The fans are controlled by a radiator mounted temperature sensor and other
devices. For a 95 XJR, the “Fan Control Relay Module” (located underneath
the driver’s side headlight area) has multiple inputs. These fans are
supposed to operate with the engine off if the coolant temperature is high.
They will continue to run until the coolant temperature drops below the
radiator thermal switch setpoint.
The fans run in series (electrically) with approximately 6 VDC applied to
each motor (low speed) when the radiator mounted thermal switch setpoint of
88 deg. C is reached. When the coolant reaches 100 deg. C, the fans are
configured in parallel (electrically) with approximately 12 VDC supplied to
each motor (high speed).
Both fans are also controlled by the refrigerant pressure switches (both the
triple switch and the single switch). Apparently, the triple switch
performs the following functions:
Allows the air conditioning compressor to operate if the system pressure
is greater than 2 bars.
Opens the compressor circuit if the system pressure is greater than 27
Places the radiator fans in parallel operation (high speed) if the
system pressure is greater than 20 bars.
The single refrigerant pressure switch places the fans in series operation
(low speed) if the system pressure is greater than 12 bars.
For troubleshooting, I would disconnect the both refrigerant pressure
switches so that they have no impact upon fan operation.
If the fans operate in either speed with the engine cold, there’s a need for
Disconnect the radiator thermal switch (lower driver’s side of
radiator). If the fan stops, then the problem is the switch.
If the fans do not stop, its likely the Fan Control Relay Module is
stuck in either the high or low position.
If its the switch … replace it. If its the Fan Control Relay Module, try
to open it and clean the contacts. If this is not feasible, replace it.