32
LDAP-IOM (01-22) 207733-A
Table 15. Operating Sequence (Abnormal Heat Cycle)
Abnormal
Function
Condition
Action
Interrupted
thermostat
call for heat
Thermostat demand for heat is
removed before flame is recognized
Control runs heat section and main venter motors for post-purge period
All outputs are deenergized
Thermostat demand for heat is
removed after successful ignition
Control de-energizes gas valve
Control runs venter motors through post-purge period
Control runs fan motor on heat speed for selected delay OFF time
Ignition retry
Flame is not established on first trial
for ignition period
Control de-energizes gas valve
Venter motors remain energized for 10-second inter-purge period
Spark and gas valve are re-energized
Control initiates another trial for ignition
Flame is not established on second
trial for ignition
Control de-energizes gas valve and runs fan motor on heat speed
Venter motors remain energized
Fan motor deenergizes after 120 seconds and spark and gas valve are re-energized
Control initiates another trial for ignition (this fan delay is self-healing feature for open
auxiliary limit switch)
Flame is not established on third trial
for ignition
Control de-energizes gas valve
Venter motors remain energized for 10-second inter-purge period
Spark and gas valve are re-energized
Control initiates another trial for ignition
Flame is not established on fourth trial
for ignition (initial try plus three re-tries)
Control de-energizes gas valve and proceeds to lockout
Green LED on circuit board flashes once to indicate ignition failure lockout
Limit switch
operation
*
Auto-reset and manual-reset high
temperature limit switches are open
and call for heat is present
Control de-energizes gas valve
Control energizes venter motors and fan motor on heat speed
Limit switches re-close or call for heat
is not present
Control runs venter motors through post-purge period
Control runs fan motor on heat speed through selected delay OFF period before
returning to normal operation
Pressure
switch
operation
Heat section or flue collection box
section pressure switch opens before
trial for ignition period
Venter motors run through 2-second pressure switch recognition delay
Control de-energizes gas valve
Control runs venter motors through post-purge period
Control restarts heat cycle at pressure switch proving state if call for heat still exists
Either pressure switch opens for less
than 2 seconds during trial for ignition
period (shall not interrupt heat cycle)
Control de-energizes gas valve while pressure switches are open
Either pressure switch opens after
successful ignition
Control de-energizes gas valve
Flame is lost before end of 2-second
pressure switch recognition delay
Control responds to loss of flame
Pressure switch(s) remains open for 2
seconds and flame remains
Control deenergizes gas valve
Control runs venter motors through post-purge period
Control runs fan motor on heat speed through selected delay OFF period
When fan OFF delay ends, fan motor is de-energized and heat cycle begins if call for
heat still exists
Continuous
fan operation
Thermostat calls for continuous fan (G)
without call for heat
Fan motor is energized after 0 .25-second delay (this brief ON delay allows terminal
G to energize slightly before terminal Y and allows external changeover relay to
switch from terminal G to terminal W without causing momentary glitches in fan
output
Fan remains energized as long as call for fan remains without call for heat
Thermostat calls for heat (W) during
continuous fan operation
Fan is de-energized
Call for fan is ignored during lockout
*
The limit switch is ignored unless a call for heat is present (terminal W energized) .
OPERATION—CONTINUED
Operating Sequences—Continued
