COOLING SYSTEM
The cooling section is a complete factory package utilizing an
air-cooled condenser. The system is factory-charged with
Refrigerant-22. The scroll compressor is hermetically sealed
and internally sprung.
The scroll compressors have inherent (internal) protection. If
there is an abnormal temperature rise in the scroll compressor,
the protector will open to shut down the scroll compressor.
COOLING SEQUENCE OF OPERATION
Single-Stage Cooling:
When the thermostat calls for “cooling”, “R” is closed to “G” and
“Y1" (wiring schematic) which completes the low voltage
control circuit, immediately energizing the scroll 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 provided by the economizer
if the outdoor air enthalpy is acceptable, and second-stage
cooling is provided by the scroll 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 evaporator
temperatures due to a low air flow or a low return air
temperature.
2. A High Pressure Cutout Switch to protect against excessive
discharge pressures due to a blocked condenser coil or a
condenser motor failure.
3. A Low Pressure 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
HEATING MODE
Single-Stage Heating:
a. If the fan switch is in the “ON” position, the evaporator
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 always
the first and last to complete its timing cycle and controls
power to the evaporator blower motor.
c. The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
Two-Stage Heating:
a. If the fan switch is in the “ON” position, the evaporator
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 first-stage heat by the thermostat, the first
stage of heat will be energized.
If the thermostat calls for the second stage of heat, the
second stage of heat will be energized.
As before, sequencer 1S (or contactor 2M) maintains
control of the evaporator blower.
c. The thermostat will cycle the electric heat to satisfy the
heating requirements of the conditioned space.
CONTINUOUS BLOWER - Continuous blower operation is
possible by closing the R to G circuit on the thermostat.
HEAT ANTICIPATOR SETPOINTS
It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON” cycles
and may result in the lowering of the temperature within the
conditioned space. Refer to Table 10 for the required heat
anticipator setting.
CHECKING SUPPLY AIR CFM
The speed of the supply air blower will depend on the required
CFM, the unit accessories and the static resistances of both
the supply and the return air duct systems. With this
information, the speed for the supply air blower can be
determined from the static resistance and blower performance
data on Tables 3 thru 6.
Knowing the required blower RPM and the blower motor HP,
the speed setting for the direct-drive supply air motor can be
determined.
OPERATION
NOMINAL
HEATER
SIZE
KW
VOLTAGE
SETTING, AMPS
TH1
TH2
5
7
10
15
20
30
240-1-60
0.16
0.35
0.35
0.35
0.35
0.35
-
-
-
0.19
0.38
0.38
5
7
10
15
20
30
240-3-60
0.35
0.35
0.35
0.35
0.35
0.35
-
-
-
0.19
0.38
0.38
7
10
15
20
30
480-3-60
0.35
0.35
0.35
0.37
0.37
-
-
-
0.29
0.29
10
15
20
30
600-3-60
0.35
0.35
0.37
0.37
-
-
0.29
0.29
TABLE 14 - HEAT ANTICIPATOR SETTING
530.18-N7Y
14
Unitary Products Group
