Coolant Temperature Control

Coolant temperature control
When the ECU first enters the active mode, it initiates a start to full load combustion. Full load combustion continues until the heat exchanger casing temperature reaches 60 degrees C (140 degrees F), when the ECU decreases the speed of the FBH fuel pump and the combustion air fan to half speed, to produce part load combustion. The ECU maintains part load combustion while the heat exchanger casing temperature remains between 54 and 65 degrees C (129 and 149 degrees F). If the heat exchanger casing temperature decreases to 54 degrees C (129 degrees F), the ECU switches the system to full load combustion again. If the heat exchanger casing temperature increases to 65 degrees C (149 degrees F), the ECU enters a control idle phase of operation.

On entering the control idle phase, the ECU immediately switches the FBH fuel pump off, to stop combustion, and starts a timer for the combustion air fan. After a 2 minute cooldown period, the ECU switches the combustion air fan off and then remains in the control idle phase while the heat exchanger casing temperature remains above 59 degrees C (138 degrees F). If the heat exchanger casing temperature decreases to 59 degrees C (138 degrees F), within 15 minutes of the ECU entering the control idle phase, the ECU initiates a start to part load combustion. If more than 15 minutes elapse before the heat exchanger casing temperature decreases to 59 degrees C (138 degrees F), the ECU initiates a start to full load combustion.

In order to limit the build-up of carbon deposits on the glow plug/flame sensor, the ECU also enters the control idle phase if the continuous part and/or full load combustion time exceeds 72 minutes. After the cooldown period, if the heat exchanger casing is still in the temperature range that requires additional heat, the ECU initiates an immediate restart to part or full load combustion, as appropriate.