Lennox International Inc PWGI8E7.2, PWC24E9.2, PWC302 Defrost Control, Heating, Defrost Cycle

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mum. Run the 208 or 230 volt, 60 hertz electric power supply through a fused disconnect switch to the control box of the unit and connect as shown in the wiring dia- gram located on the inside of the control access panel.

The unit must be electrically grounded in accordance with local codes or, in the absence of local codes, with the National Electrical Code ANSI/NFPA No. 70 (latest edition) or CSA C22.2 Part 1 (latest edition).

Power supply to the unit must be NEC Class 1 and must comply with all applicable codes. A fused disconnect switch should be field provided for the unit. The switch must be separate from all other circuits. If any of the wire supplied with the unit must be replaced, replacement wire must be of the type shown on the wiring diagram.

Electrical wiring must be sized to minimum circuit ampacity marked on the unit. Use copper conductors only. Each unit must be wired with a separate branch circuit and be properly fused.

OPERATION

Sequence of Operation

Cooling

When the thermostat is in the cooling mode, the O circuit is powered which energizes the reversing valve. Upon cooling demand, the thermostat closes circuit R toY and

G.Closing R to Y closes the unit contactor, starting the compressor and outdoor fan. The thermostat automati- cally closes R to G circuit which also brings on the indoor blower at the same time. Upon satisfying cooling demand, the thermostat will open the above circuits and open the main contactor, stopping the compressor and outdoor fan. If the unit is equipped with a time delay, the blower will continue to operate for 90 seconds which improves

system efficiency.

Heating

Upon heating demand, the thermostat closes circuit R to Y, which closes the unit contactor, starting the compressor and outdoor fan. The reversing valve is not energized in the heating mode. -Thethermostat again automatically brings on the indoor fan at the same time. The second stage of the thermostat closes circuit R to W, which closes the unit sequencers, bringing the auxiliary electric heat on. Upon satisfying heating demand, the thermostat opens the above circuits and stops unit operation.

Defrost Cycle

If the outdoor ambient conditions are such that frost forms on the outdoor coil, the defrost control monitors the need for and initiates and terminates defrost cycles as neces- sary to maintain system performance. The defrost control

is time/temperature initiated and temperature terminated with a maximum defrost time (time-out) of 10 minutes.

Time between defrost cycles is preset at 60ominute intervals at the factory, but can be field adjusted between 30, 60 or 90 minutes. To field adjust time between defrost

cycles, place defrost time plug in the proper position (see Figure 3). For best performance in Region IV, the

PWC243 defrost interval should be adjusted to 30 min- utes.

Defrost control will initiate a defrost cycle if the time period has elapsed and the defrost sensor sees a temperature below freezing. At the start of a defrost cycle, the defrost control will energize the reversing valve solenoid, shifting the reversing valve and de-energizing the outdoor fan. The defrost relay will also close, energizing auxiliary heat for increased comfort during defrost. The unit will remain in defrost mode until the defrost sensor has determined that the frost has been removed from the coil or a 10- minute time period has elapsed.

The defrost control is also equipped with a setof pins to aid in troubleshooting of the defrost system (see Figure 3). The following is a brief outline of the testing of the defrost system.

. Defrost sensor must be closed, 32°F or below. If temperatures are such that switch will not close, jumper between defrost sensor terminals on the defrost control,

2.Start system in heating operation.

. Jumper test pins, A 1/4" quick connect terminal crimped onto a solid wire or brazing rod works well for test jumper. Closing test pins speeds up time interval by a factor of 256.

Defrost Control

Defrost

TestPins.,,,=i

Defro=/

TimePlug

Defrost Control Setting		Defrost Test Cycle Time
30	minutes	7 seconds
60	minutes	14 seconds
90	minutes	21 seconds

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