Installation, Operation and Maintenance Manual : 036-1011(0806)
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TROUBLE SHOOTING
COOLING TROUBLE SHOOTING GUIDE
WARNING
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.
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.
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
SERVICING 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.
CAUTION
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 compressor has
energized when the fan switch is in the AUTO position,
check the room thermostat for contact 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 blower contactor, and that the
contactor is pulled in. Check for loose wiring between the
contactor and the supply air blower motor.
4. If blower contactor is pulled in and voltage is supplied to
contactor, lightly touch the supply air blower motor
housing. If it is hot, the motor may be off on internal
protection. Cancel any thermostat calls and set the fan
switch to AUTO. Wait for the internal overload to reset.
Test again when cool.
5. If blower contactor is not pulled in, check for 24 volts at
the contactor coil. If 24 volts are present but it is not
pulled in, replace the contactor.
6. Failing the above, if there is line voltage supplied at
contactor and it is pulled in, and the supply air blower
motor still does not operate, replace the motor.
7. If 24 volts is not present at blower contactor, check that
24 volts is present at the UCB supply air blower motor
terminal, “FAN”. If 24 volts is present at the FAN, check
for loose wiring between the UCB and blower contactor.
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
position 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 thermostat fan switch is
in the “AUTO” position).
1. If compressor # 1 does not energize on a call for cooling,
check for line voltage at the compressor contactor 1, and
that the contactor is pulled in. Check for loose wiring
between the contactor and the compressor.
2. If compressor contactor 1 is pulled in and voltage is
supplied, 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 internal
overload to reset. Test again when cool.
SHUT DOWN
1. Set the thermostat to highest temperature setting.
2. Turn off the electrical power to the unit.
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. For high static
requirement (DMS 480 & 600), fixed pitch pulleys will be
provided.
