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177820-YIM-A-0506
32 Unitary Products Group
7. Measure evaporator fan motor's amp draw.
8. Set the room thermostat fan switch to off.
9. Turn unit electrical power off.
OPERATING INSTRUCTIONS
1. Turn unit electrical power on.
2. Set the room thermostat setting to lower than the
room temperature.
3. First stage compressors will energize after the
built-in time delay (five minutes).
4. The second stage of the thermostat will energize
second stage compressor if needed.
POST START CHECK LIST
1. Verify proper system pressures for both circuits.
2. Measure the temperature drop across the evapora-
tor coil.
3. Measure the system Amperage draw across all
legs of 3 phase power wires.
4. Measure the condenser fan amp draw.
SHUT DOWN
1. Set the thermostat to highest temperature setting.
2. Turn off the electrical power to the unit.
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 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 contacts of the M2,
contactor, and that the contactor is pulled in. Check
for loose wiring between the contactor and the sup-
ply air blower motor.
4. If M2 is pulled in and voltage is supplied to M2,
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 M2 is not pulled in, check for 24 volts at the M2
coil. If 24 volts are present at M2 but M2 is not
pulled in, replace the contactor.
6. Failing the above, if there is line voltage supplied at
M2, M2 is pulled in, and the supply air blower
motor still does not operate, replace the motor.
7. If 24 volts is not present at M2, 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 M2.
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.
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.
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.