Control Compressor, Condenser Fan, Dual Refrigerant Valve and Evaporator Fan Motors
The control senses evaporator and compartment temperatures via thermistors; one on each evaporator, and one in
each compartment. High Offset (Cut-in) is governed by the evaporator temperatures. Low Offset (Cut-out) is gov-
erned by the compartment temperatures. High Offset and Low Offset are based on the set-point.
If either evaporator calls for cooling (evaporator temperature at high offset), power is supplied to the compressor and
condenser fan motor, cycling them ON. The corresponding evaporator fan relay supplies power to the appropriate
evaporator fan switch, cycling the fan on. Then, two relays on the control board are used to control the dual refriger-
ant valve. The relays are in series with one another. The first “pulse” relay controls the length of time the solenoid
is energized (500ms / 30 pulses per 1/2 second). The second “sign” relay controls the negative polarity, or positive
polarity of the pulse supplied to the valve’s solenoid (determined by which evaporator is calling for cooling, ( + ) =
Upper Evaporator, ( - ) = Lower Evaporator). So, when an evaporator calls for cooling, the bead inside of the T-con-
nection of the refrigerant valve is forced to one side or the other, depending on the polarity of the pulse, supplying
refrigerant to the appropriate evaporator (See Figure 3-17).
NOTE: If neither compartment is calling for cooling, the compressor and condenser fan are switched off.
NOTE: Evaporator fans are switched off when the door is open and disabled if the unit is in Showroom Mode.
NOTE: When in Sabbath Mode, evaporator thermistors still control energizing of the compressor and evaporator
fans, except
there is a ran-
dom fifteen
(15) to twenty-
five (25) sec-
ond delay
before power
is supplied to
components.
Wine Storage
Wine Storage
(400-
(400-
2
2
)
)
Series
Series
Electronic Control System
3-11
#3758410 - Revision C - May, 2014
Figure 3-17. Cooling Signal Trace (Upper Evaporator at High-Offset Temperature, Calling for Cooling)
N.O.
N.O.
N.C.
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