Heatcraft Refrigeration Products H-IM-79B - Manual (Page 20)

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CHECKING OPERATION OF EXPANSION VALVE (EEV)
To check if the expansion valve is closing properly:
Install a pressure gauge-set to suction line at the condensing unit. With the system running,
close the valve on the liquid line, at the condensing unit. The system should pumpdown and
shut off on the Low Pressure switch (LPS). If the system does not pumpdown and trip on
the LPS then the compressor valves are weak and needs to be changed.
After the system pumps-down and trip on the LPS, put the system in the service mode. This
will cause the Expansion valve to close.
Open the valve on the liquid line, at the condensing unit. The suction pressure reading on
the gauge set should not increase. If the suction pressure increases then the expansion
valve is leaking and should be changed.
The Expansion valve position can be monitored from the LED display pressing the “ MONITOR ”
button and scrolling to ESP . This will indicate the number of steps the valve is open.
This can also be checked by using the EXV test pins on the board. This is indicated by a 0 to 5
Volts DC signal. At 0 Volt the valve is closed and at 5 Volts the valve is fully open. At values
between 0 and 5 Volt, the valve will be opened proportionately.
Use the “MONITOR” button to display “ SCP ”” Evaporator Suction Pressure. Record the
pressure displayed. Start the system and observe the pressure displayed. If the pressure does
not increase, the expansion valve could be defective.
If the system is running, use the “MONITOR” button to display “ SCP ” Evaporator Suction
Pressure. Record the pressure displayed. While the system is running, press the “FORCE
SERVICE” button. Observe the pressure while the system is pumping down. The pressure
should decrease. If it does not, this indicates a defective valve.
Checking Operation of Expansion Valve
EXPANSION VALVE MOTOR WINDING RESISTANCE
If the expansion valve is suspected of not functioning properly the motor windings
resistance should be measured. This is a bipolar motor with two windings. Measure the
resistance at the pins, on top of the valve, between locations A and B or C and D. (Note
that the pins are not labeled A, B, C, D. This labeling is just for reference. Also, two of the
pins, at location B and location D, have a wider spacing between them than between
location A and C)
A• •C
• •
B D
For valve sizes 29320003 and 29320004, the resistance measured between pin locations A
and B or C and D should be approximately 336 Ohms when the valve is at 75°F.
For valve sizes 29320007, 29320008, 29320013 and 29320014, the resistance measured
between pin locations A and B or C and D should be approximately 116 Ohms when the
valve is at 75°F.
Expansion Valve
Motor Winding
Pins