blown fuses

davidc · Post by **davidc** » Wed Mar 14, 2007 7:30 am

hello
Has anyone had experience in a tzi that, on a fairly regularly basis blowing fuse number 1. This one covers oil pressure, tacho and air con fans. It blows with the air off or on so think maybe one of the other devices... Any usual suspects here?
cheers
David

tom · Post by **tom** » Wed Mar 14, 2007 8:17 am

No, nothing springs to mind but if all the separate systems work ok then you have a wiring short. My guess is that one of the fans is drawing too much current though so I would look there first before pulling the instrument panel out.

davidc · Post by **davidc** » Wed Mar 14, 2007 11:22 am

Somthing that hasn't sunk in -
Do the dual fans need the air con on to work? Isn't the radiator located fan control thermo switch on the same circuit as the aircon. The fans run at different speeds according, to temperatue?
What should I be seeing for correct operation of the fans?
Oh and how much is too much current?
cheers

tom · Post by **tom** » Wed Mar 14, 2007 12:06 pm

Ok, we are at risk of some confusion here so let's set some ground rules. All the fans come on with the aircon so let us call them cabin fans and engine fans. I'll assume that you have the twin engine fan setup. This comes in when the engine heats up and as the first switch closes the two fans come on in series so each gets six volts and they both run slowly.
The engine gets hotter, the second switch closes and pulls in two relays that rewire the fans into parallel where they each get twelve volts and they both run fast.

If only one runs fast, a wire has dropped off and they are unlikely to run slowly at all.

If a motor had gone short, then one fan would run fast on the series setting and as the engine gets hotter, the fuse blows.

Using an ammeter, I would disconnect both fans and run them back to the battery to see what current is drawn by each one.

This pair of fans is also controlled by the aircon but as the fuse blows anyway, the fault is not likely to be here. I doubt if the fans draw more than about 8 Amperes apiece and I would be looking for a substantial difference in current draw on one fan. The wiring runs are not difficult to find if it should turn out not to be a fan but the logic is a little complicated.
To avoid boring those who don't want to understand it, PM me once you have done the tests and I'll try my best to advise from your results.

jeremy · Post by **jeremy** » Wed Mar 14, 2007 1:52 pm

Haynes (last blue and not very good edition) states that for later models fuse 1 is 10 amp and controls the engine cooling fan RELAY COIL, coolant level indicator unit, tachometer, reversing lights, coolant temperature control unit

10 amps is relatively small in terms of car fuses engine cooling fans should be powered by fuse 4 (30 amp) and the air con is on fuse 2 (25 amp)

I'd start by looking at the wiring in the vicinity of these units and see if there is any damage or sign there. I'd then see if I could disconnect or by pass the fuse 1 supply to each and see what happens. (This should only be done if you have some knowledge of the subject and alternative supplies should be fused.)

meep · Post by **meep** » Wed Mar 14, 2007 8:15 pm

jeremy wrote:Haynes (last blue and not very good edition) states that for later models fuse 1 is 10 amp and controls the engine cooling fan RELAY COIL, coolant level indicator unit, tachometer, reversing lights, coolant temperature control unit

10 amps is relatively small in terms of car fuses engine cooling fans should be powered by fuse 4 (30 amp) and the air con is on fuse 2 (25 amp)

I'd start by looking at the wiring in the vicinity of these units and see if there is any damage or sign there. I'd then see if I could disconnect or by pass the fuse 1 supply to each and see what happens. (This should only be done if you have some knowledge of the subject and alternative supplies should be fused.)

I'd add to this, and say make a start with the reversing light circuit, as of all those Jeremy's listed above, it involves the most current. All the others are very low current, low stress circuits.

davidc · Post by **davidc** » Fri Mar 16, 2007 9:46 am

Thanks for the all posts I am going to have to work a bit to bring up my test meter skills to test the current flow of the fans. Anyway at the moment my time is a bit short so I'll post when have some results. Another question could it be a one of the relays. I know one is behind number 1 fuse but where are the other(s)?
cheers
David

JohnW · Post by **JohnW** » Fri Mar 16, 2007 11:41 am

tom wrote:Ok, we are at risk of some confusion here so let's set some ground rules. PM me once you have done the tests and I'll try my best to advise from your results.

Hello Tom,

I confess to sending David here! Did you get the CD. I went again the next morning pity about the V12 focus - did you do better?

Cheers

John

tom · Post by **tom** » Fri Mar 16, 2007 1:21 pm

Nice to see you. My shots were few and yours duplicated mine. Thanks for the CD which has been copied to hard drives all around the company! Some lovely pictures of some great cars.

(For the confused, JohnW is one of the renowned Aussiefrogs. DLM and I met up with him at a rather good car show in Paris last month.)

Regarding the fan problem, You have sent David to the best place for help and I'm sure that we'll sort the problem out between us.

davidc · Post by **davidc** » Tue Apr 17, 2007 11:15 am

Well finally I can finally report back not with the fix but the answer to blown fuses. Sitting calmly in the car go through the procedure of starting car, wait for pressure annoying warning tones etc put into reverse ..pow.. change fuse..put into reverse...pow. Check the both rear light assemblies pretty clean there all other lights work ok no obvious bad earths so must be the reverse switch. Have a quick look as time was short as usual, couldn't see the wretched thing as usual. Its a tzi manual 1.9 petrol (which when I got I thought was quite flash but now getting serious turbo diesel fuel economy envy after discovering this site. Anyone want to ship a container load of good TD engines to AU) Where doth the switch hide?
cheers
David

roscoe · Post by **roscoe** » Thu Apr 19, 2007 12:49 am

David, the switch is on the top/front of the transmission just behind the clutch actuating arm - is a small brass screw-in one with a black plug on top with two wires going into it. If I recall from changing mine when it went, it only switches earth through to the reversing lamps when you put the car into reverse via a small plunger mechanism (don't have my Haynes in front of me so could be wrong on the earth/-12V bit..). You can pull the plug off the top of it, bridge the wires together and with the ignition on, that will give you a complete circuit. Sounds to me like you have a short somewhere else in the circuit though which is causing the fuse to blow - try pulling both reverse lamps out and rechecking it - sometimes they will cause a problem.

tom · Post by **tom** » Thu Apr 19, 2007 10:16 am

Check the ribbon cable that goes from the fusebox to the boot as well. Often something has worn away or pierced the insulation.

Post by **docchevron** » Thu Apr 19, 2007 12:44 pm

Yeah, I'd go with that, had the same issue a few years back, the ribbon cable had been rubbing on the plastic trim that sits on the rear valance and shorted. Replaced cable, no more blown fuses!