284806-YIM-A-0107
Unitary Products Group
51
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
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.
7.
If 24 volts is not present at M3, check that 24 volts
is present at the UCB supply air blower motor ter-
minal, “FAN”. If 24 volts is present at the FAN,
check for loose wiring between the UCB and M3.
8.
If 24 volts is not present at the “FAN” terminal,
check for 24 volts from the room thermostat. If 24
volts are not present from the room thermostat,
check for the following:
a.
proper operation of the room thermostat (contact
between R and G with the fan switch in the ON posi-
tion and in the AUTO position during operation
calls), b. proper wiring between the room thermostat
and the UCB, and c. loose wiring from the room
thermostat to the UCB.
9.
If 24 volts is present at the room thermostat but not
at the UCB, check for proper wiring between the
thermostat and the UCB, i.e. that the thermostat G
terminal is connected to the G terminal of the UCB,
and for loose wiring.
10. If the thermostat and UCB are properly wired,
replace the UCB.
On calls for cooling, the supply air blower motor is
operating but compressor #1 is not (the room thermo-
stat fan switch is in the “AUTO” position).
1.
If installed, check the position of the economizer
blades. If the blades are open, the economizer is
providing free cooling and the compressors will not
immediately operate. If both stages of cooling are
requested simultaneously and the economizer pro-
vides free cooling, following a short delay compres-
sor #1 will be energized unless it is locked out. If
compressor #1 is locked out, compressor #2 is
energized. Compressor #2 is always energized in
place of compressor #1 when compressor #1 is
requested but locked out.
2.
If no economizer is installed or the economizer is not
opening to provide free cooling and compressor #1
does not energize on a call for cooling, check for line
voltage at the compressor contactor, M1, and that
the contactor is pulled in. Check for loose wiring
between the contactor and the compressor.
3.
If M1 is pulled in and voltage is supplied at M1,
lightly touch the compressor housing. If it is hot, the
compressor may be off on inherent protection.
Cancel any calls for cooling and wait for the inter-
nal overload to reset. Test again when cool.
4.
If M1 is not pulled in, check for 24 volts at the M1
coil. If 24 volts are present and M1 is not pulled in,
replace the contactor.
5.
Failing the above, if voltage is supplied at M1, M1
is pulled in, and the compressor still does not oper-
ate, replace the compressor.
6.
If 24 volts is not present at M1, check for 24 volts at
the UCB terminal, C1. If 24 volts is present, check
for loose wiring between C1 and the compressor
contactor.
