LAARS U.H.E. - Service Manual - Manual (Page 8)

LAARS Heating Systems Page 8
1
Thermostat calls for heat.
2
Blower energizes, pressure switch contacts are normally closed. If the pressure switch contacts are open, blower operates for up to
5 minutes waiting for contacts to close, then blower stops and flashes red PURGE LED indicating lock-out condition.
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6
Steady state operation.
Ignition module monitors:
- Thermostat circuit.
- When thermostat opens, gas valve is shut down and post purge begins.
- Safety circuit.
- If vent temperature switch opens, gas valve is shut down, system will post purge and wait for switch to close
before attempting re-ignition.
- If the blocked vent pressure switch opens, indicating a blocked exhaust vent condition, the gas valve is shut
down, blower shuts down for 30 seconds and is re-energized and system attempts re-ignition if the pressure
switch is closed. Blower operates for 5 minutes to wait for pressure switch to close, then shuts off with purge
light flashing (lock-out). Will restart in 1 hour to attempt to close the switch and restart ignition sequence.
- Flame sensor circuit.
- If flame is lost, gas valve is shut down, system will post purge and system attempts re-ignition.
Prior to energizing blower, ignition module checks to make sure the vent temperature switch is in the normally closed
position. If the vent temperature switch is open, the control waits indefinitely for the temperature switch to close.
Blower pre-purge period (5 seconds) indicated by PURGE LED on the module
4 Igniter warm up (18 seconds), indicated by the IGNITER LED on the module. Note: The blocked vent pressure switch
must be in the normally closed position for the ignition cycle to start.
5
Trial for Ignition (4 seconds, 3 trials).
a) Flame establishing period (2.5 seconds), gas valve and igniter on, indicated by the IGNITER and VALVE LED on the
module.
b) Burner on, flame proving period (1.5 seconds, looking for minimum of 1 micro amps), indicated by the FLAME &
VALVE LED on the module.
7 Thermostat satisfied.
8 Burner off.
9 Blower post purge (15 seconds).
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