SEQUENCE OF OPERATION
1.When the thermostat calls for heat, relay coil (1M) is energized closing two sets of NO contacts. One set (1M2) energizes the 24 volt limit circuit and the other set (1M1) completes the 120 volt circulator circuit.
2.With the thermal cutout switch (on the burner access panel), the high limit switch, and the suction pressure switch in their normally closed positions, the fan relay coil (2M) is energized closing two sets of NO contacts. One set (2M1) completes the 120 volt fan circuit and the other set (2M2) energizes the 24V suction pressure “check” circuit.
3.With the fan operating, the suction pressure switch closes its NO contacts. The “check” circuit contacts (2M2) keep power on the fan relay (2M) during the heating cycle.
4.When the suction pressure switch proves fan operation the ignition module is energized, beginning a
5.After prepurge, the module energizes the pilot gas valve operator. The pilot gas valve opens, allowing gas to flow to the pilot burner. At the same time, the electronic spark generator in the module generates a spark at the
6.If the pilot does not light within 90 seconds, or the pilot flame current is not at least 1.0 milliamps and steady, the module will not energize the main gas valve and the main burner will not light. Then the module goes into safety lockout,
7.When the sensor senses pilot flame during the 90 second trial for ignition the module will shut off the spark generator, reset the safety lockout timer, and energize the main gas valve operator. The main gas valve opens allowing gas to flow to the main burners where it is ignited by the pilot burner. Since the main gas valve is a
for ignition (low fire). After a short time interval, the regulator on the gas valve will permit full flow through the main gas valve (high fire).
Should a loss of flame occur, the main valve closes and the spark reoccurs within 0.8 second. The ignition module has an internal 100% lockout function to completely shutdown the system should the pilot gas fail to ignite with approx. 90 seconds. Five to six minutes after shutdown, the Ignition Module restarts the ignition sequence. The ignition trial, shutdown, and wait sequence continues until either the pilot lights or the Thermostat is set below room temperature (to end the call for heat). The ignition sequence can be reset by setting down the Thermostat for one minute.
8.Burners, circulator and fan will continue to operate until the thermostat is satisfied.
9.If the high limit setting is reached before the thermostat is satisfied, the switch in the high limit will open to
10.If for any reason (such as flame roll out into the vestibule) the thermal cutoff switch located on the burner access panel is subjected to temperatures above its setting the TCO switch will open to
11.In the event the fan is inoperative or fails to provide sufficient air flow, the suction pressure switch connected at the inlet of the fan will not activate, the NO contacts will not close, the ignition module will not be energized, and hence the gas valves cannot be opened.
12.If the contacts in the suction pressure switch were to weld together during the heating cycle (COM to NO), the ignition module could not be energized on the next call for heat due to the fact the fan relay coil (2M) could not be energized through either the suction pressure switch or the now open “check circuit” contacts.
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