Xantia Bitron fault?

[Old-Guy]

Remote diagnosis of another problem with the (2.1 TD S1) VSX, please. The radiator fans don't come on when the engine gets hot off if the A/C is off. Switch on the A/C, and the fans run at slow speed regardless of engine temperature - as I understand they should? So is this a problem with the Bitron or with the temperature sender? If the latter (which has supposedly been replaced fairly recently), which one (on the fuel filter base) is it?

[xantia_v6]

The fan temperature sensor is the brown one. If you disconnect it, the fans should run at full speed regardless of A/C setting.
It is common to have a problem with the 3 fan relays in front of the radiator.

[Old-Guy]

The fan temperature sensor is the brown one. If you disconnect it, the fans should run at full speed regardless of A/C setting.
It is common to have a problem with the 3 fan relays in front of the radiator.

Brilliant, I'll try that in the morning. How do I get at those relays please? (What a place to put a trio of relays - exposed to maximum salt spray )

[spider]

Same on the 406. Fun to get to.

Sounds obvious but remember they are permanent live so watch your fingers as they might start up anytime when you're in the area. Fingers + Fans = not good news as they are quite powerful.

Yes unplugging the sensor should bring them on , does seem to vary I think slow speed for a few seconds then higher speed.

One relay for each fan I think and the overheat / fault one (this causes them to run when unplugged)

I sort of expect you'll find them corroded or the contact sockets corroded, should be a straighforward fix though.

There is a control unit for these (on a 406 at least) but I don't know where it is on a Xantia, on a 406 its usually tucked up behind the glovebox (reachable from footwell area) on a RHD car.

[Stewart(oily)]

I found a Bitron unit on my S2 behind the front bumper on the passenger side, below the headlight.

[Mandrake]

The Bitron was also below the left hand headlight on my 1997 2 litre petrol Series 1 Xantia, it looks like an engine ECU double injection relay with the sliding clip connector, and mind was more or less hanging from the cable with a clip holding the cable. On that car the fans would intermittently kick into high speed accompanied by the temperature warning light even when the engine was cold, cleaning the connector with contact cleaner fixed it.

[Mandrake]

Sounds obvious but remember they are permanent live so watch your fingers as they might start up anytime when you're in the area. Fingers + Fans = not good news as they are quite powerful.

Never mind "watching your fingers", don't put your fingers anywhere near the fans without first disconnecting the battery!

The fans can indeed come on even when the ignition is off and the car is locked, particularly in the case of a faulty bitron. Generally any condition that would cause the high fan speed when the ignition is on will trigger the low fan speed when the ignition is off.

[Old-Guy]

Thanks for the safety warnings! A few years ago, an acquaintance nearly lost his fingers to a ME109 that 'spat back' as he swung the prop.