Radiator fan diagnosis

ActivaV6uk · Post by **ActivaV6uk** » 07 Apr 2005, 18:36

if its a bitron unit you need i'm sure i can sorce one localy for you.
if we pay more than £10 for it i would be suprised...
Andy

Post by **RichardW** » 07 Apr 2005, 19:57

"Well, I pulled the brown plug - and nothing happened. No fans, no lights. "
Well that's my understanding well and truly torpedoed then - perhaps the Bitron does not control the lights and doesn't go into limp home mode of full fans if it loses the temperature signal (or maybe yours is just Kaput. Or missing!). Perhaps I need to pull the plug on my own car to see what happens...

tomsheppard · Post by **tomsheppard** » 07 Apr 2005, 20:24

Working aircon and fans would be easy with BX bits. Just the control systems need to be constructed and wired in. Not, perhaps a job for the beginner, but definitely do-able.
If you need a Bitron box, they are about £80 new which for a working engine and aircon sounds like good value to me.

D.Slatford · Post by **D.Slatford** » 07 Apr 2005, 20:29

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by RichardW
Perhaps I need to pull the plug on my own car to see what happens...
<hr height="1" noshade id="quote"></blockquote id="quote">
I'd be interested to know what happens if you do!
Having now seen real schematics, it seems the temperature gauge is run by the bitron unit (assuming that was the bitron unit, there seem to be two units involved, AC control and engine fan control units which I'm taking to mean bitron). This therefore at least partialy works, so it's powered and doing something. The control box is really the only common link between the two fans however, I find it curious they should both fail - unless there really is two faults, such as two relays, two fan motors, or an unlucky combination.

tomsheppard · Post by **tomsheppard** » 07 Apr 2005, 20:43

one relay, if it fails, can kill power to both fans. The simple way of fault finding would be to measure voltage on both sides of the fan with the aircon switched on. Fans at slow speed are wired in series so any break in continuity causes BOTH to fail. Should you find 12 Volts on any fan terminal, ground the other one to test the fan itself.It will runat full speed. You'll do no harm. Something else to consider if you want a cheap way out is to disconnect both fans completely and rewire them through their own switch in parallel to be operated manually. That will at least save you an engine, while you track down the fault.

AndyP · Post by **AndyP** » 08 Apr 2005, 02:56

I had a similar problem and it turned out that the little plastic cover over the relays (just behind the front grille in full blast of wind & rain) had gone awol, all three relays had filled up with water & rusted solid. Three new relay and a plastic bag covering the box and I'm back in business.

alan s · Post by **alan s** » 08 Apr 2005, 03:02

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by D.Slatford

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by RichardW
Perhaps I need to pull the plug on my own car to see what happens...
<hr height="1" noshade id="quote"></blockquote id="quote">
The control box is really the only common link between the two fans however, I find it curious they should both fail - unless there really is two faults, such as two relays, two fan motors, or an unlucky combination.
<hr height="1" noshade id="quote"></blockquote id="quote">
It's not hard to understand as I discovered.
These fans have carbon brushes in them and work in tandem, so both have done identical amounts of work.
Now, they aren't both going to wear out simultaneously and they don't, but what happens is that one will have worn down the brushes to the point where it only works intermittently; something the driver is unaware of until after the event (occasionally noting the temperature is slightly higher than normal and this suddenly seems to 'self correct') and occasionally noticing that the fan(s) appear to be on high speed for no specific reason usually as you stop on a hot day with the air/con operating.
This is caused by the HP switch cutting in due to lack of air flow over the condensor and the safety switch using the fan(s) to reduce the pressure. All of this causes the second fan to do double the work until one day, the second fan also begins to work intermittently.
Remember, when both Space Shuttles failed, it wasn't something complicated that caused the failures; an "O" ring on one and tiles on the other which is why the most obvious and simplest things should be the first to get the attention otherwise you'll drive yourself insane trying to find a fault that doesn't exist.
Alan S

Post by **RichardW** » 08 Apr 2005, 23:25

Well I tried it - pulled the brown connector off, and was met by a vertible gale as both fans roared into full speed - even though the ignition was off. Shoved it back on and the fans stayed on, er.... switched on the ignition and they went off again. Phew[B)]
Tried to refit the spring clip but lost it (probably in the clutch housing!).
Interestingly mine (97 TD with climate control, but without the engine ecu) has the green sensor at the back of the stat housing as well, which I guess feeds into the air-con ECU - which is different, I now realise, to the Bitron, which only seems to control the fans (too busy parping it when the fans didn't go off to remember to look and see if the warning lights were on...!).

Post by **RichardW** » 11 Apr 2005, 13:09

More observations from the land of Bitron... It seems that the bitron brings the cooling fans on at a much lower temp than the radiator switch in the pre-bitron cars, and once on they appear to stay on until you stop the engine. Noticed tha fans spooling down when I stopped in Glasgow on Saturday after pootling around for a bit looking for a parking place - temp had only just gone past 80°C (shouldn't play with connectors for Bitron sensor - makes one paranoid!). Probably explains why I though this car runs cooler in taffic etc than my previous one.

davek-uk · Post by **davek-uk** » 11 Apr 2005, 18:12

I've never had my fans running high speed as far as I know as I haven't tried to disconnect the brown connector. The following observations may be of use:
My fans will run whenever the A/C is switched on or, if the A/C is off, when the engine temperature reached a predefined limit - then the fans will come on and then switch off again when they have reduced the temperature by 5 degrees or so. Acording to the temp gauge, they switch on at 85°C and back off at 80°C while normal running temperature is 75-80°C.
I assume the temp gauge is reading a few degrees under as the temperature goes up to about 81°C before the thermostat opens (83°C) at the start of a journey - whereupon the temperature drops to 75°C.
The car is a 1997, A/C, climate control, Briton, 1.9TD.