Service Manual

Sequence of Operation
Thermostat Calls for Heat.
Prior to energizing blower,gas control checks safetycircuittoinsure the circuit isopen. Normal switch positions
in the safetycircuit are as follows:
a) Pressure switch normally open.
b) Blower temperature switch normallyclosed.
If the safetycircuit is
closed, the control waits 4 seconds,gas control LED flashes 2 times with 3 second pause.
Gas control waits 2 minutes then, blower runs for 30 seconds. This cycle repeats until safetycircuitopens.
Power up Sequence
1
Start Up.
Uponpower up, the control runs a safe-start check withatypical start-up delay of 1-5 seconds.
2
SimulatedResistive Load Device Check.
To assure no outputs are energized if the “Simulated Resistive device” is out of range, the control will test the
the device for proper operating range. If the device is within range the control resumes normal operationwith no
perceivable delay. If the device isoutofrange, the control LED immediately flashes 7 times with 3 second pause.
Normal Heating Sequence
1
2
Blower Energizes.
3
Pressure Switch Proves Blower/Vent System Operation.
If the pressure switch does not close within 30 seconds, the control LED Flashes 3 times with 3 second pause.
The blower runs for 30 seconds every2minutes trying to get the pressure switchorblower temperature switchto
close. This cycle repeats as long as there isacall for heat.
4
Blower Pre-purge Period(2seconds)
5
Trial for Pilot Ignition(90 seconds).
a) The gas control lights the pilot by activating spark igniter and gas flow to pilot burner.
b) If flame is not sensedwithin 90 seconds, igniter and gas flow are deactivated, blower will post purgeand
control LED flashes 6 times with 3 second pause.
6
Main Burner Ignition
After pilot flame issensed, gas control activates main valve for main burner ignition. The gas control will ignore
flame and pressure switchsignals for 3 seconds allowing for main burner to stabilize.
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