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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.
Cooling System Performance Values
Model
Superheat +/- 3°
2 Ton
2.5 Ton
3 Ton
3.5 Ton
4 Ton
5 Ton
Based on outdoor ambient temperature of 82°F, and indoor
entering air of 80°F db, 67°F wb.
Ensure unit is installed per manufacturer's instructions and
that line voltage and air flow are correct. Refer to Table 3
for proper performance value. The indoor metering device
varies by model. When checking performance of a unit
using an orifice for metering, refer to the suction superheat
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.
Continuous Fan
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 signals the
ignition control to energize the combustion air blower
at ignition speed.
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. Combustion air
Suction
Liquid
Subcooling +/- 2°
13
16
14
14
16
17
Table 3.
blower ramps from ignition speed to continuous run
speed.
4.
If the flame sensor does not sense that a flame has
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
third trial, flame still has not been established, then the
ignition control will try to light again 1 hour later. The
1-hour retry is indefinite. The ignition control can be
reset by interrupting the unit power or the thermostat
circuit.
6.
Once flame sense has been established, the circulating
air blower is energized after a 30 second blower on
delay.
7.
When the thermostat is satisfied, the combustion air
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.
Blower Delay – Heating
•
The circulating air blower "ON" delay is 30 seconds
after "W" signal is received to allow the furnace to
warm up.
•
The circulating air blower "OFF" delay is 180 seconds
after shutting down the burners. This delay is not
adjustable.
Safety Controls
The control circuit includes the following safety controls:
Limit Control
This control is located behind the heat exchanger access
panel and is designed to open at abnormally high circulating
air temperatures. It resets automatically. The limit control
operates when a high temperature condition, caused by
inadequate airflow, occurs. This closes the main gas valve.
Pressure Switch
If the combustion air blower should fail, the pressure
switch prevents the spark electrode and gas valve from
being energized.
Flame Sensor
If the ignition control does not receive a signal from the
flame sensor indicating that the burners have established
flame, the gas valve closes after the 10-second trial for
ignition period.
Burner Temperature Switch
The burner temperature switch is located on the combustion
air intake elbow adjacent to the gas manifold. In the event
of excessive burner heat, the switch shuts off the ignition
control and closes the main gas valve. The switch resets
automatically.
Page 15
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