Odd blower motor problem

[Bobbywolf]

Ok, most of the blower issues I've seen have the blower either not working at all, or only working on high speed (resistor bad). Mine, however, is different. I have the 3 lower speeds, but no high. At first it failed intermittantly, and I'd hear the click of some hidden relay when it happened, and then it was gone altogeather. (Actually the other day it was very cold, -5 degF, and it worked for a second before 'click' and lost it). It is the middle of winter, and needless to say, it would be great to get this fixed.

Any ideas on this one?

[Selectron]

I have some service data for the 1995 north American Escort range (I'm in the UK), and it shows the heater circuit as being fed via a 30 amp circuit breaker (not a fuse). The circuit breaker will trip when its current rating is exceeded and presumably it automatically resets when the current is back within range.

It would seem likely that the click which you hear is the breaker tripping, and that would tie in with the fact that it did work on the three lower settings, but not on the highest setting - the one on which current is at maximum - I guess that must have taken it above the 30A threshold. That's a lot of current, so maybe the motor bearings are tight, or possibly, with the extreme cold weather, the bearing lubrication may have thickened and that could be adding significantly to the current which flows when the motor attempts to rotate. Oh, I'm an electronics engineer by the way and I tend to waffle on a bit when I get to talking about voltages and currents and things but I'll try to restrain myself and keep it reasonably brief.

The diagram I have shows the positive feed as being permanently connected to the motor via the 30A circuit breaker, with the ground side of the circuit being completed via the heater switch. However, it's not grounded directly except when on the HI setting - for the MED HI, MED LO and LO settings, it connects via a network of resistors, with different values being added into circuit, in series, as appropriate.

I'll post some screencaps of the wiring diagram and the switch-testing table, and they may be of some help. The former is difficult to read, but the latter is clear.

I'd say that if you're going to get it to function again, you stand the best chance of doing that whilst it's on its LO setting. Current will be at a minimum then, so it's less likely to trip the breaker, and if you can get it to run for a while in that position and allow it warm the car interior (and itself) somewhat, then you may find that it will also then run on the higher settings.

I'd say that the resistor network is blameless in this, and I also don't think that you have a wiring fault, and this is why:

If you had an intermittent open-circuit in the wiring leading back to ground, then you wouldn't hear the click of the circuit-breaker, because no current would flow, hence there would be no reason for the breaker to trip.

Neither do I think you have a short-circuit fault, because if any of the wiring from the negative pole of the motor onwards were to short to ground, well that would simply cause the motor to switch on at its HI setting, because the whole point of all the wiring and components which are in circuit beyond that point is precisely that - to complete the circuit back to ground.

When this fault puts in an appearance, if it's always accompanied by that clicking sound (and assuming that the click is indeed the breaker tripping), then I reckon that tells us that you have an internal problem with the motor, causing an excessive current draw, and as I said earlier, I reckon its bearings are tight, or its lubrication has thickened due to the cold weather. It could also be a fault in the motor windings, but I'd bet against that.

I wasn't wrong when I said I could waffle once I got started, eh. Right, I'll make some screencaps of the relevant diagrams and then upload them. First I'll go and make a cup of tea though.

[Selectron]

And here are some relevant diagrams. If the information in them does indeed refer to your vehicle then my best guess is as above - a problem with the motor itself, but I could be wrong so take a look at the diagrams and see what you make of them yourself. Also, bear in mind that I've never even seen a north American Escort, and they do differ from our models, plus mine is the diesel model so that distances me further still from your particular car.

The first diagram - the wiring diagram - is difficult to read but that's exactly the way it appears on my screen so it's just as difficult for me to read here. I've included an enlargement of a portion of it though, which is a bit easier to see. The rest of them are easily readable.

[Selectron]

And for more info on the circuit breaker, see this new thread:

http://www.automotiveforums.com/vbul...d.php?t=668642

[Bobbywolf]

Thank you for your input. Incidentially, I am an electronics technologist, so I'm no slouch when it comes to this stuff.

I've actually been over most of my blower circuit through the last couple years. Once for the blower resistor, and more recently, a lack of 12v coming in on the 30A breaker (which powers not only the blower, but also your power windows, and wipers. None of which is mentioned in the haynes manual I have, or anywhere else I could find for that matter!). Here is some background on my previous issue.

http://www.automotiveforums.com/vbul...d.php?t=641537

As you can see, the breaker is out of the equation all togeather, since there is no power feed. I ran a seperate power feed (through a 20A fuse) to the right side of the breaker socket to power all three items again. Again, the breaker is not part of the problem.

