Sequence Of Operation - Heating; Sequence Of Operation - Cooling; Figure 22 Sequence Of Operation - Electronic Blower Control - Bard W24G4 Installation Instructions Manual

32. SEQUENCE OF OPERATION –
HEATING
On a call for heat from the thermostat, the induced
draft blower is energized. Once sufficient draft is
established, the pressure switch contacts close and
the ignition system is energized. The direct spark
igniter will be energized allowing gas to flow. At the
same time the main valve is energized, a 30-second
blower delay timer is activated.
After this delay, the heating speed blower relay
energizes. The blower will begin operating and remain
in operation until the set delay time after the call
for heat has been satisfied. This timing sequence
guarantees blower on, blower off operation.
This unit is equipped with a flame roll-out switch,
which is wired in series with the control circuit. This
is a manual reset switch and is used for the purpose
of preventing possible fire hazard in the event of a
system malfunction. If this switch has opened the
control circuit, there could be a possible system
malfunction. Some of the conditions that might cause
a roll-out to occur are blockage or sooting of primary
heat exchanger, overfiring of furnace due to improper
main burner orifices or incorrect manifold pressure,
insufficient combustion air or installation deficiencies
with respect to return air duct design or sizing.
Action
Thermostat calls for heat
(W terminal is energized).
Thermostat ends call for heat.
Thermostat begins call for cool
(G and Y terminals re-energized).
Thermostat begins call for fan
(G terminal is de-energized).
Limit (flame rollout) opens.
Limit (auto reset) or flame rollout
(manual reset) circuit closed.
Manual 2100-721B
Page 42 of 54
Once the problem has been resolved, reset the switch
by pressing down on the reset button on top of the
switch. See Figure 22 for additional information.
33. SEQUENCE OF OPERATION –
On a call for cooling from the room thermostat, the
blower relay will be energized as well as the compressor
contactor. Following termination of the cooling cycle,
the blower motor will continue to run for one minute.
See Figure 22 for additional information.
The unit may be equipped with a low ambient control
for lower outdoor temperature operation in the cooling
mode. If equipped with this optional control, the
condenser fan will not operate immediately upon
compressor start-up, and will cycle on and off until the
condensing pressure remains above 180 PSIG. Low
ambient control energizes the fan motor at 280 PSIG,
de-energizes at 180 PSIG.
FIGURE 22
Sequence of Operation
Electronic Blower Control
System Response
• Combustion air blower is energized.
• Air proving switch makes. Airflow is established.
• Ignition system is energized.
• Gas valve opens and main burner lights.
• Heat fan on delay timing begins. When timing is complete, the circulating fan is
energized at heat speed.
• Ignition system is de-energized and gas valve closes.
• Combustion air blower is de-energized after postpurge timing.
• Heat fan off delay timing begins. When timing is complete, the circulating fan is
de-energized.
• Cooling contactor is energized.
• Circulating fan is energized on cool speed after cool fan on delay timing.
• Circulating fan is de-energized
• Thermostat and ignition system are de-energized and gas valve closes.
• Combustion air blower and circulating fan heat speed are energized.
• Combustion air blower remains energized for postpurge timing.
• The circulation fan remains energized for the selected delay off timing.
• Normal operation resumes.
COOLING