Honeywell ST9120B Mode D'emploi page 13

CHECKOUT
Operate the system through at least one complete
heating cycle and cooling cycle to make sure the system
operates properly. Troubleshoot by checking for
Action
Thermostat begins call for heat.
(Terminal W is energized.)
Thermostat ends call for heat.
(Terminal W is de-energized.)
Thermostat begins call for cool.
(Terminal Y is energized.)
Thermostat ends call for cool.
(Terminal Y is de-energized.)
Thermostat begins call for fan.
(Terminal G is energized.)
Thermostat ends call for fan.
(Terminal G is de-energized.)
Limit switch string opens.
Limit switch string remakes.
Continuous circulating fan is
connected.
(Optional connection to circulating
fan low speed tap)
Electronic air cleaner is connected.
(Optional connection to line voltage
powered electronic air cleaner)
Humidity control is connected.
(Optional connection to line voltage
powered humidifier)
Action
Thermostat begins call for heat.
(Terminal W is energized.)
Thermostat ends call for heat.
(Terminal W is de-energized.)
Thermostat begins call for cool.
(Terminal Y is energized.)
Thermostat ends call for cool.
(Terminal Y is de-energized.)\
Table 7. ST9120 Operation Mode.
1. Inducer is energized.
2. Pressure switch makes (air flow is established).
3. Ignition system is energized.
4. Gas valve opens and main burner lights.
5. Heat fan-on delay timing begins. When timing is complete, circulating fan is
energized at heat speed.
1. Ignition system is de-energized and gas valve closes.
2. Inducer is de-energized after postpurge timing.
3. Heat fan-off delay timing begins. When timing is complete, the circulating
fan is de-energized.
1. Cooling contactor is energized.
2. Circulating fan is energized at cool speed after cool fan-on delay timing.
1. Cooling contactor is de-energized.
2. Circulating fan is de-energized after cool fan-off delay timing.
1. Circulating fan is energized at heat speed.
2. If call for heat occurs, circulating fan continues to run at heat speed.
3. If call for cool occurs, circulating fan switches to cool speed.
NOTE: Circulating fan can be switched off for one second during the transition
between the fan speeds.
1. Circulating fan is de-energized.
1. Thermostat and ignition system are de-energized and gas valve closes.
2. Inducer and circulating fan heat speed are energized.
3. LED flashes once.
1. Inducer remains energized for postpurge timing.
2. The circulating fan remains energized for the selected delay-off timing.
3. Normal operation resumes.
1. Circulating fan low speed is energized when there is no call for heat, cool,
or fan.
2. If fan operation is required by a call for heat, cool, or fan, ST9120B,U
switches circulating fan to appropriate speed.
1. In two-speed systems, the electronic air cleaner is energized when the
heat or cool speed of the circulating fan is energized.
2. If continuous fan option is used, connect EAC to line voltage input L1.
1. Humidifier is energized when Inducer is energized.
Table 8. ST9141 Operation Mode.
1. Pressure switch to be confirmed in no airflow position. (if pressure switch
shows airflow, LED flashes three times).
2. Inducer is energized.
3. Pressure switch makes (if pressure switch shows no airflow for 30 s, LED
starts flashing three times).
4. Ignition system is energized.
5. Gas valve opens and main burner lights.
1. Ignition system is de-energized and gas valve closes.
2. Inducer is de-energized after postpurge timing.
3. Heat fan-off delay timing begins. When timing is complete, the circulating
fan is de-energized.
1. Cooling contactor is energized.
2. Circulating fan is energized at cool speed after cool fan-on delay timing.
1. Cooling contactor is de-energized.
2. Circulating fan is de-energized after cool fan-off delay timing.
ST9120B,U UNIVERSAL ELECTRONIC FAN TIMERS
appropriate voltages at the ST9120B,U terminals
controlling the combustion blower and heat and cool
speed circulating fan. The ST9120B,U schematics show
internal switching to clarify operation and assist in
troubleshooting. See Figs. 5 and 6.
System Response
System response
13 69-2252EF—07