Planning the next
AO Silver Member
Join Date: May 2007
Location: United Kingdom
The aircon system monitors the pressure of the refrigerant. The higher the pressure, the more cooling that is needed. A pressure switch between the air filter housing and the radiator does the work. At low pressure, no radiator fan, at medium pressure the fans should be on low speed, at high pressure fans at high speed. Over maximum pressure, the fans will be on high speed and the aircon compressor clutch will disengage.
This is why I asked if the aircon works. If the aircon compressor clutch does not engage it may be that the pressure switch has failed on over pressure causing the fans to operate permanently on high speed. You can easily prove that by disconnecting the plug from the pressure switch and the fans should then stop if the pressure sensor is faulty.