Heatcraft Refrigeration Products H-IM-79D - Manual (Page 21)

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POWER FAILURES
In the event of a power failure Beacon II will automatically close the expansion valve to
prevent refrigerant from migrating throughout the system. After power returns, with 24
VAC at the board, the system will restart in the cooling mode after the four-minute hold
off period.
SPARE SENSOR TERMINALS
Beacon II provides a set of input terminals for customers who may want to monitor an
additional temperature or items such as Product Temperature. This input terminal requires
a signal from a thermistor which meets the temperature/resistance values in Table 1 on
page 22.
If a product temperature simulator is used it must meet the resistance/temperature
specification listed in TABLE 1. The temperature range for this input is –30
°
F to 140
°
F.
Sensors on the Beacon system, as supplied, will not simulate product temperature.
This input can be monitored on the LED display by using the “MONITOR” button and
scrolling to
SPt . The values displayed will be the temperature of the spare sensor.
CHECKING SENSORS
DO NOT REMOVE SENSORS FROM EVAPORATORS FOR CHECKING.
Use the monitor button to display the value the sensors are reading on the LED (suction
temp. SCt, defrost temp. dFt or room temp.). Compare this value to the measured value
with a thermometer at each of these points. If they do not match, change the sensor.
OR
The sensors can be checked for their proper operation by placing it in a cup of ice water.
Stir the ice water and measure the resistance of the sensor. At 32
°
F the resistance should
be 32,650 ohms. If it is higher or lower by 5,000 ohms approximately, the sensor should be
replaced.
Power Failures
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 is 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.