Beacon Ii Controller - Heatcraft Refrigeration Products II Installation & Operating Instructions Manual

Mccu condensing units

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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 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 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.)

Figure 16.

Expansion Valve

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.