SECOND−STAGE Operation

High Pressure Switch (S4)

When the high pressure switch trips, the demand defrost control will cycle off the compressor, and the strike counter in the demand defrost control will count one strike. High Pressure (auto reset) − trip at 590 psig, reset at 418.

Low Pressure Switch (S87)

When the low pressure switch trips, the demand defrost control will cycle off the compressor, and the strike counter in the demand defrost control will count one strike. Low pressure switch (auto reset) − trip at 25 psig, reset at 40 psig.

The low pressure switch is ignored under the following conditions:

SDuring the defrost cycle and 90 seconds after the termination of defrost

SWhen the average ambient sensor temperature is below 15° F (−9°C)

SFor 90 seconds following the start up of the compressor

SDuring test mode

Ambient Sensor (RT13)

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 demand defrost control will not perform demand defrost operation. The demand defrost control 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.

Coil Sensor (RT21)

Coil Sensor

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 demand defrost 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 Temperature Sensor (RT28)

If the discharge line temperature exceeds a temperature of 285°F (140°C) during compressor operation, the demand defrost control will de−energize the compressor contactor output (and the defrost output, if active). The compressor will remain off until the discharge temperature has dropped below 225°F (107°C) and the 5-minute anti−short cycle delay has been satisfied. This sensor has two fault and lockout codes:

1.If the demand defrost control recognizes five high discharge line temperature faults during a single (Y1) compressor demand, it reverts to a lockout mode and displays the appropriate code. This code detects shorted sensor or high discharge temperatures. Code on demand defrost control is Discharge Line Temperature Fault and Lockout.

2.If the demand defrost control recognizes five temperature sensor range faults during a single (Y1) compressor demand, it reverts to a lockout mode and displays the appropriate code. The demand defrost control detects open sensor or out-of-temperature sensor range. This fault is detected by allowing the unit to run for 90 seconds before checking sensor resistance. If the sensor resistance is not within range after 90 seconds, the demand defrost control will count one fault. After five faults, the demand defrost control will lockout. Code on demand defrost control is Discharge Sensor Fault and Lockout.

The discharge line sensor, which covers a range of 150°F (65°C) to 350°F (176°C), is designed to mount on a ½" refrigerant discharge line.

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

Crankcase Heater (HR1) and Crankcase Thermostat

Switch (S40)

The reference models are equipped with a 70 watt, belly band type crankcase heater. HR1 prevents liquid from accumulating in the compressor. HR1 is controlled by a thermostat located on the liquid line. When liquid line temperature drops below 50° F the thermostat closes energizing HR1. The thermostat will open, de−energizing HR1 once liquid line temperature reaches 70° F .

Liquid Line Bi−Flow Filter Drier

The unit is equipped with a large−capacity biflow filter drier which keeps the system clean and dry. If replacement is necessary, order another of like design and capacity. The replacement filter drier must be suitable for use with HFC−410A refrigerant.

The replacement filter drier must be suitable for use with HFC−410A refrigerant.

If the demand defrost control (A108) receives a call for second−stage compressor operation Y2 in heating or cooling mode and the first-stage compressor output is active, the second-stage compressor solenoid output will be energized.

If first-stage compressor output is active in heating mode and the outdoor ambient temperature is below the selected compressor lock−in temperature, the second-stage compressor solenoid output will be energized without the Y2 input. If the jumper is not connected to one of the temperature selection pins on P3 (40, 45, 50, 55°F), the default lock−in temperature of 40°F (4.5°C) will be used.

The demand defrost control de−energizes the second-stage compressor solenoid output immediately when the Y2 signal is removed or the outdoor ambient temperature is 5°F above the selected compressor lock−in temperature, or the first-stage compressor output is de−energized for any reason.

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XP16 SERIES