035-17438-001 Rev. A (901)
Unitary Products Group
23
MOTOR OPERATION IS INTERMITTENT
•
Verify that all connectors are firmly seated. Gently pull
the motor connector wires at both ends of the cables
individually to be sure they are properly crimped into the
housings.
MOTOR RUNS WHEN IT IS SUPPOSED TO BE OFF
•
Allow a few minutes for the motor to shut off. Motor-off
delays are controlled by the ignition control.
MOTOR STARTS BUT: RUNS ERRATICALLY
•
Check the line voltage for variation.
•
Check low voltage connections at motor, unseated pins
in motor harness connectors.
•
Check “Bk” for erratic CFM command.
MOTOR HUNTS OR “PUFFS”
•
Excessive restriction in duct system or filter. Reduce
maximum air flow.
STAYS AT LOW CFM DESPITE SYSTEM CALL FOR
COOL OR HEAT CFM
•
Check low voltage wires and connections.
•
Verify fan is not in delay mode - wait until delay is com-
plete.
•
“R” missing /not connected at motor or terminal strip.
•
Perform motor/control replacement check.
STAYS AT HIGH CFM
•
“R” missing/not connected at motor or terminal strip.
•
Is fan in delay mode? Wait until delay is complete.
•
Perform motor/control replacement check.
BLOWER WON’T SHUT OFF
•
Current leakage from controls into G, Y, or W? Check for
Triac switched thermostat or solid state relay.
EXCESSIVE NOISE
•
Determine if it’s air noise, cabinet, duct, or motor noise.
AIR NOISE
•
Check for loose blower housing, panels, etc.
•
High static creating high blower speed?
REPLACEMENT OF FAILED MOTOR CONTROL
MODULE
NOTE:
The motor control module may be removed and
BLOWER REMOVAL FOR CONTROLLER
REPLACEMENT
•
Refer to “BLOWER CARE” on page 21 of this manual for
blower removal instructions.
•
Rest the blower on its side so the end of the motor is
accessible and facing up.
•
Wait at least 5 minutes after disconnecting AC power
from the furnace before opening the motor.
•
Remove the 2-1/4” Hex head bolts from the motor while
holding the control module.
•
Verify with an ohmmeter that the resistance of each
motor lead is greater than 100K ohms by connecting one
meter lead to the motor lead and the other to an
unpainted portion of the motor housing. If any one of the
leads fails this test THE MOTOR IS DEFECTIVE AND
MUST BE REPLACED.
•
Verify that the replacement control module is the correct
one and carefully orient the control module close to the
motor so the cable can be plugged into the module. BE
SURE THE PLUG LATCHES WITH A CLICK.
•
Carefully align the locating pin of the control module with
the matching motor hole. Replace the 2-1/4” hex head
bolts and tighten snugly. DO NOT OVERTIGHTEN.
You must have the correct replacement control
module for the furnace being serviced. The con-
trols are factory programmed for specific operating
modes. Consult the parts list supplied with this fur-
nace to obtain the correct part number before
ordering the part.
Using the wrong control module voids all product
warranties and may produce unexpected results.
When the hex bolts are removed from the control
module, the module is free from the motor but still
connected by a plug and cable. Carefully rotate
the control so as to gain access the plug on the
end of cable. Squeeze the release latch and gently
pull the plug out of the control module. Do not pull
on the wires.
