Convection Fan; Convection Fan Operation - Viking VDSC548T Series Service Manual

Service Diagnostics and Procedures
This unit utilizes capacitors for the different speeds. They should be discharged before handling to avoid
electric shock.
Control Board Diagnosis

Convection Fan

Locate the P4 connector and line break relay.
The P4 connector will have a Molex plug containing
four wires:
(1) blue/black wire - Fwd motor winding and
Hi speed capacitor
(2) yellow/white wire - Rev motor winding
(3) orange/white wire- Lo speed capacitor
(4) orange/black wire - Hi speed capacitor
Convection Operation
The convection system consists of a two-speed,
two-direction fan motor. The main power, speed,
and direction are controlled by the EOC by three
relays (K5, K6, and K7). K5 is the main control
(power) relay and is an SPDT relay. It controls all
functions of the convection fan system. The photo
below shows the K5 relay energized.
Clockwise (FWD)–Low Speed
K5
When closed, it sends power to the common
terminal of the K6 relay (direction) and is an
SPDT relay.
The output from K5 is connected to the C (common
terminal) of K6. When it is not energized (as shown
above), power flows through the C terminal,
through the N.C. contact and out the FWD
contact on the board.
© 2011 Viking Preferred Service
K6 K7
WARNING
K7 is the speed relay and is also an SPDT relay.
When not energized, the LO circuit is energized
through C terminal of the K7 relay. This will cause
both capacitors to be in series causing the fan to
run at a reduced speed. The photo below shows
the K7 energized. The N.O. terminal is now closed
causing a bypass of one of the 2 capacitors. With
only one capacitor in series, the unit will run at a
higher speed.
Clockwise (FWD)–High Speed
The photo below shows the K6 relay energized
which will cause the motor to rotate in a REV
(counterclockwise) direction. K7 is not closed, so
the speed is LOW.
Counterclockwise (REV)–Low Speed
K5 K6 K7
K5 K6 K7
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