COOLING SYSTEM
The cooling section is a complete factory package utilizing an
air-cooled condenser. The system is factory-charged with
Refrigerant-22.
The compressors are hermetically sealed, internally sprung
and base-mounted with rubber-insulated hold-down bolts.
The compressors also have inherent (internal) protection. If
there is an abnormal temperature rise in a compressor, the
protector opens to shut down the compressor.
PRELIMINARY OPERATION
After installation has been completed, energize the crankcase
heaters for at least four hours before operating unit. After this
initial warm-up, the compressors should be given three false
starts (energized just long enough to make a few revolutions)
with 5-7 minutes delay between each start before being put into
full time service.
NOTE: Prior to each cooling season, the crankcase heaters
must be energized at least 8 hours before system is
put into operation.
COOLING SEQUENCE OF OPERATION
NO OUTDOOR AIR OPTIONS - When the room thermostat
calls for “first-stage” cooling, the low voltage control circuit from
“R” to “G” and “Y1” is completed to energize compressor #1,
outdoor fan motor #1, outdoor fan motor #2 (if the ambient
temperature is above 16°C (60
°
F)), and the supply air blower
motor (if the fan switch on the room thermostat is set in the
“AUTO” position).
When the thermostat calls for “second-stage” cooling, the low
voltage control circuit from “R” to “Y2”is completed to energize
compressor #2.
After the thermostat is satisfied and opens, all components
stop simultaneously. The blower motor continues to operate if
the fan switch on the room thermostat is set in the “ON”
position.
The reversing valve is energized thru the “Y1” circuit when the
subbase is in the cooling mode.
The suction line freezestat cuts the compressors out when the
suction line temperature drops below -3°C (26
°
F). This is an
automatic reset device.
ECONOMIZER WITH SINGLE ENTHALPY SENSOR - When
the room thermostat calls for “first-stage” cooling, the low
voltage control circuit from “R” to “G” and “Y1” is completed.
The “R” to “G” circuit energizes the blower motor (if the fan
switch on the room thermostat is set in the “AUTO” position)
and drives the economizer dampers from fully closed to their
minimum position. If the enthalpy of the outdoor air is below the
setpoint of the enthalpy controller (previously determined),
“Y1” energizes the economizer. The dampers modulate to
maintain a constant supply air temperature as monitored by the
discharge air sensor. If the outdoor air enthalpy is above the
setpoint, “Y1” energizes compressor #1, outdoor fan motor #1,
and outdoor fan motor #2 (if the ambient temperature is above
16°C (60
°
F)).
When the thermostat calls for “second-stage” cooling, the low
voltage control circuit from “R” to “Y2” is completed. If the
enthalpy of the outdoor air is below the setpoint of the enthalpy
controller (i.e., first stage has energized the economizer), “Y2”
energizes compressor #1. If the outdoor air is above the
setpoint, “Y2” energizes compressor #2.
After the thermostat is satisfied and opens, all components
stop simultaneously. The blower motor continues to operate if
the fan switch on the room thermostat is set in the “ON”
position.
ECONOMIZER WITH DUAL ENTHALPY SENSORS - The
operation with the dual enthalpy sensors is identical to the
single sensor except that a second enthalpy sensor is mounted
in the return air. This return air sensor allows the economizer to
choose between outdoor air and return air, whichever has the
lowest enthalpy value, to provide maximum operating
efficiency.
ECONOMIZER (SINGLE OR DUAL) WITH POWER
EXHAUST - This system operates as specified above with one
addition. The power exhaust motor is energized whenever the
economizer is chosen by the enthalpy sensor for first stage
cooling, “Y1”. As always, the “R” to “G” connection provides
minimum position but does not provide power exhaust
operation.
MOTORIZED OUTDOOR AIR DAMPERS - This system
operation is the same as the units with no outdoor air options
with one exception. When the “R” to “G” circuit is complete, the
motorized damper drives open to a position set by the
thumbwheel on the damper motor. When the “R” to “G” circuit is
opened, the damper spring returns fully closed.
HEATING SEQUENCE OF OPERATION
The following sequence of operation is based on using a
standard heat pump two-stage heating/two-stage cooling
thermostat/subbase. Economizer (if supplied) operation is not
allowed in the heating mode; however, the minimum position
does operate.
FIRST STAGE HEAT
When the thermostat calls for “heating”, the low voltage control
circuit from “R” to “G”and “W1” (wiring schematic) is completed
to energize the compressors, outdoor fan motors and blower
motor (if subbase is set on auto) simultaneously. If the subbase
has the indoor fan set on “on” the motor will run all of the time.
SECOND STAGE HEAT
If the compressors alone can not satisfy the heating
requirements, second stage heat energizes all the electric heat
(if supplied) thru the “W2” circuit.
035-18895-000-A-0902
12
Unitary Products Group
OPERATION
