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HEATING
FURNACE CONTROL
TERMS
Commonly Used Furnace Control Terms
Auto Reset: If shutoff occurs, the control delays for a specific recycle delay period before beginning another trial for ignition (models with
retries only).
Continuous: An ignition source which, once placed in operation, is intended to remain ignited or energized continuously until manually
interrupted.
Cool Delay to Fan Off: Timing to allow the fan to run after the call for cool ends. This allows residual cooling capacity to be removed from the
cooling coils and distributed to the conditioned space.
Cool Delay to Fan On: Timing to allow the cooling coils to cool off before turning on the fan.
Flame Failure Re-ignition Time: “The period of time between loss of the supervised ignition source or the supervised main burner flame and
a re-ignition attempt. During this time period the main burner gas supply is not shut off.”
Flame Failure Response Time: “The period of time between loss of the supervised ignition source or the supervised main burner flame and
the action to shut off the gas supply.”
Flame-Establishing Period: “The period of time between initiation of gas flow and proof of the supervised flame or between the proof of
supervised flame and initiation of gas flow. This may be applicable to proof of the ignition source or main burner flame, or both.”
Heat Delay to Fan Off: Timing to allow the fan to run after the call for heat ends. This allows residual heat to be removed from the heat
exchanger and distributed to the conditioned space.
Heat Delay to Fan On: Timing to allow the heat to build up in the plenum before turning on the fan.
Ignition Activation Period: The period of time between energizing the main gas valve and deactivation of the ignition means prior to the
lockout time.
Initial Ignitor Warm-Up: Duration of ignitor warm-up time on the first 64 attempts.
Integrated: Has a microprocessor which monitors and analysis the operation of the continually MV, ignitor, inducer, fan, flame sensor, but it
also turns on the humidifier, and air cleaner if those are available in the house. In other words it incorporates the all operations connected to
the furnace from one power source.
Intermittent: “An ignition source which is automatically ignited or energized when the equipment is called on to operate and which remains
continuously ignited or energized during each period of main burner operation. The ignition source is automatically extinguished or deener-
gized when each main burner operating cycle is completed.”
Intermittent/Continuous: “An ignition source which is ignited or energized upon equipment user initiation of the operation cycle and which
remains continuously ignited or energized during the equipment use cycle. The ignition source is extinguished or de-energized when the
equipment use cycle is completed.”
Intermittent/Interrupted: “An ignition source which is ignited or energized upon equipment user initiation of the operational cycle and which is
extinguished or de-energized after the equipment use cycle has been initiated.”
Inter-Purge: Period between trials for ignition when both the gas valve and ignition source are deactivated to allow unburned gas to escape
before the next trial.
Interrupted: “An ignition source which is automatically ignited or energized when the equipment is called on to operate and which remains
ignited or energized during the main burner Flame-Establishing Period. The ignition source is automatically extinguished or deenergized when
each main burner Flame-Establishing Period is completed.”
Lockout Time: The period of time between initiation of gas flow and the action to shut off the gas flow in the event of failure to establish proof
of the supervised ignition source or the supervised main burner flame. Reinitiating the lighting sequence requires a manual operation.
Non-Integrated: Only controls or sends a signal to the ignitor and the mv and monitor the flame sensor
Post-Purge: “After all ignition cycles are complete, the control will enter post-purge. The combustion fan will remain on to allow unburned gas
to escape. After post-purge is complete, the combustion fan will turn off. “
Pre-Purge: Initial time delay between thermostat contact closure and trial for ignition.
Re-cycle: Flame is sensed and then lost causing the control to re-cycle.
Recycle Time: “The period of time between shutoff of the gas supply following loss of the supervised ignition source or the supervised main
burner flame and reactivation of the ignition source.”
Retries: Additional ignition attempts if the original ignition attempt is unsuccessful.
Retry Ignitor Warm-Up: Duration of ignitor warm-up time if the control retries.
Trial for Ignition: Period during which the valve and ignition source is activated, attempting to ignite gas at the burner.
Valve Sequence Period: Valve sequence period is the cumulative total amount of time that the gas valve is energized before entering lockout.
Model(s) . Page(s)
36C............................................................................... .172 – 175
36E............................................................................... 176
36H............................................................................... 177
36G/J............................................................................ 178
21M51U-843................................................................. .179 – 180
21V51U-843.................................................................. .181 – 182
50A55-843.................................................................... .183 – 184
HEATING 171
Model(s) Page(s)
50A65-843........................................................................ 185 – 186
50E47-843........................................................................ 187 – 188
50D50............................................................................... 189
50M56U............................................................................ . 190 – 192
24A01/24A05.................................................................... 193
3L09.................................................................................. . 194 – 196
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TECHNICAL HELP