13
NORMAL SEQUENCES OF OPERATION
Heating
This unit is equipped with an ignition control that
automatically lights the main burner. DO NOT attempt to
light the main burners by any other method.
1. R and W thermostat contacts close, initiating a call for
heat.
2. Integrated control module performs safety circuit
checks.
3. Inducer draft blower is energized for 30 second pre-
purge period causing pressure sensor contacts to
close.
4. At the end of pre-purge period, integrated control
module transitions the induced draft blower to light-off
setting.
5.
Once the light-off pressure setting is verified by the
integrated control module, the spark igniter and gas
valve are energized for 4 seconds.
NOTE: The igniter produces a very intense
electrical spark that ignites the gas.
6.
Integrated control module monitors flame presence.
Gas valve will remain open only if the flame is
detected.
7. The 5-second HEAT FAN ON delay time begins after
main burner lights.
8. The unit delivers heat to the conditioned space until
the thermostat is satisfied; integrated control module
monitors safety circuits continuously.
9. R and W thermostat contacts open, completing the
call for heat; gas valve de-energizes.
10. Induced draft blower keeps operating for 30-second
post purge.
11. Ignition control begins timing the HEAT FAN OFF
delay. There is an adjustable HEAT FAN OFF delay of
approximately 90/120/150/180 seconds (factory set at
150).
NOTE: This delay allows any additional heat in
the heat exchanger to be transferred to the
conditioned space. After the HEAT FAN OFF delay
time has elapsed, the blower will de-energize.
Cooling
1. Thermostat calls for low or high stage cooling.
2. If the thermostat call is for low stage cooling, the
compressor and outdoor fan are energized at low
stage. If the thermostat call is for high stage cooling,
the compressor and outdoor fan are energized at high
stage.
3. The indoor blower will energize approximately 6
seconds later.
4. The unit delivers cooling to the conditioned space until
the thermostat is satisfied.
5. The compressor and outdoor fan will be de-energized
when the thermostat opens.
6. The indoor blower continues to run at low cool speed
for approximately 60 seconds after the thermostat is
satisfied. This allows additional cooling from the indoor
coil to be transferred to the conditioned space. Then,
the indoor blower is de-energized.
NOTE: A 180-second anti-short cycle is integral
to the control and prevents recycling of the
compressor.
Fan Only
1. Thermostat calls for FAN ONLY by energizing “G”.
2. Indoor blower is energized at fan only speed.
3. The indoor blower is immediately de-energized once
thermostat call for FAN is removed.
STARTUP, ADJUSTMENTS, AND CHECKS
Heating Startup
This unit is equipped with an electronic ignition device to
automatically light the main burners. It also has a power
vent blower to exhaust combustion products.
On new installations, or if a major component has been
replaced, the operation of the unit must be checked.
Check unit operation as outlined in the following
instructions. If any sparking, odors, or unusual sounds are
encountered, shut off electrical power and check for wiring
errors, or obstructions in or near the blower motors. Duct
covers must be removed before operating unit.
Burner Limit Control
The burner temperature switch is mounted on the burner
box assembly to monitor the burner box temperature. It is
normally closed (electrically), auto-reset sensor. An input
to the control is provided by the normally closed blocked
burner switch. An open blocked burner switch interrupts
current to the gas valve which closes the valve. This switch
guards against the burner flames not being properly drawn
into the heat exchanger.
Secondary Limit Control
The secondary limit control is located on the top of the
blower scroll assembly. This control opens when elevated
temperatures are sensed. Elevated temperatures at the
control are normally caused by blower failure. The reason
for the opening should be determined and repaired prior to
resetting.
If the power to the unit is interrupted during the heating
cycle, it may cause the secondary limit to trip. Once the
blower compartment temperature drops below the limit
reset temperature, the limit will automatically reset.
