24
Beacon II Controller
Checking Operation Of Expansion Valve
(EEV)
1. 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
receiver, 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, turn off the
power to the Beacon II board, then turn the power back on. This
will cause the Expansion valve to close.
Open the valve on the liquid receiver, 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.
2. 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 Volts the valve is closed and at 5 Volts the valve is
fully open. At values between 0 and 5 Volts, the valve
will be opened proportionately.
3. 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.
4. 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.
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).
Expansion Valve Motor Winding Resistance
Resistance reading at 150
at 75° F
“C” is largest spade
Measuring resistance between locations A and C or B and D will always show “Open” because these
locations are between the motor windings.
When the valve is opening or closing, the voltage measured between A and B or C and D should be between
20 to 22 VAC.