Defrost Temperature Termination Shunt (Jumper) Pins—The defrost board selections are: 50, 70, 90, and 100°F (10, 21, 32 and 38°C). The shunt termination pin is factory set at 50°F (10°C). If the temperature shunt is not installed, the default termination temperature is 90°F (32°C).
DELAY MODE
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. When a jumper is installed on the DELAY pins, the compressor will be cycled off for 30 seconds going in and out of the defrost mode. Units are shipped with jumper installed on DELAY pins.
NOTE - The 30 second off cycle is NOT functional when jumpering the TEST pins.
OPERATIONAL DESCRIPTION
The defrost control board has three basic operational modes: normal, calibration, and defrost.
Normal Mode—The demand defrost board monitors the O line, to determine the system operating mode (heat/ cool), outdoor ambient temperature, coil temperature (outdoor coil) and compressor run time to determine when a defrost cycle is required.
Calibration Mode—The board is considered uncalibrated when power is applied to the board, after cool mode operation, or if the coil temperature exceeds the termination temperature when it is in heat mode.
Calibration of the board occurs after a defrost cycle to ensure that there is no ice on the coil. During calibration, the temperature of both the coil and the ambient sensor are measured to establish the temperature differential which is required to allow a defrost cycle.
Defrost Mode—The following paragraphs provide a detailed description of the defrost system operation.
DETAILED DEFROST SYSTEM OPERATION Defrost Cycles—The demand defrost control board initiates a defrost cycle based on either frost detection or time.
!Frost Detection—If the compressor runs longer than 30 minutes and the actual difference between the clear coil and frosted coil temperatures exceeds the maximum difference allowed by the control, a defrost cycle will be initiated.
IMPORTANT - The demand defrost control board will allow a greater accumulation of frost and will initiate fewer defrost cycles than a time/ temperature defrost system.
!Time—If 6 hours of heating mode compressor run time has elapsed since the last defrost cycle while the coil temperature remains below 35°F (2°C), the demand defrost control will initiate a defrost cycle.
Actuation—When the reversing valve is de-energized, the Y1 circuit is energized, and the coil temperature is below 35°F (2°C), the board logs the compressor run time. If the board is not calibrated, a defrost cycle will be initiated after 30 minutes of heating mode compressor run time. The control will attempt to self-calibrate after this (and all other) defrost cycle(s).
Calibration success depends on stable system temperatures during the 20-minute calibration period. If the board fails to calibrate, another defrost cycle will be initiated after 45 minutes of heating mode compressor run time. Once the defrost board is calibrated, it initiates a demand def rost cycle when the difference between the clear coil and frosted coil temperatures exceeds the maximum difference allowed by the control OR after 6 hours of heating mode compressor run time has been logged since the last defrost cycle.
NOTE - If ambient or coil fault is detected, the board will not execute the “TEST” mode.
Termination—The defrost cycle ends when the coil temperature exceeds the termination temperature or after 14 minutes of defrost operation. If the defrost is terminated by the 14-minute timer, another defrost cycle will be initiated after 30 minutes of run time.
Test Mode—When Y1 is energized and 24V power is being applied to the board, a test cycle can be initiated by placing the termination temperature jumper across the “Test” pins for 2 to 5 seconds. If the jumper remains across the “Test” pins longer than 5 seconds, the control will ignore the test pins and revert to normal operation. The jumper will initiate one cycle per test.
Enter the “TEST” mode by placing a shunt (jumper) across the “TEST” pins on the board after power-up. (The “TEST” pins are ignored and the test function is locked out if the shunt is applied on the “TEST” pins before power-up). Board timings are reduced, the low- pressure switch is ignored and the board will clear any active lockout condition.
Each test pin shorting will result in one test event. For each “TEST” the shunt (jumper) must be removed for at least 1 second and reapplied. Refer to flow chart for “TEST” operation.
Note: The Y1 input must be active (ON) and the “O” room thermostat terminal into board must be inactive.
DEFROST BOARD DIAGNOSTICS
See defrost control board diagnostic LED table on next page to determine defrost board operational conditions and to diagnose cause and solution to problems.
