GT-R Radiator fan set-points

Owned by Lucan Hetherington
Last updated: Aug 20, 2020
2 min read

From our investigations we see the base fan duty is set with coolant temperature and vehicle speed but it will interpolate between these values so at 97 deg C it will be around 60% duty but conditions like AC on / off affect the minimums and maximum that can be set and these are based on the AC pressure sensor output. To break it down

  • The "Radiator Fan Duty" map is the base fan duty for normal operation to keep the engine cool, the axis is vehicle speed and coolant temperature, the output is duty for the two main fan motors

  • The "Radiator Fan Duty Min A/C on" and "Radiator Fan Duty Max A/C on" are the limits imposed by ac system on the main cool cooling system to maintain enough evaporator cooling and the axis of these maps is vehicle speed and evap pressure sensor pressure (Note: it does not interpolate between these values just uses the direct column and rows)

  • The radiator fan #4 appears to be the evaporator threshold values are AC evaporator temperature temperature error (as in deviation from target temperature) and these values set the Radiator fan #4 outputs based on row.

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  • I don't believe there is a separate radiator fan for the ac system so it increases the normal engine cooling fan duty to achieve the airflow required.  

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The radiator fan #4 thresholds values are evaporator temperature error (between target and actual temp) and are not logged so its difficult to be able to tune these but basically if the AC is working hard it will add all of the duty on the last row of Rad Fan 4 map.