Defrost System
The defrost system is both adaptive and preemptive.
The adaptive portion of the system adjusts the run time between defrost cycles to provide the optimum
defrost duration.
Preemptive defrost will attempt to prevent defrost cycles from occurring during high-use periods.
The Main Control board monitors door openings to track high usage periods. If the system identifies
that a defrost cycle is likely to occur during a high use period, it will either begin defrost early or delay
defrost until after the high use period.
Before initiating a defrost cycle, the system will operate at maximum cooling capacity for 30 minutes.
This will sub-cool the freezer section and result in a freezer temperature up to ten degrees below
normal. This additional cooling will help to prevent the interior temperatures from rising much beyond
the setpoint temperature during defrost.
There are three heaters wired in parallel for the defrost system. The glass defrost heaters are attached
to the evaporator coil, the foil drip pan heater is under the drip tray and the tube heater is around the
drain tube to prevent freeze-ups leading out of the evaporator section. Defrost termination is provided
by the evaporator thermistor readings. There is a mechanical defrost thermostat wired is series with
the heaters to act as a safety thermostat should the Main Control board fail to open the defrost circuit.
The defrost water is routed from the evaporator area to the machine compartment through the divider
wall. The water flows into an evaporation tray with wicking pads to accelerate evaporation. These
pads are located in the airpath after the condenser and the compressor so that warmed air can aid in
evaporation.
Page 2-11
s
eCTion
2 - T
eChniCal
o
rienTaTion
Defrost Heater Locations
NOTE
The defrost system can be energized through the Service Tests mode. Service Test 11 will
energize the defrost heaters so long as the defrost terminator is closed. The defrost system will
draw approximately 3 amps.
While in Service Test 11 the display will show the evaporator temperature. A rising evaporator
temperature will confirm that the defrost heater is energized without the need to access the
evaporator.
The defrost heaters are accessed in the same manner as the evaporator coil.
•
•
•