Lennox International Inc 4HP18LT manual Defrost Control Timing Pins, Compressor Delay, Time Delay

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. 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 reapplied.

Compressor Delay

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

Time Delay

The timed-off delay is 5 minutes long. The delay helps to protect the compressor from short cycling in case the power to the unit is interrupted or a pressure switch opens. The delay is bypassed by placing the timer select jumper across the TEST pins for 0.5 seconds.

Pressure Switch Circuit

The defrost control includes two pressure switch circuits. A high pressure switch is connected to the board’s HI-PS terminals(See Figure 14). The low pressure, or loss-of- charge pressure, switch is connected to the LPS terminals.

During a single demand cycle, the defrost control will lock out the unit after the fifth time that the circuit is interrupted by an pressure switch wired to the control board. In addition, the diagnostic LEDs will indicate a locked-out pressure switch after the fifth occurrence of an open pressure switch (See Table 9). The unit will remain

locked out until power to the board is interrupted, then re- established, or until the jumper is applied to the TEST pins for 0.5 seconds.

NOTE: The defrost control board ignores input from the low pressure switch terminals as follows:

•During the TEST mode

•During the defrost cycle

•During the 90 seconds start-up period

•For the first 90 seconds each time the reversing valve switches heat/cool modes

If the TEST pins are jumpered and the 5 minute delay is being bypassed, the LO-PS terminal signal is not ignored during the 90-second start-up period.

Diagnostic LEDs

The defrost board uses two LEDs for diagnostics. The LEDs flash a specific sequence according to the condition as shown in Table 9.

Defrost Control Board

Diagnostic LEDs

Table 9

506470-01 Issue 1007 Page 19