Intake Air Heater: Description and Operation

Air Intake Heater Relays:

The air intake heater system uses relays and heaters, controlled by the control module, to preheat the air before it enters the combustion chamber. The relays purpose is to ENERGIZE the air intake heaters so that they can warm the incoming air as it enters the intake manifold. The air intake heaters can be ENERGIZED before and/or after engine cranking, depending upon the intake manifold air temperature. The control module receives a signal from the thermistor that indicates the air intake temperature. If the air intake temperature is at or below 59~F (15~C) the control module will start the air intake preheat or post-heat cycle.



PREHEAT CYCLE

The air intake preheat cycle will start if the following conditions exist:
^ The ignition switch in in the ON position.
^ The control module has not received a crank signal.
^ The air intake temperature is at or below 59~F (15~C).

If the preheat cycle is started, the control module will illuminate the Wait-To-Start lamp. Once the preheat cycle has finished, the Wait-To-Start lamp will go out, and the engine can be started.

If the control module receives an engine crank signal while the preheat cycle is running, the air intake relays will be DE-ENERGIZED causing the preheat cycle to be aborted.



POST-HEAT CYCLE

The air intake post-heat cycle will begin if the following conditions exist:
^ The engine has been started and is running.
^ The air intake temperature is at or below 59~F (15~C) when the ignition switch was turned ON.

The intake air heaters have two different modes of operation depending upon the intake manifold air temperature, either both heaters are ENERGIZED or they are cycled ON and OFF individually (while one is ENERGIZED the other is not and vice versa). The amount of time that the air intake heaters remain ENERGIZED depends upon the intake manifold air temperature.