Sequence Of Operation - Heating; Sequence Of Operation - Cooling - Bard WG Series Installation Instructions Manual

31. 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
ignitor 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.
Once the problem has been resolved, reset the
switch by pressing down on the reset button on
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 2100-587J
Page 38 of 59
FIGURE 17
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.
top of the switch. See Figure 17 for additional
information.
32. SEQUENCE OF OPERATION –
COOLING
Non-Economizer
Stage 1 (Y1) cooling call activates Step 1 (partial
capacity, 66%) of compressor capacity.
Stage 2 (Y2) cooling call activates Step 2 (full
capacity, 100%) of compressor capacity.
With Economizer
Stage 1 (Y1) cooling call goes to economizer controls
for decision:
• If enthalpy control decides outdoor conditions
are suitable for free cooling, the economizer will
operate.
- If Stage 2 cooling call is issued during
economizer operation, the economizer will
close and the compressor will go straight to
Step 2 full capacity operation.
• If enthalpy control decides outdoor conditions
are not suitable for free cooling, the economizer
will not operate (or close) and Step 1 of the
compressor will operate.
- If Stage 2 cooling call is issued, the
compressor will shift to Step 2 full cooling
capacity operation.