Whirlpool W4GH6 Sequence of Operation, Cooling Cycle, Heating Cycle, Defrost Cycle

SEQUENCE OF OPERATION

Cooling Cycle

Upon cooling demand, the thermostat closes circuit R to O and Y. Closing R to O and Y energizes the reversing valve for cooling operation and closes the heat pump contactor, starting the compressor and outdoor fan. The thermostat automatically closes R to G circuit, which also brings on the indoor fan at the same time. Upon satisfying cooling demand, the thermostat will open the above circuits and open the main contactor, stopping the compressor and outdoor fan. If the indoor unit is equipped with a delay timer, the blower will continue to operate for 60 to 90 seconds, which improves system efficiency.

Heating Cycle

Upon heating demand, the thermostat closes circuit R to Y, which closes the heat pump contactor, starting the compressor and outdoor fan. The reversing valve is not energized in the heating mode. The thermostat again automatically brings on the indoor fan at the same time. Upon satisfying heating demand, the thermostat opens the above circuits and stops heat pump operation.

Defrost Cycle

If the outdoor ambient conditions are such that frost forms on the outdoor coil, the defrost control monitors a defrost cycle. It then runs the defrost cycle as ambient temperatures require.

The defrost control is time/temperature initiated and temperature terminated with a maximum defrost time (time-out) of 10 minutes. The time between defrost cycles is preset at 60-minute intervals at the factory, but can be field adjusted between 30, 60, or

90 minutes. To adjust the time period between defrost cycles, see “Adjust Time Between Defrost Cycles.”

The defrost control will initiate a defrost cycle when the selected time period has elapsed and the defrost sensor sees a temperature below freezing. At the start of a defrost cycle, the defrost control will energize the reversing valve solenoid, shifting the reversing valve and de-energizing the outdoor fan. The defrost relay will also close, energizing temporary heat for increased comfort during defrost (if the indoor unit is so equipped). The heat pump will remain in defrost until the defrost sensor has determined that the frost has been removed from the coil or a 10-minute period has elapsed, whichever comes first.

Defrost Thermostat

The defrost thermostat is located on the liquid line between the check/expansion valve and the distributor. When defrost thermostat senses 42ºF or cooler, the thermostat contacts close and send a signal to the defrost control board to start the defrost timing. It also terminates defrost when the liquid line warms up to 70ºF.

Defrost Control

The defrost control board includes the combined functions of the time/temperature defrost control, defrost relay, diagnostic LEDs and terminal strip for field wiring connections. See “Defrost Control Board” in the “Adjust Defrost System” section.

The control provides automatic switching from normal heating operation to defrost mode and back. During compressor cycle (call for defrost), the control accumulates compressor run times at 30, 60 or 90 minute field-adjustable intervals. If the defrost thermostat is closed when the selected compressor run time interval ends, the defrost relay is energized and defrost begins.

Defrost Control Timing Pins

Each timing pin selection provides a different accumulated compressor run time period during one thermostat run cycle. This time period must occur before a defrost cycle is initiated. The defrost interval can be adjusted to 30 (T1), 60 (T2) or 90 (T3) minutes. See “Defrost Control Board” in the “Adjust Defrost System” section. The defrost timing jumper is factory-installed to provide a 60-minute defrost interval. If the timing selector jumper is not in place, the control defaults to a 90-minute defrost interval. The maximum defrost period is 14 minutes and cannot be adjusted.

A test option is provided for troubleshooting. The test mode may be started any time the unit is in the heating mode and the defrost thermostat is closed or jumpered. If the jumper is in the test position at power-up, the control will ignore the test pins. When the jumper is placed across the Test pins for 2 seconds, the control will enter the defrost mode. If the jumper is removed before an additional 5-second period has elapsed (7 seconds total), the unit will remain in defrost mode until the defrost thermostat opens or 14 minutes have passed. If the jumper is not removed until after the additional 5-second period has elapsed, the defrost will terminate and the test option will not function again until the jumper is removed and re-applied.

Compressor Delay

The defrost board has a field-selectable function to reduce occasional sounds that may occur while the heat pump is cycling in and out of the defrost mode. The compressor will be cycled off for 30 seconds while going in and out of the defrost mode when the compressor delay jumper is removed.

NOTE: The 30-second “off” cycle is not functional when jumpering the TEST pins.

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