Cooling fans on permanently
Discussion
Hi
Chim's been idle for a few weeks, but off out today (what with weather being so nice an' all...) so just drove it out of garage. Strangely, as soon as ignition was switched on the fans started up. Engine was obviously stone cold at this point. They then, as I was going down the drive, switched off for a second and started spooling down twice, only to come back on and stay there.
Clearly this sounds like some sort of bad connection within the controlling circuit - the temp sender at the bottom of the swirl pot has always looked like a dodgy connector, but fiddling with it makes no difference to the fans. Would that going open circuit turn them on or off? I haven't checked the fuse box yet, but since the fans are running very well even when not needed I presume the fuse is ok. Where else should I be looking?
Thanks for any help!
Andrew
Chim's been idle for a few weeks, but off out today (what with weather being so nice an' all...) so just drove it out of garage. Strangely, as soon as ignition was switched on the fans started up. Engine was obviously stone cold at this point. They then, as I was going down the drive, switched off for a second and started spooling down twice, only to come back on and stay there.
Clearly this sounds like some sort of bad connection within the controlling circuit - the temp sender at the bottom of the swirl pot has always looked like a dodgy connector, but fiddling with it makes no difference to the fans. Would that going open circuit turn them on or off? I haven't checked the fuse box yet, but since the fans are running very well even when not needed I presume the fuse is ok. Where else should I be looking?
Thanks for any help!
Andrew
andy-w said:
borke otter switch?
Ooh wow is that a specialist extra? Or can I only have it with a borg 'box?
sorry couldn't resist... Incidentally, I've got a manual fan override switch on the steering wheel cowling. It is very easy to accidentally press!Aubrey
Edited by Aubrey on Sunday 20th January 14:38
Hi Andrew,
Try disconnecting the otter switch connections on the swirl pot.
If the fans stay on then you may have a sticky relay under the dash top, or a short in the otter switch relay wiring.
The otter switch does not drive the fans directly as the curent drawn by the fans is too great at about 20 amps a-piece or there abouts. So there are basically two parts to the fan circuit.
The otter switch which drives the relay coil,(low currect) this then pulls in the two relays one for each fan which then starts the fans.(high current)
You therefore need to determine which circuit is causing the fault before going any further.
Hope this helps.
Paul.
Try disconnecting the otter switch connections on the swirl pot.
If the fans stay on then you may have a sticky relay under the dash top, or a short in the otter switch relay wiring.
The otter switch does not drive the fans directly as the curent drawn by the fans is too great at about 20 amps a-piece or there abouts. So there are basically two parts to the fan circuit.
The otter switch which drives the relay coil,(low currect) this then pulls in the two relays one for each fan which then starts the fans.(high current)
You therefore need to determine which circuit is causing the fault before going any further.
Hope this helps.
Paul.
Thanks guys...
I feared that might be the case - had already pulled off the otter switch wires, and the fans resolutely keep going. Shorted them out for good measure, which clearly made no difference as that would turn them on anyway under normal circumstances. That would seem to isolate the problem to either a short in the wiring to the otter switch (which looks ok as far as where it disappears behind the air con compressor - which could have something to do with it) or as Paul suggests on the other side of the relay.
Of course, the air con has an override which switches on the fans intermittently as it sees fit when it's on (which it isn't...), just to make things more interesting.
I don't have a manual fan override on mine, so sadly it's not that simple :-)
Don't really fancy a dash-off job this afternoon (edited to add: though the fan relays are in the main fusebox, aren't they?), and the bible doesn't say too much about the fan circuitry. H'mmm. Well, at least they're stuck on rather than off, I suppose, though in this weather that's probably overkill...
Anyone think of anything else I should be checking?
Andrew
PS Have heard that the Borke otter switches are not worth the extra outlay. I think TVR power do a twin-otter switch upgrade, using illegal otter switches manufactured in Russia which can fail the MOT, but liberate up to an extra 40 bhp. The otter switch is a big bottleneck in top end power on these engines. I think.
I feared that might be the case - had already pulled off the otter switch wires, and the fans resolutely keep going. Shorted them out for good measure, which clearly made no difference as that would turn them on anyway under normal circumstances. That would seem to isolate the problem to either a short in the wiring to the otter switch (which looks ok as far as where it disappears behind the air con compressor - which could have something to do with it) or as Paul suggests on the other side of the relay.
Of course, the air con has an override which switches on the fans intermittently as it sees fit when it's on (which it isn't...), just to make things more interesting.
I don't have a manual fan override on mine, so sadly it's not that simple :-)
Don't really fancy a dash-off job this afternoon (edited to add: though the fan relays are in the main fusebox, aren't they?), and the bible doesn't say too much about the fan circuitry. H'mmm. Well, at least they're stuck on rather than off, I suppose, though in this weather that's probably overkill...
