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3.2.5 Defrost system
A defrost cycle can be started by pressing the manual
defrost switch or automatically by the defrost timer,
when the unit is in cool mode and below 35°F.
The defrost cycle operates by energizing the defrost
relay. The defrost relay energizes the defrost solenoid
valve (and the condenser solenoid valve on units
equipped with the heat option). The defrost relay also
interrupts power to the evaporator and condenser
fans, which stops the evaporator and condenser fans.
Energizing the defrost solenoid valve diverts hot gas
into the evaporator coil, melting ice.
To check the defrost cycle, run the unit on Cool to
drop the evaporator coil to a temperature below 35°
F.
Press the manual defrost switch. The unit should shift
from Cool to Defrost Mode. If the unit continues to
Cool, double check the evaporator coil temperature.
3.2.6 Manual defrost
A manual defrost button is in the In-Cab control box.
Pressing the manual defrost switch initiates the
defrost cycle if the unit is in cool mode.
3.2.7 Defrost relay
The defrost relay controls operation of the defrost
cycle. When the defrost timer completes the circuit,
the defrost relay is energized. This energizes the
defrost solenoid valve (wire 26) and de-energizes the
fan relay.
The defrost relay stays energized until the defrost
cycle is terminated or the ON-OFF Key is pressed.
3.2.8 Defrost solenoid valve (Hot Gas Solenoid
Valve)
The defrost solenoid valve is an electrical valve that
controls the flow of refrigerant through the
refrigeration system.
The defrost solenoid valve is energized by the pin
26. When the defrost solenoid valve is energized it routes
hot refrigerant gas to the evaporator.
3.2.9 Condenser Inlet valve
This valve is normally open. When open it allows
refrigerant to move through the condenser to complete to
cooling circuit. In heat or defrost the solenoid coil is
activated. Closing the valve. Bypassing the condenser
allow the hot gas to enter the evaporator section.
Figure 8 - Solenoid Valve
