Bx16TRS Radiator Fan switch.

[bx16trs]

Hi all - anybody know the Citroen part number for the BX16TRS rad fan switch, pse?
TIA
Brian

[white exec]

Hi Brian,

Citroen pt.no. is 1264 17, but NFP.
Operating temperatures shown as 87/83 & 92/88 degC.

Choice of 8 (!) makes on Mister Auto, including Valeo, FAE and Vernet.
Spec for each one is listed.
I'm using the FAE 37800 here.

If Mister Auto is not yet re-functioning in the UK, try Autodoc, who do much the same range of products.

Hope helpful.

[bx16trs]

Chris, many many thanks for the info. Just as a double check, is it the 2 or 3 terminal layout, pse? I see that they both seem to be offered for the 1.6 BX.
Brian

[white exec]

It'll be the 3-terminal one, to switch in Low speed fans, followed by High.

Low speed cuts in at 87C and cuts out at 83.
High speed comes in at 92C, and reverts to Low at 88.

The terminals parallel to each other are Low and High, and the one on its own is connected to Ground/chassis.
Low switches to Gnd first, followed by High AS WELL - not either/or, but both Gnd'd for High speed.

[bx16trs]

As far as I can see there is only one electric fan (right hand end of the front plastic grill). Are there generally two fans or does one fan operate at two speeds depending on sensor temperature?
Brian

[Jaba]

As far as I can see there is only one electric fan (right hand end of the front plastic grill). Are there generally two fans or does one fan operate at two speeds depending on sensor temperature?
Brian

Yes you have got it. There is an in line resistor for low speed running.
Out of interest what makes you think the thermostat needs replacing. They seldom fail but do show some temperature drift with age which can be tested with the stat in a pan on the hob with a thermometer.

[white exec]

Haynes has the circuit diagram for the car's fan system.
The Low switch connects the fan to Gnd via a resistor; the High switch connects it directly to Gnd to give the higher speed.

If High speed works, but Low doesn't, it's not unknown for the dropper resistor to have burnt out - or for there to be a corroded connection somewhere.

If you pull the plug on the thermo-switch, IGN on, if you Gnd one of the "parallel" sockets on the connector one should bring on Low speed, the other High. Both Gnd'd should also produce High speed.

[bx16trs]

Thanks guys - really appreciate your thoughts.
OK - here is the problem. The BX sits unloved for weeks at a time (usually 8-ish). Each time I visit I run it up and do a small drive to give it an airing, check the suspension pumps up, look for leaks (!) etc. I ALWAYS wait for it to reach temperature and see if the fan kicks in. This time I started it and left it running, the fan didn't start and coolant eventually spewed out from the rad cap - overheated, therefore.
My diagnosis - rad fan thermal switch or the fan itself. Didn't have time to do the obvious (ground the connector active terminals to see if the fan starts with ign on) so next visit it makes no sense NOT to have the right thermal switch with me, just in case!
Brian

[Jaba]

OK consider this. There are two thermostats in the rad switch. If one fails then the other will still switch the fan. It is most likely to be a simple connection problem at the fan as the connectors are at the front of the car behind the bumper and they do corrode as does the rad thermostat connector.
Easily checked as Chris has outlined at the 3 way connector. If no joy check F4 or use a meter to look for 12v first with ignition on. Does the fan spin by hand, it might be seized.

[bx16trs]

Hadn't thought of terminal/connector corrosion and you may well have hit the nail on the head! As you say, seems unlikely that both sensors in the thermal switch have failed together - although it is original 1986! I did check the fan and it turned ok - no stiffness.
Right - next visit and I will give the suggestions a whirl.
Many thanks indeed, guys.
Brian

[bx16trs]

A belated update! First visit to the Bx since last post (!) so did the investigation. The Fan motored-up fast/slow with the ignition on and the appropriate rad plug terminals connected together. Therefore fan & fan relay working ok (tick) and no blown fuse. Gave the spade terminals on the rad sensor a light sanding, put back the plug a couple of times to achieve decent contact and started. Car ran up to temperature - fan kicked in! Success and very cheap ( now have a spare rad sensor - just in case, as the existing one is the 1986 original)
Thanks again for all the insights.
Brian

[saintjamesy89]

Sorry to hi-jack the thread, but can I ask if cars with twin fans have a different fan switch to those with just one? IIRC they do.

[Jaba]

Sorry to hi-jack the thread, but can I ask if cars with twin fans have a different fan switch to those with just one? IIRC they do.

False memory syndrome. Its the same switch for both.

[saintjamesy89]

Awesome, thanks John.