DISPLAY CABINET HEATED
12
P/N 1010772 Rev. D 12/13
MAINTENANCE (continued)
Technical Theory of Operation
When the Rocker Switch (power On/Off) is set to ON,
line voltage flows to the primary side of the Step Down
Transformer. The Transformer’s secondary side sup-
plies 12-14 VAC to terminals T1 and T2 on the Control
Board.
Once powered, and provided that the Cabinet tem-
perature is below the setpoint temperature, the Control
Board, in conjunction with a 100K ohm Thermistor, calls
for heat by supplying 15-20 VDC to terminals 3 (+) and
4 (-) on the Solid State Relay. Once powered, the Solid
State relay closes terminals 1 and 2, which allows line
voltage to flow to the heater(s).
As the Cabinet Temperature begins to increase, the
Thermistor monitors the Cabinet Temperature and
its ohms begin to decrease. Once the Cabinet tem-
perature approaches the setpoint temperature, the
Thermistor’s ohms are relayed over to the Control
Board.
The Control Board receives the ohms and proceeds to
remove the 15 - 20 VDC to the Solid State Relay since
the Heating Circuit has now become satisfied. The
relay terminals 1 and 2 open and the heater(s) stop
heating. The heating circuit will cycle on and off as
needed. The control board has the ability to display
several codes (see the section titled
Display Codes
in
the Maintenance section of this manual).
On some models, the Heated air is circulated by one
or two blower motors, while other models do not use
blower motors. Some models use water trays while
other models use a crumb tray.
NOTE: Crumb Trays (Figure 1) must NOT contain
water.
When the Water Trays (Figure 1) are filled with water,
the heat radiated by the heaters cause the water
to evaporate, which gradually adds humidity to the
Cabinet (see the Operation section of this manual).
NOTE: Water Trays use a diffuser (Figure 1). The
purpose of a diffuser is to shield away excessive
heat. This will allow the water to evaporate at a
slower rate resulting in a reduction of humidity in
the cabinet. On 120 volt units, the front display
panel is illuminated by 4, 6, or 8 120V, 10 watt, can-
descent bulbs that are wired in parallel (see the
Wiring Diagram section of this manual for 120 Volt
units).
NOTE: The 220/240 volt units also use the 120 volt
bulbs, but the bulbs are wired in series and in two
bulb circuits (see the Wiring Diagram section of this
manual for 220/240 volt units).
The internal cabinet area is illuminated by 1 or 2 120
volt, 100 watt halogen bulb(s). On 120 volt units, each
halogen bulb is wired in series with a 10 ohm, 50 watt
resistor (see the Wiring Diagram section of this manual
for 120 volt units). The purpose of the resistors is to
allow for a voltage drop. The voltage drop allows the
halogen bulb’s brightness to be slightly reduced.
NOTE: On 220/240 units, the Halogen Bulbs and
Resistors are all wired in series with one another.
See the Wiring Diagram for 220/240 volt units.
