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Page 10 of 13 507295-02Cmrcool.com
Operation
Cooling System
The cooling system is factory-charged with HFC-R-410A.
The compressor is hermetically sealed and base-mounted
with rubber-insulated bolts.
Cooling Sequence of Operation
When the thermostat calls for cooling, R is closed to Y (see
the wiring diagrams). This action completes the low voltage
control circuit, energizing the compressor, condenser fan
motor, and blower motor.
Unit compressors have internal protection. In the event there
is an abnormal rise in the temperature of the compressor,
the protector will open and cause the compressor to stop.
Blower Delay – Cooling
The circulating air blower is controlled by a timing circuit
in the integrated blower/ignition control. Timings are not
adjustable. Blower “ON” delay is 5 seconds after the
compressor starts and blower “OFF” timing is 60 seconds
after the compressor shuts down.
NOTE: There is no blower OFF delay when there is a call
for G (fan only).
Cooling System Performance
This equipment is a self-contained, factory-optimized
refrigerant system. The unit should not require adjustments
to system charge when properly installed. If unit
performance is questioned, perform the following checks.
Ensure unit is installed per manufacturer’s instructions and
for proper performance value. The indoor metering device
varies by model. When checking performance of a unit
value to judge performance. When checking performance
of a unit that uses an expansion valve for metering, refer
to the subcooling value to judge system performance. If
the measured performance value varies from table value
allowance, check internal seals, service panels and duct
work for air leaks, as well as restrictions and blower
speed settings. If unit performance remains questionable,
remove system charge, evacuate to 500 microns, and
weigh in refrigerant to nameplate charge. It is critical that
the exact charge is re-installed. Failure to comply will
compromise system performance. If unit performance is
still questionable, check for refrigerant-related problems,
such as blocked coil or circuits, malfunctioning metering
device or other system components.
Cooling System Performance Values
Model
Suction
Superheat +/- 3°
Liquid
Subcooling +/- 2°
2 Ton 13
2.5 Ton 16
3 Ton 14
3.5 Ton 14
4 Ton 16
5 Ton 17
Based on outdoor ambient temperature of 82°F, and indoor
entering air of 80°F db, 67°F wb.
Table 3.
Heating System
With the proper thermostat and sub-base, continuous
blower operation is possible by closing the R to G circuit.
Cooling blower delay is also functional in this mode.
Heating Sequence of Operation
When the thermostat calls for heating, R is closed to W. The
following describes the gas heating sequence of operation.
1. A call for heat from the room thermostat starts the
combustion air blower and the circulating air blower.
2. When the speed of the combustion air blower reaches
proper RPM, the pressure switch closes, initiating a
pre-purge period (30 seconds nominal).
3. When the pre-purge period has expired, the ignition
control energizes the main gas valve and spark
electrode for a period of 10 seconds.
4.
been established in the 10-second interval, then the
ignition control will de-energize the gas valve, and
begins a 30 second inter-purge period, then initiates
another trial for ignition.
5. The ignition control is designed to repeat this “trial
for ignition” a total of three times. If, at the end of the
ignition control will try to light again 1 hour later. The
reset by interrupting the unit power or the thermostat
circuit.
6.
air blower is energized after a 30 second blower on
delay.
7.
blower and gas valve are de-energized. The circulation
air blower will continue to run for a short period after
the furnace is shut down.
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