SERVICING
32
2. Remove the thermostat low voltage wires at the furnace
integrated control module terminals.
With Power On (and Door Interlock Switch closed):
I W PR
3. Use a voltmeter, check voltage across terminals R and
C. Must read 24 VAC.
4. No voltage indicates faulty transformer, open fuse, bad
wiring, bad splice, or open door interlock switch.
5. Check transformer primary voltage at incoming line
voltage connections, fuse, splices, and blower door in-
terlock switch.
6. If line voltage is available to the primary side of trans-
former and not at secondary side, the transformer is
inoperative. Replace.
7. After completing check and/or replacement of trans-
former and check and/or repair of control circuit, rein-
stall blower compartment door.
8. Turn on electrical power and verify proper unit opera-
tion.
I
W PR
I
D
I
PWRRRIIR
IIII
IPPWRR
PR
IRDPRPR
DPRIJRRD
D
I
PWR RRII
1. Remove blower compartment door to gain access to the
circulator blower motor and integrated ignition control.
2. Check for any obstruction that would keep the fan wheel
/ fan motor from turning.
3. Check wiring, the motor has two wiring harnesses, a main
harness and a control harness. The main pin harness has:
White neutral wire connected to the Neutral terminal on
the control board.
Black wire connected to the CIRC H terminal on the control
board.
Red wire connected to the COM terminal, which is a
female spade connection next to the T1 – T5 wires on
the control board.
Green ground wire connected to cabinet ground
The control harness has:
The nine speed ECM motor requires a line voltage power
supply (black connected to CIRC H and white connected
to neutral on the control board) as well as a signal on one
of the speed taps (T1-T5).
The speed tap voltage is 3-15 D.C. and can vary
depending speed selection. The voltage reading from any
one of the speed taps is referenced between the female
COM terminal of the motor speed tap harness.
The maximum and minimum allowable external static
pressures are found in the specication section. These tables
also show the amount of air being delivered at a given static
by a given motor speed or pulley adjustment.
The furnace motor cannot deliver proper air quantities (CFM)
against statics other than those listed.
Too great of an external static pressure will result in insucient
air that can cause excessive temperature rise, resulting in
limit tripping, etc. Whereas not enough static may result in
motor overloading.
To determine proper air movement, proceed as follows:
1. With clean lters in the furnace, use a manometer to
measure the static pressure of the return duct at the inlet
of the furnace. (Negative Pressure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. Add the two (2) readings together for total external static
pressure.
Both readings may be taken simultaneously and read
directly on the manometer if so desired. If an air conditioner
coil or Electronic Air Cleaner is used in conjunction with the
furnace, the readings must also include theses components,
as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the minimum
or maximum allowable statics, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
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