284816-BIM-B-0707
56
Unitary Products Group
ADJUSTMENT OF TEMPERATURE RISE
The temperature rise (or temperature difference
between the return air and the heated air from the fur-
nace) must lie within the range shown on the rating
plate and the data in the Gas Heat Application Table 4.
After the temperature rise has been determined, the
cfm can be calculated as follows:
After about 20 minutes of operation, determine the fur-
nace temperature rise. Take readings of both the return
air and the heated air in the ducts (about six feet from
the furnace) where they will not be affected by radiant
heat. Increase the blower cfm to decrease the temper-
ature rise; decrease the blower cfm to increase the
rise. Refer to the Blower Motor and Drive Data
Table 21.
BELT DRIVE BLOWER
All units have belt drive single-speed blower motors.
The variable pitch pulley on the blower motor can be
adjusted to obtain the desired supply air CFM.
TROUBLESHOOTING
COOLING TROUBLESHOOTING GUIDE
On calls for cooling, if the compressors are operating
but the supply air blower motor does not energize after
a short delay (the room thermostat fan switch is in the
“AUTO” position).
1.
Turn the thermostat fan switch to the ON position.
If the supply air blower motor does not energize, go
to Step 3.
2.
If the blower motor runs with the fan switch in the
ON position but will not run after the first compres-
sor has energized when the fan switch is in the
AUTO position, check the room thermostat for con-
tact between R and G in the AUTO position during
calls for cooling.
3.
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.
4.
If M3 is pulled in and voltage is supplied to M3,
lightly touch the supply air blower motor housing. If
it is hot, the motor may be off on internal protec-
tion. Cancel any thermostat calls and set the fan
switch to AUTO. Wait for the internal overload to
reset. Test again when cool.
5.
If M3 is not pulled in, check for 24 volts at the M3
coil. If 24 volts are present at M3 but M3 is not
pulled in, replace the contactor.
6.
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
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 termi-
nals.
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 mainte-
nance procedures so as to prevent personal
injury.
CFM
Btuh Input x 0.8
=
108
.
.
x F Temp Rise
o
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 components. Verify proper operation after
servicing.