpdown
switches PS1 and PS2 to the “manual pumpdown” position.
THERMOSTATICEXPANSION VALVE
The expansion valve is responsible for allowing the proper
amount of refrigerant to enter the evaporator regardless of
cooling load. It does this by maintaining a constant superheat.
(Superheat is the difference between refrigerant temperature
as it leaves the evaporator and the saturation temperature
corresponding to the evaporator pressure.) Typically,
superheat should run in the range of 10” F to 15” F. On valves
purchased through McQuay, the superheat setting can be
adjusted by removing the cap at the bottom of the valve to
expose the adjustment screw. Turn the screw clockwise
(when viewed from the adjustment screw end) to increase
the superheat setting and counterclockwise
superheat. Allow time for system rebalance
superheat adjustment.
The expansion valve, like the solenoid valve,
should not
normally require replacement, but if it does, the unit must
be pumped down by following the steps involved when chang-
ing a filter-drier.
If the problem can be traced to the power element only,
it can be unscrewed from the valve body without removing
the valve, but only after pumping the unit down.
INLET
The coil can then be removed from the valve body by simply
removing a nut or snap-ring located at the top of the coil. The
coil can then be slipped off its mounting stud for replacement.
Be sure to replace the coil on its mounting stud before retur-
ning
pumpdown
switches
PS1
and PS2 to the “auto
pump-
down” position.
To replace the entire solenoid valve follow the steps in-
volved when changing a filter-drier.
to reduce
after each
POWER ELEMENT
(CONTAINS DIAPHRAGM)
OUTLET
ADJUSTMENT SCREW
/-
CAP
Page 50 I IM 269
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