Differential Air Pressure Sensor - IBC VFC 15-150 Manual

Control wire plug
Unplug to run fan full speed
Removing circuit board cover
Circuit board revealed
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
35 VdC Positive power
red
terminal
35 VdC negative power
Blue
terminal
Black signal from controller
White Fan tach.
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.
Figure 32 (right): Test
points on circuit board
for air pressure sensor
voltage readings
TROUbLESHOOTING
Fan will only operate at max.
speed if disconnected.
Fan will only operate at max.
speed if disconnected.
Fan will only operate at max.
speed if disconnected.
2 pulses/rev (freq x 30=rpm)
5-3