Reznor LDAP Unit Installation Manual - Manual (Page 29)

Form I-LDAP, P/N 207733R6, Page 29
Normal Heat Cycle
Operating Sequence
1) Call for Heat - The thermostat calls for heat by energizing the “W” terminal.
The control checks to see that the limit and high limit switches are closed and
the heat section pressure switch is open and the main combustion air pressure
switch (Sizes 800 and 1200) is open. If the limit or high limit switch is open,
the control responds as defined in the “Abnormal Heat Cycle, Limit Switch
Operation”. If the heat section pressure switch or main combustion air pressure
switch are closed, the control will do four flashes on the green LED and wait
indefinitely for the heat section pressure switch or main combustion air pres-
sure switch to open. If the heat section pressure switch and main combustion
air pressure switch are open, the control proceeds to prepurge.
2) Prepurge - The control energizes the heat section venter motor and main
venter motor (Sizes 800 and 1200) and waits for the heat section pressure
switch and main combustion air pressure switch to close. If the heat section
pressure switch or main combustion air pressure switch does not close within
30 seconds of the heat section venter motor and main venter motor energizing,
the control will do two flashes on the green LED. The control will leave the heat
section venter motor and main venter motor energized indefinitely as long as
the call for heat remains and the heat section pressure switch or main combus-
tion air pressure switch is open.
When the heat section pressure switch and main combustion air pressure
switch are proven closed, the control begins the prepurge time. If flame is
present any time while in prepurge, the prepurge time is restarted. If flame is
present long enough to cause lockout, the control responds as defined in “Fault
Modes, Undesired Flame”.
The control runs the heat section venter motor and main venter motor for a 20
second prepurge time, then proceeds to the ignition trial period.
3) Ignition Trial Period - The control energizes the spark and main gas valve.
The venter remains energized. If flame is sensed during the first 16 seconds,
the spark is de-energized and the control proceeds to heat fan on delay. If flame
has not been sensed during the first 16 seconds, the control de-energizes the
spark output and keeps the gas valve energized for an additional one second
flame proving period. If flame is not present after the flame proving period, the
control de-energizes the gas valve and proceeds with ignition re-tries as speci-
fied in “Abnormal Heat Cycle, Ignition Re-try”. If flame is present, the control
proceeds to the fan on delay.
4) Fan On Delay - The control waits for 30 seconds from the time the gas
valve opened and then energizes the fan motor. The gas valve, heat section
venter motor, and main venter motor remain energized. The control proceeds
to steady heat mode.
5) Steady Heat - Control inputs are continuously monitored to ensure limit, high
limit, heat section pressure switch, and main combustion air pressure switch
are closed, flame is established, and the thermostat call for heat remains.
When the thermostat call for heat is removed, the control de-energizes the gas
valve and begins post-purge and fan off delay timing.
6) Post Purge - The heat section venter motor and main venter motor outputs
remain on for a 45 second post-purge period after the thermostat is satisfied.
Interrupted Thermostat Call for Heat - If the thermostat demand for heat is
removed before the flame is recognized, the control will run the heat section
venter motor and main venter motor for the post purge period and de-energize
all outputs.
If the thermostat demand for heat is removed after successful ignition, the con-
trol will de-energize the gas valve, run the heat section venter motor and main
NOTE: All LED Flash
Codes are on page
41.
Abnormal Heat Cycle
Functions