Lennox International Inc Dave Lennox Signature Collection XP17 System HEAT PUMPS Unit Sensors

UNIT SENSORS

Sensors connect to the heat pump control through a field-replaceable harness assembly that plugs into the control. Through the sensors, the heat pump control detects outdoor ambient and coil temperature fault conditions. As the detected temperature changes, the resistance across the sensor changes. table 13 shows how the resistance varies as the temperature changes for both type of sensors. Sensor resistance values can be checked by ohming across pins shown in table 12.

NOTE , be

aware that a sensor showing a resistance value that is not within the range shown in table 12, 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 need to be replaced.

Ambient Temperature Sensor (RT13)

See table 12 for sensor range. If the ambient sensor is detected as being open, shorted or out of the temperature range of the sensor, the heat pump control will not perform demand defrost operation. The heat pump control will revert to time/temperature defrost operation and will display the appropriate alert code. Heating and cooling operation will be allowed in this fault condition.

Coil Temperature Sensor (RT21)

See table 12 for sensor range. If the defrost coil sensor is open, shorted or out of the temperature range of the sensor, the heat pump control 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.

High Discharge Line Temperature Sensor

This model does not use a high discharge line temperature sensor. The cable assembly attached to the heat pump control’s E30 connection has a 10K resister installed between pins 1 and 2 as illustrated in figure 24. No alerts or alarms would be generated if resistor is damage.

COIL TEMPERATURE
SENSOR
AMBIENT AIR	10K RESISTOR
TEMPERATURE SENSOR

Figure 24. 10k Resistor Location

Table 12. Sensor Temperature / Resistance Range

Sensor	Temperature	Resistance values	Pins/Wire
	Range °F (°C)	range (ohms)	Color
Outdoor			3 and 4
(Ambient)	−40 (−40) to 140		(Black)
		280,000 to 3750
	(60)		5 and 6
Coil
			(Brown)
NOTE Sensor resistance decreases as sensed temperature
increases (see table 13).

W Input Fault or Miswire

In case of a W input fault or possible miswire, the system will function as listed in the sequence of operation in figure 30.

Shift Delay (E37)

The heat pump control 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 (E37), 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.

*30
SECOND DELAY	FACTORY DEFAULT OR WHEN
	JUMPER IS MISSING
	30

0 SECOND DELAY

0

Figure 25. Shift Delay Settings

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XP17 SERIES