CitroJim wrote: 15 Jul 2015, 16:42
Although you checked the continuity of the Bitron (brown) sensor wiring back to the ECU, have you tried flexing the wires? It sounds like it may all be a bit intermittent there...
It's a failsafe that if the Bitron goes open-circuit the fans will run at full speed. It's always a good fan test to disconnect the Bitron and see they do..
If no indeterminacy can be found in the wiring then I'd be temped to swap the ECU...
So if you disconnect the brown plug and the fans dont fire up , what is the problem ?
The two fans are switched by the cluster of three relays.
Relays are standard automotive 30A/40A type, 5-pin, with one set of changeover (SPDT) contacts.
All three relays are identical.
The relays are interconnected, and all three must be working properly for the system to work as it should.
For slow speed (which should come on as soon as the AC is switched on), the two fans are connected in series.
For high speed, the fans operate in parallel.
There are just two "input" cables (from the Bitron box or temperature controller to the relay cluster): one signals slow speed, the other signals high speed.
The circuit diagram should allow you to identify these two connections, and to test the fan bank at both speeds.
It isn't suffcient to just clean up the three relays' base contacts. They will need opening up, and the contacts inside checked and cleaned. If in doubt, simply replace the set of three with new. They have a hard life in normal service, due to the high current they have to switch, and the weather they have to put up with.
The relay sockets can also corrode. Clean up with some contact cleaner and a slivver of glasspaper.
white exec wrote: 23 Dec 2017, 12:58
At both speeds?
No, not 100% but if they run normally on slow then two out of the three are OK and the fans should start and run OK when needed for cooling.
The Bitron going open/circuit will cause the fail-safe to kick in and cause the fans to run at high-speed. That's why disconnecting the Bitron is a good test of the system too...
When you say disconnecting the Bitron you mean the brown plug on the thermo housing ? This does nothing, the only way I can get the fans to run is shorting the 2 wires on the a/c drier bottle, I have rigged a temporary switch for doing this manually for round town driving, untill I can get this sorted.
kiwifrog wrote: 23 Dec 2017, 20:54
When you say disconnecting the Bitron you mean the brown plug on the thermo housing ?
yes, exactly... Given you can make them run by shorting the 2 wires on the a/c drier bottle shows most of the system is working... You now need to establish why disconnecting the brown plug does not do as expected...
kiwifrog wrote: 24 Dec 2017, 09:07
Do you know where that ECU is located on a mk 1 ?
Under the offside headlamp... It's not easy to get to at all..
I'm just having a thought here... Very early MK1s used a different cooling fan control/aircon arrangement... Yours may be one of those...
So, to save you a lot of unnecessary/fruitless work and wild goosechases please advise your RP number and I'll check - as far as I can - the wiring diagrams applicable to your RP and see what I can dig up...
It may be a few days with the festivities now upon us but sit tight and we'll get this sorted between us all...