Anyone think of anything else I should be checking?
Andrew
PS Have heard that the Borke otter switches are not worth the extra outlay. I think TVR power do a twin-otter switch upgrade, using illegal otter switches manufactured in Russia which can fail the MOT, but liberate up to an extra 40 bhp. The otter switch is a big bottleneck in top end power on these engines. I think.
Edited by WooHoo on Sunday 20th January 15:06
Edited by WooHoo on Sunday 20th January 16:08
Right. Well after a bit of footwell-diving, it's now clear that the relay itself is fine. The fans are appropriately deactivated if I pull it out, but come right back on again when I replace it with another (known good) relay. So the problem lies with the low current side of things, which inconveniently includes the air con as Dave mentioned, and about which I know nothing. I figure this is more likely to be the problem than the wires heading to and from the otter switch, because it just being the wires would be too easy and this is a TVR. Should check that, though... Anyone know what I should get at the otter switch end of those wires on a voltmeter? I'm guessing one should be about 12V and the other ground...
The fusebox internally supplies 12v to the control circuit across the relay, you just ground the green/pink wire to activate the power side of the relay and switch on the fans. You have isolated the otter switch, just the over-ride switch and a/c bits to do before you have to start searching for rogue wiring 
Dave
Dave
Just plugged the voltmeter into the otter switch wiring - I'm getting about 4.5V on the pink wire and a good ground on the black. Think this probably means the wiring's ok, as if there was a rogue short to ground on the live side (which would cause these symptoms) I'd expect the voltage there to be zero. 4.5V is pretty low, granted, but given the quality of the wiring such a drop from the fusebox to the switch doesn't surprise me that much.
So the air-con looks increasingly suspect. This problem persists whether it's on or off, but I don't think that tells me much...
Balls.
Andrew
So the air-con looks increasingly suspect. This problem persists whether it's on or off, but I don't think that tells me much...
Balls.
Andrew
WooHoo said:
Just plugged the voltmeter into the otter switch wiring - I'm getting about 4.5V on the pink wire and a good ground on the black. Think this probably means the wiring's ok, as if there was a rogue short to ground on the live side (which would cause these symptoms) I'd expect the voltage there to be zero. 4.5V is pretty low, granted, but given the quality of the wiring such a drop from the fusebox to the switch doesn't surprise me that much.
4.5 V doesn't sound good.If the wire is disconnected from the otter switch you should see a solid battery voltage here. If it's connected to the switch then you should see battery voltage when the switch is open (cold) and earth when it is closed (hot).
Hi there.
As you suspect the A/C does use the radiator fans to cool the A/C condenser that sits infront of the radiator. A thing to check for is that the aircon is not switched on as in some cases this can cause the fans to run as soon as you start the car(only on some systems).
It's most likly that the Trinary switch that sits on the reciever/drier (n/s infront of the condenser may be at fault, or with the slight voltage at the otter switch you may have corroded connections on the trinary switch causing the fan relay to pull in. I see faults like this over the winter with the salt on the roads etc.
Ade
As you suspect the A/C does use the radiator fans to cool the A/C condenser that sits infront of the radiator. A thing to check for is that the aircon is not switched on as in some cases this can cause the fans to run as soon as you start the car(only on some systems).
It's most likly that the Trinary switch that sits on the reciever/drier (n/s infront of the condenser may be at fault, or with the slight voltage at the otter switch you may have corroded connections on the trinary switch causing the fan relay to pull in. I see faults like this over the winter with the salt on the roads etc.
Ade
Thanks Peter and Ade...
I agree that 4.5V is a concern, but I can't work out how a loose connection would cause a stable, low voltage (as in, I'd expect an inappropriate intermittent ground) and wonder if it's just an incidental finding - the air-con could be involved somewhere upstream absorbing some potential (clutching at straws here...).
I drove back to work yesterday as planned, and found that for most of the journey the fans were inappropriately on, then came into town and found that they would switch off, but switch back on after I went over a bump or two (engine still below fan threshold). After a bit of slow driving the engine temp came up, and then the fans were trying to come in but cutting out before they'd spooled up, and then coming in again. Repeatedly. H'mmm. They then stayed on as you'd expect, by which time I didn't know if it was because the engine was warm or because they'd be on anyway as when the problem started. All this stopping and starting will no doubt blow the fuse at some point (I'm on a single 40A), which I'll have to look out for. Think I'll have a look and see if I can find any air-con switches looking corroded - Chim's my only car, so sadly gets taken out in all sorts of grotty conditions road-grit and salt wise...
Fingers crossed, and thanks again!
Andrew
I agree that 4.5V is a concern, but I can't work out how a loose connection would cause a stable, low voltage (as in, I'd expect an inappropriate intermittent ground) and wonder if it's just an incidental finding - the air-con could be involved somewhere upstream absorbing some potential (clutching at straws here...).
