5-3
TROUBLESHOOTING
VFC 15-150 - VFC 45-225 MODULATING GAS BOILERS
5.2.2 Fan/blower
operating power is provided by means of a separate 120 VaC connector at
the back of the fan (white/black/green). Control of the fan is provided via a four
lead connector at the front of the fan. this connector feeds a PWM control
signal (black wire) from the controller and provides a tachometer signal (white
wire) back from the fan. unplugging the connector will cause the fan to go to
high speed and trigger a “Blocked Vent error” within 6 seconds if the boiler is
operating.
LEAD COLOR
FUNCTION
TROUbLESHOOTING
red
35 VdC Positive power
terminal
Fan will only operate at max.
speed if disconnected.
Blue
35 VdC negative power
terminal
Fan will only operate at max.
speed if disconnected.
Black
signal from controller
Fan will only operate at max.
speed if disconnected.
White
Fan tach.
2 pulses/rev (freq x 30=rpm)
Table 9: Fan Operation
5.2.3 Differential Air Pressure Sensor
go to the
Advanced Diagnostics
screen, and with the fan off (
“Fan Duty Cycle
=
0) look for a
Fan Pressure
reading of 102 +/-5. next check with fan in operation,
and look for an increased
Fan Pressure
value. in normal operation, the
Fan
Pressure
reading should move toward the
Required Pressure
value. a backward
movement in
Fan Pressure
indicates the clear vinyl reference lines have been
reversed.
Control wire plug
Unplug to run fan full speed
Circuit board revealed
Removing circuit board cover
Figure 32 (right): Test
points on circuit board
for air pressure sensor
voltage readings
Summary of Contents for VFC 15-150
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