This leaves me with crappy diagrams. The ones you have posted are the same, or very similar to the ones I have in my haynes manual. They are trash, and in some cases, wrong. Don't trust them. A factory service manual is really the only place for an accurate drawing, and I'll be stopping off at my local library to see if they have it.

There is a 'mystery' relay or something of the sort that is causing my issues. Keep the ideas coming, and I'll see what I can dig up in terms of drawings.

[Selectron]

Incidentally, I am an electronics technologist...

Okay, that's good to know; I'll keep that in mind.

Well, I read your other thread and that does alter things somewhat. As I understand it, the present situation is that you have bypassed the breaker and arranged your own, fused, 12V feed, which now powers the blower motor, windows, and wipers, and those circuits have been operating normally and reliably until the onset of the problems with the heater blower.

The way I read your opening post in this thread is that you do still have the three lower speeds on the blower, but you've completely lost the highest speed, which had previously been intermittent. The way I read that yesterday I thought you'd lost all speeds but now I think you've only lost the one.

Well, if the diagram of the resistor network is accurate then there are five potential failure points which could cause the loss of just that highest speed. You're obviously perfectly capable of identifying that yourself but I'll list them anyway just so I can keep things organised in my own mind. They are:

1. One specific short section of the straight-through wiring within the resistor assembly
2. The output connector of that assembly
3. The wire running from there to the input of the switch assembly
4. The input connector of that assembly
5. One specific section of the straight-through switching within the switch assembly.



If access to the resistor assembly connectors is reasonable then you can of course check that whole path by measuring the resistance from the resistor assembly input connector to ground, with the switch on the HI setting. That should be zero ohms, and then of course you could confirm that you are indeed measuring the correct path by switching down through the different speed settings - the resistance will increase with each step, from 0 to 0.5 to 1.0 to 2.3

If access to the motor connectors is reasonable, then my next step would be to feed the motor directly with 12V. If it runs normally when fed directly then at that point I think you have no option but to start investigating the 12V feed, upstream of the motor positive pole. If I found myself in that position then I think I'd just head straight for that circuit breaker and re-investigate the original fault of the missing feed. That's easy for me to say though - it's remarkably mild here in the UK this winter but if you're having extreme cold right now then you may want to go for the quickest solution.

I keep thinking back to what you said in the original thread, about how when you fed 12V into the dark blue wire under the passsenger side dash, the blower worked on all five settings, including 'off'. That's curious, because that means that the motor already had a permanent ground - and as we know, the ground side of the circuit is switched so that doesn't make sense. Or if it didn't already have a permanent ground then the application of 12V somehow provided it with one, and that doesn't make sense either. I have this feeling that there's a there's a clue in there, but I can't see what it is. I'll keep thinking about it though.

[Bobbywolf]

You read that correctly. Feeding 12V direct to the motor gave all 5 settings. Ground is found through the resistor pack. To turn the blower off, the connection to the blower is broken. (Via the switch). When I get a chance, I'll again run 12V direct to the motor and see what happens.

I'm fairly certain it isnt a 12v feed issue, because 3 of the speeds do work, as well as my windows and wipers still. The only reason I have this makeshift bypass is because of the temperatures we are having here. I need to find someone with a garage

[Selectron]

Ah, right - I get it now. I completely misinterpreted what you meant when you said "... and connect 12v, my blower works, on all 5 settings (including off)."

I thought you meant the blower motor rotated on all settings, including the 'off' setting. You did of course mean that it functioned normally, including switching off at the 'off' setting. Glad we got that one cleared up.

Right, well in that case I think you're dealing with nothing more than either a bad contact (the straight-through contact) within the selector switch, or an open-circuit link within the resistor pack - and that would be the straight-through link, of course.

The connecting wire between the resistor pack and the switch, and the connectors at each end, would be last on my list of suspects.

The unidentified click remains a mystery, but given that the other three speed settings still work normally, I don't see what else it could be if not one of those five potential failure points.

[wintonboy]

I had exactly the same problem. Turned out it was the connector to the blower motor located just under the glove box. It had melted and shorted out internally. I temporarily fixed it with some electricians tape and then when it warmed up above zero, iIspliced in a new connector from a junker. No problems since.