Switching Point Temperatures
| ITEM | SWITCHING POINT | TEMPERATURE, °C (°F) |
|---|---|---|
| 1 | Power load to high load | 65 °C (149 °F) |
| 2 | High load to low load | 80 °C (176 °F) |
| 3 | Low load to control idle | 85 °C (185 °F) |
| 4 | Control idle to low load | 75 °C (167 °F) |
| 5 | Low load to high load | 65 °C (149 °F) |
| 6 | High load to power load | 55 °C (131 °F) |
After the start sequence, the FFBHCM maintains power load combustion until the coolant temperature reaches switching point temperature 1. At this temperature, the FFBHCM decreases the speed of the FFBH fuel pump and the combustion air fan to enable high load combustion. The FFBHCM maintains high load combustion while the coolant temperature remains between switching point temperatures 2 and 6. At high load combustion the temperature of the coolant will increase or decrease depending on the amount of heat required to heat the vehicle interior. If the coolant temperature decreases to switching point temperature 6, the FFBHCM increases the speed of the FFBH fuel pump and the combustion air fan to full speed, to return to power load combustion. If the coolant temperature increases to switching point temperature 2, the FFBHCM decreases the speed of the FFBH fuel pump and the combustion air fan to enable low load combustion. At low load combustion the temperature of the coolant will again increase or decrease depending on the amount of heat required to heat the vehicle interior. If the coolant temperature decreases to switching point temperature 5 the FFBHCM increases the speed of the FFBH fuel pump and the combustion air fan to enable high load combustion. If the coolant temperature increases to switching point temperature 3, the FFBHCM enters a control idle phase of operation.
On entering the control idle phase, the FFBHCM immediately switches the FFBH fuel pump off, to stop combustion, and starts a timer for the combustion air fan. After a 90 seconds (diesel vehicles) or 120 seconds (petrol vehicles) cool down period, the FFBHCM switches the combustion air fan off and then remains in the control idle phase while the coolant temperature remains above switching point temperature 4. If the coolant temperature decreases to switching point temperature 4, the FFBHCM initiates a start to low load combustion.