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Diagnosing the V/S Vent Motor with the V/S Troubleshooter
7. Turn the Variable Speed Troubleshooter switch to
the HIGH position quickly. Too long a delay at the
"OFF" position will cause the motor to stop. Does
the Variable Speed Vent Motor go to high speed
operation?
YES:
No fault with Variable Speed Vent Motor
or the high pressure switch HPS/PS2. If
the furnace will not cycle the Vent Motor,
replace the IFC control.
NO:
Unhook the brown wire from the high
pressure switch HPS/PS2 and check motor
again for high speed operation. If motor
RPM now goes up, the high pressure
switch HPS was closed. Repair as needed
or replace the high pressure switch
HPS/PS2. If the motor will not go to high
speed and high pressure switch HPS/PS2
is OK, replace the Variable Speed Motor.
8A.Is there 10 – 13 VDC between pins #2 and #3 at
the troubleshooter plug?
YES:
Go to Step #8B.
NO:
Unplug the Variable Speed Vent Motor
from the Troubleshooter. Check for voltage
between pins #2 and #3 again. The voltage
should read between 10 – 16 VDC. If volt-
age is not present but goes low or to zero
VDC when the Variable Speed Vent Motor
is again plugged into the Troubleshooter,
replace the Variable Speed Vent Motor.
If the correct D.C. voltage is not present
when the Variable Speed Vent Motor is
unplugged from the Troubleshooter, check
for the 24 VAC to it. If the 24 VAC is present
at the Troubleshooter but no D.C. voltage
is present, repair or replace the Trouble-
shooter.
8B. Is there 120 VAC line voltage present between
pin #11 white wire and pin #12 black wire at the
Variable Speed Vent Motor plug?
YES:
Check the Variable Speed Vent Motor
red jumper wire connecting pin #6 and
pin #10 together. If a fault is found with
this jumper, repair or replace as needed
and re-check the Variable Speed Vent
Motor, if the red jumper is OK and the
correct voltage was read during checks 8A
and 8B. If the Variable Speed Vent Motor
will not run, replace it.
NO:
Check for 120 VAC at the IFC terminals
which supply power to the Variable Speed
Vent Motor. If the line voltage is present,
check the Variable Speed Vent Motor hous-
ing limit switch and the furnace wiring.
9. Remove the orange wire from the low pressure
switch LPS/PS1. Will the Variable Speed Vent
Motor now start on low speed?
YES:
Fault is with the low pressure switch
LPS/PS1. This switch is normally open
and it is closed. Repair or replace switch
as needed.
NO:
Go back to Step #8A.
37
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