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Heater not running on speed 1, unless I run it on speed 2 for 5 minutes.

KeithCheetham
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KeithCheetham Proficient

KeithCheetham

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 As above, when I 1st get in my car, the heater fan will not run at 1st speed, but if I run on the 2nd speed for about 5 minutes then drop speed to 1st speed it runs OK. I have also monitored this by putting on 2nd, turning A/C on which lights the switch, then if I drop to 1st A/C light goes out within about 2 seconds. Thinking either dirty contact in switch, or fan motor brushes. Anyone else experienced this.

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Breezy_Pete Veteran

Breezy_Pete

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Not going to be a fault with the fan speed resistor?

If the speed 1 section of the resistor is blown, it'll never work on speed 1, whatever is done with switching between other speeds. R1 in this image:

 

Cabin%20fan%20speed.png

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KenONeill Grand Master

KenONeill

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If the speed 1 section of the resistor is blown, it'll never work on speed 1, whatever is done with switching between other speeds. R1 in this image:

 

Cabin%20fan%20speed.png

Not even if one of the solder joints or connectors on the R1 path is dryish or loose?

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KenONeill Grand Master

KenONeill

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Why would the AC light/switch go off when dropping to speed 1?

That is a very good question.

 

I don't know (as stated) but I do know that I can only select speed 1 on Climatronic when it's in "econ" mode, so maybe the AC demands a minimum flow through the mixer box?

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Breezy_Pete Veteran

Breezy_Pete

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Not even if one of the solder joints or connectors on the R1 path is dryish or loose?

AFAIK the usual failure mode is for that section of the resistor wire to physically burn out, but yes if what you suggest has happened, it could explain things.

 

 

@ Tech1e: If the cabin fan isn't running, the aircon won't work. Not quite sure how the 'isn't running' is sensed though, if it's just down to switch being in the off position, I agree, it's hard to explain the OP's observation.

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hutchysrs50 Mentor

hutchysrs50

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Why would the AC light/switch go off when dropping to speed 1?

 

Mine used to do that when the fan speed resistor had failed.

 

And as someone els has suggested since my post, i suspected the fan speed resistor was "failing" rather than failed with a poor joint and once used and warmed up gets a better connection. Might be a load of rubbish but i know warming circuits ups that are failed can restore them tempary.

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KeithCheetham Proficient

KeithCheetham

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 As above, when I 1st get in my car, the heater fan will not run at 1st speed, but if I run on the 2nd speed for about 5 minutes then drop speed to 1st speed it runs OK. I have also monitored this by putting on 2nd, turning A/C on which lights the switch, then if I drop to 1st A/C light goes out within about 2 seconds. Thinking either dirty contact in switch, or fan motor brushes. Anyone else experienced this.

 

 

Why would the AC light/switch go off when dropping to speed 1?

 

 Sorry, just to clarify, the light is going out when I have not done the extended time at 2nd speed to enable running on 1st speed - i.e. the fan does not continue to run when dropping back to 1st speed. I will try the resistor pack change out as had not considered dry joint.

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Breezy_Pete Veteran

Breezy_Pete

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I'm going to have a look at a spare HVAC module I have kicking around somewhere, to see whether I can work out how it 'knows' whether the fan is running or not.

On VCDS you can watch the voltage being supplied to the fan, which is presumably sampled at a point on the diagram above connected to the bit labelled L13, pin 1 of the switch connector. It would be instructive to see what VCDS saw in the two conditions you're experiencing, switch in posn 1 with fan not rotating, and switch in posn 1 with fan rotating, If it is 0V in the latter case, that would explain the aircon switching off, if that's how the module senses 'fan not running' rather than by the physical position of the switch.

Edit: Bit of a mission to disassemble, but it does indeed look like the only electrical connection between the fan switch and the rest of the circuit-board is that switch pin 1. No sign of a microswitch or other physical interlock telling the clever bits that the switch is in position 0.

Not sure how many brushes there are in the fan, but if one or more is sticking in its holder, it might not be able to start up at a low voltage input, with cold bearing grease etc. Yet the other brush(es) may be pulling down the L13 voltage cos the resistance of the motor winding will be low compared to the resistor pack.

That will make the HVAC module correctly conclude that the fan isn't running, and disable the AC.

ive had this twice .. you need a new fan resistor pack fitting

ive done it bit of a fidely job but doable just plugs in

£25 ish if i remember

Was yours working intermittently on speed 1, or never?

Edited by Wino
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KeithCheetham Proficient

KeithCheetham

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 Changed resistor pack and sorted. I was under the impression that when the pack didn't work the fan only ran on setting 4 - as they say "Every day is a school day", Thanks for the input everyone.

Edited by KeithCheetham
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TMB Mentor

TMB

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 Changed resistor pack and sorted. I was under the impression that when the pack didn't work the fan only ran on setting 4 - as they say "Every day is a school day", Thanks for the input everyone.

 

If the resistor failed altogether the fan would only run on speed 4 but it's unlikely that all the windings in the resistor would fail together.

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TMB Mentor

TMB

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Have you still got the old resistor? Wouldn't mind a look at it.

 

I chipped the ceramic stuff off my old one and found the break in the resistor wire that stopped mine working on speed 1. Was interesting to actually see it.

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Breezy_Pete Veteran

Breezy_Pete

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I'm wondering if the problem with Keith's old one might have been a dirty/corroded connection where the loom plugs onto it (the speed 1 connection specifically), since it can't have suffered a complete burn-out, if it worked intermittently? 

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TMB Mentor

TMB

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I'm wondering if the problem with Keith's old one might have been a dirty/corroded connection where the loom plugs onto it (the speed 1 connection specifically), since it can't have suffered a complete burn-out, if it worked intermittently? 

 

Sounds very possible given the failure mode.

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KeithCheetham Proficient

KeithCheetham

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Still have it - but the intermittant fault had developed since ordering replacement to the state where the run on speed 2 then drop to speed 1 no longer worked.

Edited by KeithCheetham
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