036-21083-007-A-0404
6
Unitary Products Group
Sequence of Operation
UNIT OPERATION - 7-1/2, 10 & 12-1/2 TON
When the external control calls for cooling at terminal Y1:
The system controller (SC) is energized. The system control-
ler starts the compressors and enables the condenser fans
by energizing contactor 1M (2M on the 10 and 12-1/2 ton,
208/230 volt models).
The single condenser fan is energized with the compressor
on the 7-1/2 ton models.
Condenser fan motor #1 is energized with the compressors
on the 10 and 12-1/2 ton models while fan #2 is enabled with
compressor operation. Fan motor #2 operation is controlled
through the Ambient Temperature Switch (ATS) which will
de-energize the motor when the ambient temperature falls
below 70
°
F
Safety Lockout: The system controller (SC) has a lockout cir-
cuit to prevent compressor short-cycling on a safety control
with automatic reset. If the high or low refrigerant pressure
switches (HP or LP) open, the SC will enter lockout mode.
SC provides a 90 second bypass of the low pressure switch
LP to prevent nuisance lockouts during unit start-up.
A malfunction light (24V, 2 A max. resistive load) can be
energized through SC, by connecting the light between termi-
nals X and B on TB1.
NOTE: To reset the unit after a lockout:
a.
Turn the system switch on the thermostat to the “OFF”
position and back to the ”COOL” position.
OR
b.
Increase the set point of the room thermostat above the
temperature in the conditioned space and return it to its
original setting. If the unit continues to be shut down by
one of its safety controls, a service man should be called
to determine the cause of the problem. Repeated reset-
ting of the lockout circuit may damage the unit.
