Honeywell PDX450S*F(BN,SX) PDX Series, Sequence of Operation, Trial For Ignition Fault

Sequence of Operation

PDX Series

3. Pressure Switch/Blower Temperature Fault:

a)Pressure switch closed at start of call for heat - The control waits four seconds then, proceeds to flash

2 times with 3 second pause. The control waits 2 minutes and then turns on blower for 30 seconds. The blower turns off after 30 seconds and the control waits for pressure switch to open. Any time the Pressure switch opens, the blower turns on (or stays on) and the control proceeds to waiting for pressure switch to close.

b) Pressure switch or blower temperature switch failed open - The control runs the blower for 30 seconds

waiting for the pressure switch and/or blower temperature switch to close. If either switch does not close in 30 seconds, the blower turns off and the control flashes 3 times with 3 second pause. The control waits two

minutes before turning on the blower for another 30 seconds to see the circuit close. This cycle repeats as long as there is a call for heat or until the circuit closes.

c)Pressure switch or blower temperature switch opens during burner operation - The control turns off the pilot and main valve, runs blower for 15 seconds (inter-purge) waiting for pressure switch and/or blower temperature switch to close. If either switch fails to close, the control proceeds as described in 3b above. If the circuit closes again by the end of the inter-purge, the recycle counter is incremented, if the recycle count has

not reached its limit (4), another trial for ignition begins. If the recycle count has been reached, the control turns off the blower and flashes 6 times then 2 times with 3 second pause. The control waits 5 minutes before

repeating ignition sequence.

4. Trial For Ignition Fault:

a)Pressure switch opens during trial - The control turns off igniter and pilot valve. The gas control proceeds

as described in 3b above. If the pressure switch closes within 30 seconds the gas control will continue with trial for ignition starting at blower pre-purge.

b) Flame Not Sensed - The control energizes the spark igniter attempting to light the pilot and prove flame. If

flame is not sensed within 90 seconds, the igniter turns off, the pilot valve is closed and the gas control runs the

blower through post purge and flashes 6 times then once with 3 second pause. The control waits 5 minutes before repeating the ignition sequence.

5. Flame Sensing Fault:

a)Flame lost during run - The control turns off pilot and main valves, runs blower for 15 seconds (inter purge).

The control increments the recycle count, if the recycle count has not reached its limit (4), another trial for ignition begins. If the recycle count has been reached, the control turns off the blower and flashes 6 times then 3 times with 3 second pause. The control waits 5 minutes before repeating the ignition sequence.

b) Flame sensed out of sequence - the control only looks for pilot flame when the blower is running. If flame is present when the pilot valve is not open, the control proceeds to wait for flame loss and flashes 5 times with 3 second pause. This continues until flame is lost, once the flame signal is lost, the control flashes 6 times then 4 times with 3 second pause. The control waits 5 minutes before repeating the ignition sequence.

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