035-13329-001-B-0504
Unitary Products Group
15
OPERATION
COOLING SYSTEM
The cooling section is a complete factory package utilizing an
air-cooled condenser. The system is factory-charged with
Refrigerant-22. The compressor is hermetically sealed and
internally sprung.
The compressors have inherent (internal) protection. If there
is an abnormal temperature rise in the compressor, the pro-
tector will open to shut down the compressor.
PRELIMINARY OPERATION COOLING
After the installation has been completed, the crankcase
heater of the compressor must be energized for at least 4
hours before starting the unit. After this initial warm-up, the
compressor should be given three false starts (energized just
long enough to make a few revolutions) with a 5 minute delay
between each start before being put into full time service.
NOTE: Prior to each cooling season, the crankcase heater
must be energized at least 10 hours before the sys-
tem is put into operation.
COOLING SEQUENCE OF OPERATION
Single-Stage Cooling: When the thermostat calls for “cool-
ing”, “R” is closed to “G” and “Y1" (wiring schematic) which
completes the low voltage control circuit, immediately ener-
gizing the compressors, condenser fan motor and blower
motor simultaneously.
Two-Stage Cooling: A two-stage cooling thermostat may be
used if the unit has an economizer. First-stage cooling is pro-
vided by the economizer if the outdoor air enthalpy is accept-
able, and second-stage cooling is provided by the
compressor. Jumper wire J1 must be removed. Refer to unit
wiring diagram.
After the thermostat is satisfied and opens, the blower will
continue to run for a short time. All other components will
stop.
SAFETY CONTROLS
The refrigerant system is equipped with the following safety
controls:
1.
A Suction Line Freezestat to protect against low evapo-
rator temperatures due to a low air flow or a low return
air temperature.
2.
A High Pressure Cutout Switch to protect against exces-
sive discharge pressures due to a blocked condenser
coil or a condenser motor failure.
3.
A Low Pressure/Loss of Charge Switch to protect
against loss of refrigerant charge.
If either of the above safety controls opens, the refrigerant
system will be locked out. The lock out of the system can be
reset by opening the 24V circuit either at the room thermostat
or at the unit disconnect.
HEATING SEQUENCE OF OPERATION
The following sequence of operation is based on using a
standard single-stage or two-stage heating thermostat.
WITH POWER TO UNIT AND THERMOSTAT IN THE HEAT-
ING MODE
Single-Stage Heating:
a.
If the fan switch is in the “ON” position, the evapora-
tor blower motor relay (BR) will be energized
through terminal G to provide continuous blower
operation. If the fan switch is in the “AUTO” position,
the blower will operate only when there is a call for
heating by the thermostat.
b.
Upon a call for heat by the thermostat, the first stage
of heat will be energized. Sequencer 1S (or
contactor 2M) is al-ways the first and last to com-
plete its timing cycle and controls power to the evap-
orator blower motor.
c.
The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
