Defrost Control Board Operation and Testing

Indoor Blower — Set the thermostat function switch to COOLING and the fan switch to ON. Verify that the indoor blower is operating and that airﬂow is not restricted. Set the fan switch back to AUTO.

Low-Pressure Switch — A low-pressure switch is factory-installed (see attached). This switch is located in the suction line internal to the out- door unit. The switch is designed to protect the compressor from a loss of charge. Under normal conditions, the switch is closed. If the suction pressure falls below 5 psig, then the switch will open and de-energize the outdoor unit. The switch will close again once the suction pressure increases above 20 psig. Please note that the switch interrupts the thermostat inputs to the unit. Thus, when the switch opens and then closes, there will be a 5 minute short cycling delay before the outdoor unit will energize.

Cooling — Gradually lower the thermostat temperature setpoint below the actual room temperature and observe that the outdoor unit and indoor blower energize. Feel the air being circulated by the indoor blower and verify that it is cooler than ambient temperature. Listen for any unusual noises. If present, locate and determine the source of the noise and correct as necessary.

Short Cycle Protection — With the system operating in COOLING mode, note the setpoint temperature setting of the thermostat, and gradually raise the setpoint temperature until the outdoor unit and indoor blower de-energize. Immediately lower the setpoint temperature of the thermostat to its original setting and verify that the indoor blower is energized and that the outdoor unit remains de-energized. Verify that, after approximately 5 minutes, the outdoor unit energizes and that the temperature of the air supplied to the facility is cooler than ambient temperature.

Heating — Lower the thermostat setpoint temperature to the lowest obtainable setting and set the thermostat function switch to HEATING. The indoor blower and outdoor unit should stop running.After a minimum of ﬁve minutes, increase the setpoint temperature of the thermostat to the maximum setting.Verify that the outdoor unit and

indoor blower have energized. Feel the air being circulated by the indoor blower and verify that it is warmer than ambient temperature. Listen for any unusual noises. If present, locate and determine the source of the noise and correct as necessary.

NOTE: Other sources for heating (i.e.: electric furnace, fossil fuel furnace, air handler with electric heat options, etc.) that interface with the unit should be functionally checked to verify system operation and compatibility. Refer to the installation instructions for this equipment and perform a functional checkout in accordance with the manufacturer’s instructions.

Defrost Cycle Timer — The defrost cycle timer controls the accumulated run time interval of the hot gas defrost after the defrost sensor closes. It is located in the upper right corner of the defrost control board.Three interval settings are available: 30 minutes, 60 minutes, and 90 minutes. Time setting selection is dependent on the climate where the unit is being installed.The default defrost cycle timer is set to 30 minutes.To adjust the cycle time, move the jumper to cover the two pins directly adjacent to the desired cycle time.

Example 1. Dry climate of Southern Arizona. A 90 minute setting is recommended.

Example 2. Moist climate of Seattle, Washington. A 30 minute setting is recommended.

High-Pressure Switch — A high-pressure switch is factory-installed and located in the liquid line internal to the outdoor unit. The switch is designed to protect the system when very high pressures occur during abnormal conditions. Under normal conditions, the switch is closed. If the liquid pressure rises above 425 psig, then the switch will open and de-energize the outdoor unit. The switch will close again once the liquid pressure decreases to 350 psig.Thus, when the switch opens and then closes, there will be a 5 minute short cycling delay before the outdoor unit will energize.

DEFROST CONTROL BOARD OPERATION AND TESTING

1.Terminals “R”-”C” must have 24±V present between them in order for the time delay and defrost sequences to be operational.