Service Manual

Sequence of Operation
Abnormal Operation (cont.)
3. Pressure Switch/Blower Temperature Fault:
a) Pressure switch closed at start of call for heat - Thegas controlwaits four seconds then, proceeds to flash
2 times with 3 second pause.The controlwaits 2 minutes and then turns on blower for 30seconds. Theblower
turns off after 30seconds and the controlwaits for pressure switch to open. Any time the Pressure switch
opens,
theblower turns on (or stays on) and the control proceeds to wait for pressure switch to close.
b) Pressure switch or blower temperature switch failed open - Thegas control runs theblower for 30seconds
waiting for the pressure switch and/or blower temperature switch to close.If either sw
itch does not closein30
seconds,theblower turns off and the control flashes 3 times with 3 second pause.Thegas controlwaits two
minutes before turning on theblower for another 30seconds to see the circuit close.This cycle repeats aslong as
there is acall for heat or
until the circuit closes.
c) Pressure switch or blower temperature switch opens during burner operation - Thegas control turns off the
pilot and main valve, runs blower for 15seconds (inter-purge) waiting for pressure switch and/or blower
temperature switch to close.If either switch fails to close, th
e control proceeds as described in 3b above.Ifthe
circuit closes again by the end of the inter-purge, the recyclecounter is incremented, if the recyclecount has
not reached itslimit (4), another trial for ignition begins. Ifthe recyclecount has been reached, thegas control
turns off theblower and flashes 6 times then 2 times with 3 second paus
e.Thegas controlwaits5minutes before
repeating ignition sequence.
4. Trial For Ignition Fault:
a) Pressure switch opens during trial - Thegas control turns off igniter and pilot valve.Thegas control proceeds
as described in 3b above.Ifthe pressure switch closeswithin 30seconds thegas controlwill continue with trial for
ignition starting at blower pre-purge.
b) Flame Not Sensed - Thegas control energizes the s
park igniter attempting to lightthepilot and prove flame.If
flame is not sensed within 90seconds,the igniter turns off, thepilot valve is closed and thegas control runs the
blower through postpurge and flashes 6 times then once with 3 second pause.The controlwaits5minutes before
repeating the ignition sequence.
5. Flame Sensing Fault:
b) Flame lost during run - Thegas control turns off pilot and main valves,runs blower for 15seconds (inter purge).
Thegas control increments the recyclecount, if the recyclecount has not reached itslimit (4), another trial for
ignition begins. Ifthe recyclecount has been reached, thegas control turns off theblower and fla
shes 6 times
then 3 times with 3 second pause.Thegas controlwaits5minutes before repeating the ignition sequence.
c) Flame sensed out of sequence - thegas control only looks for pilot flame when theblower is running.Ifflame is
present when thepilot valve is not open, thegas control proceeds to wait for flame loss
and flashes 5 times with 3
second pause.This continuesuntil flame islost, once theflame signal islost, the control flashes 6 times then 4
times with 3 second pause.The controlwaits5minutes before repeating the ignition sequence.
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