OM 135
PFS 155C - 315C
11
WARNING
The discharge housing of the component contains internal discharge side check
valves. If these valves are tight seating, then this housing will contain high pressure
refrigerant captured between these check valves and the discharge line shutoff valve.
The MicroTech high pressure transducer should reflect this pressure. Be careful when
servicing the discharge housing.
Liquid Injection Line Solenoid Valves
The solenoid valves that shut off refrigerant flow during a power failure, do not normally require any
maintenance.
The solenoid coil can be checked to see that the stem is magnetized when energized by touching a
screwdriver to the top of the stem. If there is no magnetization either the coil is bad or there is no
power to the coil. The solenoid coil may be removed from the valve body without opening the
refrigerant piping. For personal safety shutoff and lockout the unit power.
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 re-applying power.
Liquid injection is required during compressor operation to seal and cool the screw. A liquid injection
sensor is installed on the compressor to assure that liquid injection occurs whenever the compressor
is running. A failure of the liquid injection solenoid valve to open will cause the compressor to shut
down due to lack of liquid injection. The liquid injection solenoid valve only closes when the
compressor stops.
Electronic Expansion Valve
The expansion valve is responsible for allowing the proper amount of refrigerant to enter the
evaporator to match the cooling load. It does this by maintaining a constant superheat. (Superheat is
the difference between refrigerant temperature of the vapor as it leaves the evaporator and the
saturation temperature corresponding to the evaporator pressure).
All PFS chillers are factory set for the proper superheat. The superheat is controlled through adaptive
control strategies by the MicroTech controller and is not adjustable.
The expansion valve does not normally require maintenance, but if it requires replacement, follow the
same steps used to change a filter-dryer.
If the problem can be traced to the electric motor only, it can be unscrewed from the valve body
without removing the valve but only after pumping the unit down.
Electronic Expansion Valve Operation
There are three colored indicator LEDs (green, red, yellow) located in the control panel on the
electronic expansion valve (EXV) board. When the control panel is first powered the microprocessor
will automatically step the valve to the fully closed (shut) position and the indicator lights on the EXV
will blink in sequence. The valve can also be heard closing as it goes through the steps. The valve
will take approximately 14 seconds to go from a full open position to a full closed position.
The position of the valve can be viewed at any time by is using the MicroTech keypad through menu
3 (circuit pressures). There are a total of 760 steps between closed and full open.
