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. Check for loose wiring between the contactor and the sup- ply 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.
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 compres- sor #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 com- pressor.
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
46 | Johnson Controls Unitary Products |
