SERVICING
26
1. Remove blower compartment door to gain access to
the thermostat low voltage wires located at the furnace
integrated control module.
2. Remove the thermostat low voltage wires at the furnace
integrated control module terminals.
With Power On (and Door Interlock Switch closed):
L
I
N
E
V
OLTAG
E
NO
W
P
RESE
NT
WARNING
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.
CHECKING AIR CIRCULATOR BLOWER MOTOR
D
IS
CONN
E
CT
ALL
PO
WER
B
E
FO
RE
SERVI
C
I
NG.
WARNING
1. Remove blower compartment door to gain access to the
circulator blower motor and integrated ignition control.
2. Disconnect the motor wire leads from its connection point
at the integrated ignition control module and capacitor if
applicable.
3. Using a ohmmeter, test for continuity between each of the
motor leads.
4. Touch one probe of the ohmmeter to the motor frame
(ground) and the other probe in turn to each lead.
If the windings do not test continuous or a reading is obtained
to ground, replace the motor.
5. After completing check and/or replacement of circulator
blower motor or induced draft blower motor, reinstall
blower compartment door.
6. Turn on electrical power and verify proper unit operation.
D
IS
CONN
E
CT
ALL
PO
WER
B
E
FO
RE
SERVI
C
I
NG.
WARNING
CHECKING DUCT STATIC
The maximum and minimum allowable external static
pressures are found in the specification 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 insufficient
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 filters in the furnace, use a draft gauge (inclined
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.
NOTE:
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.
.
Checking Static Pressure
CHECKING TEMPERATURE RISE
The more air (CFM) being delivered through a given furnace,
the less the rise will be; so the less air (CFM) being delivered,
the greater the rise. The temperature rise should be adjusted
in accordance to a given furnace specifications and its
