58
IM 1131-2
System Service
System Service
System Service
NOTE: Anyone servicing this equipment must comply with
the requirements set forth by the EPA concerning refrigerant
reclamation and venting.
Filter-Driers
To change the filter-drier, pump the unit down (with the
compressor running) by closing the manual liquid line shutoff
valve(s). The unit will start pumping down until it reaches the
low-pressure cutoff setting of 58 psi.
Close the discharge valve. Remove the refrigerant in the liquid
line with a recovery unit to EPA required pressure. Remove
and replace the filter-drier(s). Evacuate the lines through the
liquid line manual shutoff valve(s) to remove noncondensables
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 valve(s), which are responsible for
automatic pumpdown during normal unit operation, do not
normally require any maintenance. However, in the event of
failure they can require replacement of the solenoid coil or of
the entire valve assembly.
The solenoid coil can be removed from the valve body without
opening the refrigerant piping by moving pumpdown switch
PS1 or PS2 to the "manual" position.
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
returning the pumpdown switch to the "auto pumpdown"
position.
To replace the entire solenoid valve, follow the steps for
changing a filter-drier.
Thermostatic Expansion 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). All WGZ chillers
are factory set for between 8°F and 12°F (4.4°C to 6.7°C)
superheat at full load.
To increase the superheat setting of the valve, remove 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 and counterclockwise to reduce
superheat. Allow time for system rebalance after each
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 changing
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.
Figure 30: Thermostatic Expansion Valve
Note: Superheat will vary with compressor unloading, but
should be approximately as follows: between 8°F and 12°F
(4.4°C and 6.7°C) at full load; between 6°F and 10°F at part
load.
Water-cooled Condenser
The condenser is of the shell-and-tube type with water flowing
through the tubes and refrigerant in the shell. Integral
subcoolers are incorporated on all units. All condensers are
equipped with 450 psig (2790 kPa) relief valves. Normal tube
cleaning procedures can be followed.
Evaporator
The evaporators are sealed, brazed-stainless steel plate unit. or
DX shell-and-tube. Normally no service work is required on
the evaporator.
DANGER
Service on this equipment is to be performed only by qualified
refrigeration personnel. Causes for repeated tripping of equipment
protection controls must be investigated and corrected. Disconnect all
power before doing any service inside the unit or serious personal
injury or death can occur.
CAUTION
Adjustment of expansion valve should only be performed by a qualified
service technician. Failure to do so can result in improper unit
operation.
