Reznor MAPS III, Cabinet D RECB Users Manual User Manual
Page 28
Form O-MAPSIII Cabinet D, P/N 222918R9, Page 28
4. Gas Heat
Section
Maintenance
(cont'd)
4.2 Heat Section
Controls
(cont'd)
Ignition Controller on Non-Modulating Gas-Fired Furnace on
MAPS D Sizes 1000, 1200, 1400, or 1600 with Two Furnaces
(cont'd)
4.2.2 Ignition System
(cont'd)
Normal Heat Cycle Operating Sequence - Non-Modulating Furnace
of D Cabinet with Size 1000, 1200, 1400, or 1600 Heat Section
1) Call for Heat - The heating/cooling system controller calls for heat. The ignition sys-
tem circuit board checks to see that the limit switch is closed and the pressure switch is
open. If the limit switch is open, the circuit board responds as defined in the “Abnormal
Heat Cycle, Limit Switch Operation”. If the pressure switch is closed, the circuit board
will do four flashes on the green LED and wait indefinitely for the pressure switch to
open. If the pressure switch is open, the circuit board proceeds to prepurge.
2) Prepurge - The circuit board energizes the venter motor and waits for the pressure
switch to close. If the pressure switch does not close within 30 seconds of the venter
motor energizing, the circuit board will do two flashes on the green LED. The circuit
board will leave the venter motor energized indefinitely as long as the call for heat
remains and the pressure switch is open.
When the pressure switch is proven closed, the circuit board 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 circuit board responds as defined in “Fault
Modes, Undesired Flame”.
The ignition system circuit board runs the venter motor for a 20 second prepurge time,
then proceeds to the ignition trial period.
3) Ignition Trial Period - The ignition system circuit board energizes the spark and
main gas valve. The venter remains energized. If flame is sensed at the burner during
the first 16 seconds, the spark is de-energized. 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 specified in “Abnormal Heat Cycle, Ignition Retry”. If flame is
present, the circuit board proceeds to steady heat.
4) Steady Heat - Circuit board inputs are continuously monitored to ensure limit and
pressure switches are closed, flame is established, and the system controller call for
heat remains. When the call for heat is removed, the ignition system circuit board de-
energizes the gas valve and begins postpurge timing.
5) Post Purge - The venter motor output remains on for a 45 second postpurge period
after the system controller is satisfied.
Abnormal Heat Cycle
Functions - Non-
Modulating Furnace
of D Cabinet with Size
1000, 1200, 1400, or
1600 Heat Section
Interrupted Call for Heat - If the system controller call for heat is removed before the
flame is recognized, the circuit board will run the venter motor for the post purge period
and de-energize all outputs.
If the call for heat is removed after successful ignition, the circuit board will de-energize
the gas valve and run the venter motor through post purge.
Ignition Retry - If flame is not established on the 1st trial for ignition period, the igni-
tion system circuit board de-energizes the gas valve, and the venter motor remains
energized for an inter-purge period of 10 seconds. The spark and gas valve are then
re-energized, and the circuit board initiates a 2nd trial for ignition.
If flame is not established on the 2nd trial for ignition, the circuit board de-energizes
the gas valve and venter motor remains energized. The spark and gas valve are re-
energized and the circuit board initiates a 3rd trial for ignition.
If flame is not established on the 3rd trial for ignition period, the circuit board de-ener-
gizes the gas valve, and the venter motor remains energized for an inter-purge period
of 10 seconds. The circuit board then re-energizes the gas valve and spark and initi-
ates a 4th trial for ignition.
Do not attempt to disassemble the control module. However, each heating season
check the lead wires for insulation deterioration and good connections.
Proper operation of the direct spark ignition system requires a minimum flame signal of
1.0 microamps as measured by a microampmeter.