26
Beacon II Controller
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 pump-down and shut off on
the Low Pressure switch (LPS). If the system does not pump-down 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 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
signa. 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.
Expansion Valve Motor Winding ResistanceIf 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.)
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 valve is at 75°F.
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.
Measuring the DC volt of the EXV TEST pins, on the board, will also indicate if the expansion valve is open or
close. 0 volts DC indicates the valve us closed, 5 volts DC indicates the valve is fully open. A Values between
0 and 5 volts indicates how much the valve is open or close.
Figure 16.