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4.19
Low Ambient Heater
In low ambient temperatures, a 12 Volt, 7 Watt low power heater is used to keep the temperature in the
Provision compartment above freezing. The ambient heater is controlled by the power/control module,
which uses pulse width modulation (PWM) to run the heater at 58% to give 4.1 watts of heat. The ambient
heater is situated in the air duct of the "T" models and in the divider partition on "B" models. The element
has the purpose of warming the area if the ambient becomes too low, hence in the "B" models the element is
on when the compressor cycles off as the crispers could freeze.
operates when the percentage of compressor run time for the last four cycles drops below 30%. It switches
off when the percentage run time increases to above 35%. The heater will always be switched off during
defrosting. There may be less than 4 cycles in the calculation if a defrost has occurred or there were long
cycle times.
4.20
PC / FC Fans
4.20.1
"B" Model Fan
There are two 12 Volt DC electrically commutated motors (ECMs). They provide the required cooling air
flow to both compartments.
technique. The power/control module controls the on/off of the compressor, and the fans. The speed of the
FC fan is set, and the speed of the PC fan is regulated using pulse width modulation.
The freezer compartment fan will always be set at the maximum FC fan speed, with the PC fan being
adjusted to meet the requirement of that compartment. We alter the speed of the FC fan under certain
loading conditions. Therefore the PC fan speed will be set at the average speed used from the previous
cycles under normal door openings and loading conditions.
When the compressor is turned on, provided the doors are closed both the fans will also be switched on
except immediately following a defrost cycle, where there is a delay of 5 minutes after the compressor has
started before the FC fan starts.
"T" MODEL
Diagram 4.19
The motor speeds are controlled using a pulse width modulating (PWM)
The low ambient heater in "T" models
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