I drove back to work yesterday as planned, and found that for most of the journey the fans were inappropriately on, then came into town and found that they would switch off, but switch back on after I went over a bump or two (engine still below fan threshold). After a bit of slow driving the engine temp came up, and then the fans were trying to come in but cutting out before they'd spooled up, and then coming in again. Repeatedly. H'mmm. They then stayed on as you'd expect, by which time I didn't know if it was because the engine was warm or because they'd be on anyway as when the problem started. All this stopping and starting will no doubt blow the fuse at some point (I'm on a single 40A), which I'll have to look out for. Think I'll have a look and see if I can find any air-con switches looking corroded - Chim's my only car, so sadly gets taken out in all sorts of grotty conditions road-grit and salt wise...
Fingers crossed, and thanks again!
Andrew
WooHoo said:
Thanks Peter and Ade...
I agree that 4.5V is a concern, but I can't work out how a loose connection would cause a stable, low voltage (as in, I'd expect an inappropriate intermittent ground)
Nor can I. The circuit should be ignition 12V -> relay coil -> otter switch -> earth. If there's some extra way to turn the fans on I'd expect that to provide another way to short across the otter switch. If that was me I'd locate the fan relay, pull it out and measure the socket to confirm solid 12v to one side of the coil and a good connection to the otter switch on the other. From your description this isn't what you have on yours so this is where I'd start looking to see where the problem is.I agree that 4.5V is a concern, but I can't work out how a loose connection would cause a stable, low voltage (as in, I'd expect an inappropriate intermittent ground)
8V is probably enough to pull in the relay. With 4.5V on the ground line at the otter switch, you'll have about 8V at the relay.
Is your garage (and the inside of your car) dry? A drop of water between a connector on the ground line and a good ground could be enough to cause this effect.
And as others (and yourself) have said, don't rule out the A/C. In normal circumstances it will only run the fans up for a coupe of seconds at a time and only with the system switched on, but these aren't normal circumstances!
Is your garage (and the inside of your car) dry? A drop of water between a connector on the ground line and a good ground could be enough to cause this effect.
And as others (and yourself) have said, don't rule out the A/C. In normal circumstances it will only run the fans up for a coupe of seconds at a time and only with the system switched on, but these aren't normal circumstances!
Thanks to all
Car was very damp during investigation of this problem, as it was sitting in fine drizzle. Unpleasant. However, had been living in dry garage when it started, and the problem persisted after a two hour drive which I would have thought would dry the engine bay pretty well just from being thoroughly warmed. Interior is leak free to the best of my knowledge, and fuse box area is certainly dry. Might well be worth rechecking that 4.5V with it all dry though - not something I've done yet.
I'm now away from my garage and tools so investigations will be put on hold temporarily, but once I get the opportunity I think I'll start with the air-con switch - it would only need to be 20% as filthy as the front of the car got over Christmas to be a plausible cause!
Will post results as and when...
Andrew
Car was very damp during investigation of this problem, as it was sitting in fine drizzle. Unpleasant. However, had been living in dry garage when it started, and the problem persisted after a two hour drive which I would have thought would dry the engine bay pretty well just from being thoroughly warmed. Interior is leak free to the best of my knowledge, and fuse box area is certainly dry. Might well be worth rechecking that 4.5V with it all dry though - not something I've done yet.
I'm now away from my garage and tools so investigations will be put on hold temporarily, but once I get the opportunity I think I'll start with the air-con switch - it would only need to be 20% as filthy as the front of the car got over Christmas to be a plausible cause!
Will post results as and when...
Andrew
Right, have (temporarily, probably) fixed the problem via the age-old technique of finding anything which looks like it's attached to the bit you're interested in and wiggling it about a bit. The air con piping seems to be attached to a reasonably sized cylinder mounted on the off-side front of the radiator (is this the Trinary switch Ade was talking about? It's bigger than I expected, and he mentions it being on the other side...) by a clump of rust and road crap. After moving that around a bit, and to be fair moving the tubing on the near-side to check it too, the fans no longer come on when the engine is cold. Have yet to warm it up to check normal operation, but I no longer have any reason to suspect the otter switch so it should be fine...
Couldn't see or feel any obvious wires in that area, so was frankly surprised the fiddling seems to have worked. Still, gift horse an' all that. I suspect this may not be the end of it. We'll see.
Anyone know exactly what a trinary switch is, anyway? Like a binary one but with three positions?
Andrew
Couldn't see or feel any obvious wires in that area, so was frankly surprised the fiddling seems to have worked. Still, gift horse an' all that. I suspect this may not be the end of it. We'll see.
Anyone know exactly what a trinary switch is, anyway? Like a binary one but with three positions?
Andrew
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