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www.manitowocfsusa.com 800-225-9916 19
Air Defrost:
Instructions for setting the timer is located on the inside cover of the time clock. The defrost
timer clock must be set to the correct time at initial start-up and after any power interruptions.
Set the clock by rotating the clock face until the correct time is at the arrow on the face of the
timer. The switch is programmed by pushing the captive trippers to the outer ring for the entire
period the load is to be turned “ON”. When the tripper is pushed to the inside, the switch is in
the “Defrost” position. Each defrost tripper represents 15 minutes of defrost time. The timer is
factory set for four defrost cycles daily at the following times: 4:00AM, 10:00AM, 4:00PM, and
10:00PM. Each defrost cycle is programmed for 30 minutes duration. The defrost times may
be changed to initiate at periods of low activity (trippers pushed out will close contacts to
terminals 3 & 4).
Note: The timer starts the defrost cycle automatically at the predetermined times. A setting of
two to four defrost cycles per day is typical. For heavier frost loads, additional cycles may be
required.
When the defrost cycle begins:
1. Switch 3 to 4 opens in the time clock, breaking the circuit to the temperature control and
liquid line solenoid valve. This allows the compressor to pump down and shut off. Note,
the evaporator fans continue to run during the defrost cycle.
2. At the end of the defrost duration, switch contacts 3 and 4 close, energizing the
temperature control, solenoid valve circuit.
3. The suction pressure rises. When the cut-in pressure setting of the low pressure control
is reached, the compressor contactor is energized, and the compressor starts.
4. The system operates in the refrigeration cycle until the next defrost cycle is initiated by
the timer.
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