Combustion air fan
Check the resistance of the combustion air fan motor.Approximately 1 Ohm. Check the current to the combustion air fan by connecting 18 volts across pins 1 and 4. Measure the current after 40 seconds. Current >10 Ampere, renew the combustion air fan. Current <10 Ampere, renew the control unit. Check that the fan wheel is not trapped or jammed. Check the power to the combustion air fan sensor. Measuring points 5 and 10 in the connector for the auxiliary heater control unit. 8 V. Renew the control unit if the value is not correct. Check the power to the combustion air fan sensor with the combustion air fan running. Measuring points 5 and 13 in the connector for the auxiliary heater control unit Average value 4 +/- 0.3 V. Renew the combustion air fan if the value is not correct.
What you'll see
No driver-visible symptom recorded.
System reaction
No system-reaction text recorded.
Diagnostic depth
The combustion air fan does not move.
The fan wheel is blocked, the fan wheel is turning too quickly, or the magnet is missing from the fan wheel.