290699-YIM-B-0607
Unitary Products Group
49
tion, 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.
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.
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 a call for cooling, the supply air blower motor is
operating but the compressor 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 the com-
pressor will be energized unless it is locked out,
unless this option has been disabled through com-
puter communications.
2.
If no economizer is installed or the economizer is not
opening to provide free cooling and the compressor
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.
7.
If 24 volts is not present at the C1 terminal, check
for 24 volts from the room thermostat at the UCB
Y1 terminal. If 24 volts is not present from the room
thermostat, check for the following:
a.
24 volts at the thermostat Y1 terminal
b.
Proper wiring between the room thermostat and the
UCB, i.e. Y1 to Y1, Y2 to Y2
c.
Loose wiring from the room thermostat to the UCB.
8.
If 24 volts is present at the UCB Y1 terminal, the
compressor may be out due to an open high-pres-
sure switch, low-pressure switch, or freezestat.
Check for 24 volts at the HPS1, LPS1, and FS1
terminals of the UCB. If a switch has opened, there
should be a voltage potential between the UCB ter-
minals, e.g. if LPS1 has opened, there will be a 24-
volt potential between the LPS1 terminals.
9.
If 24 volts is present at the UCB Y1 terminal and
none of the protection switches have opened, the
UCB may have locked out the compressor for repeat
trips. The UCB should be flashing an alarm code. If
not, press and release the ALARMS button on the
UCB. The UCB will flash the last five alarms on the
LED. If the compressor is locked out, cancel any call
for cooling. This will reset any compressor lock outs.
