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STEP # STEP #
1) Thermostat calls for heat. 8) Continued...
2) Combustion fan turns on. return to Step 2. If after 3 attempts
3) Pressure switch closes. malfunction still occurs, furnace will
4) Power to Ignitor. go into lockout mode for one hour.
5) Ignitor warm up period. This one hour mode can be bypassed
6) Gas flow to burner. by resetting thermostat.
7) Burner ignition proven. 9) Thermostat satisfied.
8) Circulating blower on. 10) Gas valve closes.
NOTE: If there is a mal- 11) Combustion fan off.
function in any of the 12) Blower off.
above steps, the sequence
will stop at that point and HEATER NOW IN STAND-BY MODE.
Page 13
SEQUENCE OF OPERATION - HEDV403/4
Lockout
t=10 sec.
IGNITION
PROVED?
YES
t=50 sec.
NO
Blower
On
@t=X
Thermostat
is satisfied
t=x sec.
Burners
Off
t=X+15 sec.
Combust.
Fan Off
Blower
Off
@t=0
THERMOSTAT
CALLS FOR
HEAT
Power to
Combust.
Fan
10 SEC
PURGE
Three
Attempts
Made?
NO
YES
Fan
Proved
YES
NO
Power to
Ignitor
NO
Three
Attempts
Made?
YES
Gas
Flow
10 SEC
PURGE
t=X+120 sec.
t=15 sec.
t=20 sec.