TK 54343-18-MM-EN
53
Defrost Mode – SPECTRUM Multi-Temp Units
Defrost can be initiated in a compartment any time its evaporator coil temperature is below 36 F (2.2 C), causing the
defrost termination switch to close. Defrost is initiated automatically by the defrost timer, or manually using the In-Cab
Control Box.
Defrost will continue until the evaporator coil temperature rises to 48 F (8.9 C) causing the defrost termination switch to
open or the defrost termination timer has expired (whichever occurs first), ending the defrost cycle. Defrost cycle can be
also terminated by pressing the On/Off Key to turn the unit off, and then pressing it again to turn the unit back on.
Defrost in one compartment turns all evaporator fans off. Effectively delaying cool in the other compartment.
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High pressure refrigerant vapor leaves the compressor and flows through the oil separator where oil is separated and
returned to the suction tube. Most of the refrigerant flows into the hot gas line. An insignificant amount flows through
the condenser, receiver, drier, and liquid indicator into the liquid lines.
The Zone 1 hot gas solenoid is open so the refrigerant flows through the hot gas line and drain pan heater to the Zone 1
evaporator. There, the refrigerant heats the evaporator. The refrigerant returns to the compressor through the CPR
check valve and suction lines.
The Zone 2 liquid line solenoid is open but the pressure in the suction lines from the Zone 1 evaporator is high enough
to keep refrigerant from flowing through the Zone 2 evaporator.
• Zone 1 Liquid Line Solenoid – Closed/De-energized
• Zone 1 Hot Gas Solenoid – Open/Energized
• Zone 2 Liquid Line Solenoid – Open/Energized
• Zone 2 Hot Gas Solenoid – Closed/De-energized
• CPR Bypass Solenoid – Open/De-energized
• Liquid Injection Solenoid – Closed/De-energized, but will open (energize) if the liquid injection switch closes.
Figure 22. SPECTRUM Model 10 Zone 1 Defrost, Zone 2 Delayed Cool
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