Allied Air Enterprises 4HP16LT manual Defrost Board Pressure Switch Connections

DEFROST BOARD PRESSURE SWITCH

CONNECTIONS

The unit’s automatic reset pressure switches (LO PS - S87 and HI PS - S4) are factory-wired into the defrost board on the LO-PS and HI-PS terminals, respectively.

(OPTIONAL) Low Pressure Switch (LO-PS) — When the low pressure switch trips, the defrost board will cycle off the compressor, and the strike counter in the board will count one strike. The low pressure switch is ignored under the following conditions:

!during the defrost cycle and 90 seconds after the termination of defrost

!when the average ambient sensor temperature is below 15° F (-9°C)

!for 90 seconds following the start up of the compressor

!during “test” mode

High Pressure Switch (HI-PS) — When the high pressure switch trips, the defrost board will cycle off the compressor, and the strike counter in the board will count one strike.

DEFROST BOARD PRESSURE SWITCH SETTINGS High Pressure (auto reset) - trip at 590 psig; reset at 418.

Low Pressure (auto reset) - trip at 25 psig; reset at 40.

5-STRIKE LOCKOUT FEATURE

The internal control logic of the board counts the pressure switch trips only while the Y1 (Input) line is active. If a pressure switch opens and closes four times during a Y1 (Input), the control logic will reset the pressure switch trip counter to zero at the end of the Y1 (Input). If the pressure switch opens for a fifth time during the current Y1 (Input), the control will enter a lockout condition.

The 5-strike pressure switch lockout condition can be reset by cycling OFF the 24-volt power to the control board or by shorting the TEST pins between 1 and 2 seconds. All timer functions (run times) will also be reset.

If a pressure switch opens while the Y1 Out line is engaged, a 5-minute short cycle will occur after the switch closes.

DEFROST SYSTEM SENSORS

Sensors connect to the defrost board through a field– replaceable harness assembly that plugs into the board. Through the sensors, the board detects outdoor ambient, coil, and discharge temperature fault conditions. As the detected temperature changes, the resistance across the sensor changes. Sensor resistance values can be checked by ohming across pins .

Sensor Temp. / Resistance Range

Sensor	Temperature	Red Led (DS1)	Pins/Wire
	Range °F (°C)		Color
Outdoor	-35 (-37 to 120	280,000 to 3750	3 & 4
(Ambient)	(48)		(Black)
Coil	-35 (-37) to 120	280,000 to 3750	5 & 6
	(48)		(Brown)
Discharge (If	24 (-4) to 350	41,000 to 103	1 & 2
applicable)	(176)		(Yellow)

Note: Sensor resistance decreases as sensed temperature increases.

NOTE - When checking the ohms across a sensor, be aware that a sensor showing a resistance value that is not within the range shown, may be performing as designed. However, if a shorted or open circuit is detected, then the sensor may be faulty and the sensor harness will needs to be replaced.

Coil Sensor—The coil temperature sensor considers outdoor temperatures below -35°F (-37°C) or above 120°F (48°C) as a fault. If the coil temperature sensor is detected as being open, shorted or out of the temperature range of the sensor, the board will not perform demand or time/temperature defrost operation and will display the appropriate fault code. Heating and cooling operation will be allowed in this fault condition.

Ambient Sensor—The ambient sensor considers outdoor temperatures below -35°F (-37°C) or above 120°F (48°C) as a fault. If the ambient sensor is detected as being open, shorted or out of the temperature range of the sensor, the board will not perform demand defrost operation. The board will revert to time/temperature defrost operation and will display the appropriate fault code. Heating and cooling operation will be allowed in this fault condition.

NOTE - Within a single room thermostat demand, if 5-strikes occur, the board will lockout the unit. Defrost board 24 volt power “R” must be cycled “OFF” or the “TEST” pins on board must be shorted between 1 to 2 seconds to reset the board.

506468-01 Issue 1004 Page 18