Hussmann KRACK MK Series, Инструкция по установке и эксплуатации

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MK/MV – Medium Profile Series Unit Coolers (E206993_M) 23
6 AIR DEFROST SEQUENCE OF OPERATION
6.1 SEQUENCE OF OPERATION
1. The unit cooler fan motors are energized, and the fans operate continually.
2. The room thermostat calls for cooling. The liquid solenoid valve opens allowing liquid to flow to the
unit cooler. The suction pressure rises and starts the compressor.
3. When the room temperature is satisfied the thermostat opens and closes the liquid solenoid. The
compressor continues to run until the suction pressure reaches the low-pressure cutout setting and
shuts off the compressor.
4. The fan circulates air over the coil and frost melts.
For air defrost to work properly the compressor run time should not exceed 40 minutes per hour.
Figure 8 AIR DEFROST WIRING 1 PH
Figure 9 AIR DEFROST WIRING 3 PH
7 ELECTRIC DEFROST SEQUENCE OF OPERATION
The electric defrost cycle is time clock initiated and temperature terminated with a timer and or high
temperature over-ride. For systems with multiple unit coolers and a single defrost time clock the
defrost termination thermostat must be wired in series. Reference figures 6, 7, 9, 10, and 11 for electric
defrost wiring diagrams.
7.1 SEQUENCE OF OPERATION
7.1.1 STEP A: NORMAL REFRIGERATION CYCLE
1. Power is supplied to terminals “N’ and “4” on the defrost timer.
2. The heater safety and fan delay thermostat are closed, the defrost termination thermostat is off,
and the defrost heaters are off.
3. The unit cooler fan motors are energized, and the fans operate continually.
4. The systems compressor operates in accordance with the demand of the room thermostat.
5. Frost slowly builds up on the evaporator fins.