284806-YIM-A-0107
Unitary Products Group
55
14. If none of the above corrected the error, test the
integrity of the UCB. Disconnect the C1 terminal
wire and jumper it to the Y1 terminal. DO NOT
jump the Y1 to C1 terminals. If the compressor
engages, the UCB has faulted.
15. If none of the above correct the error, replace the
UCB.
GAS HEAT TROUBLESHOOTING GUIDE
NOTE:
To find the Btu input, multiply the number of
cubic feet of gas consumed per hour by the
Btu content of the gas in your particular locality
(contact your gas company for this information
- it varies widely from city to city.).
On calls for heating, the draft motor operates and the
furnace lights but the supply air blower motor does not
energize after a short delay (the room thermostat fan
switch is in “AUTO” position).
1.
Place the thermostat fan switch in the “ON” posi-
tion. If the supply air blower motor energizes, go to
Step 10.
2.
If the supply air blower motor does not energize
when the fan switch is set to “ON,” check that line
voltage is being supplied to the contacts of the M3
contactor, and that the contactor is pulled in. For
units with VFD, check that line voltage is being
supplied to the M3-Auxiliary contacts. Check for
loose wiring between the contactor and the supply
air blower motor.
3.
If M3 is pulled in and voltage is supplied at M3,
lightly touch the supply air blower motor housing. If
it is hot, the motor may be off on inherent protec-
tion. Cancel any thermostat calls and set the fan
switch to “AUTO”, wait for the internal overload to
reset. Test again when cool.
4.
If M3 is not pulled in, check for 24 volts at the M3
coil. If 24 volts is present at M3 but M3 is not pulled
in, replace the contactor.
5.
Failing the above, if there is line voltage supplied at
M3, M3 is pulled in, and the supply air blower
motor still does not operate, replace the motor.
For units with VFD, if there is line voltage supplied
at M3, M3 is pulled in, and the blower motor does
not operate, check all power & control wiring con-
nections to and from the drive and for any fault/
warning messages displayed on the drive's digital
display (refer to the drive user manual for full
descriptions, if necessary). Clear any fault by
pressing 'RESET' on the drive's keypad and take
any corrective action as needed. If the motor still
does not operate, replace the motor.
Troubleshooting of components may require
opening the electrical control box with the
power connected to the unit.
Use extreme care
when working with live circuits!
Check the
unit nameplate for the correct line voltage and
set the voltmeter to the correct range before
making any connections with line terminals.
For troubleshooting of optional VFD, discon-
nect all power to the drive. Be aware that high
voltages are present in the drive even after
power has been disconnected. Capacitors
within the drive must be allowed to discharge
before beginning service.
When not necessary, shut off all electric power to
the unit prior to any of the following maintenance
procedures so as to prevent personal injury.
Label all wires prior to disconnection when ser-
vicing controls. Wiring errors can cause
improper and dangerous operation, which could
cause injury to person and/or damage unit com-
ponents. Verify proper operation after servicing.
The furnace may shut down on a high temper-
ature condition during the procedure. If this
occurs, the UCB energize the supply air blower
motor until the high temperature limit has reset.
Caution should be used at all times as the sup-
ply air blower may energize regardless of the
room thermostat fan switch position.
