Heater temperature varies by itself

[wiredsoftware]

Couldn't find a previous thread on this, but I'm sure there is one. My heater varies in temperature while driving, usually suddenly turning very hot even though I usually keep the dial in the middle.

 

- Often, turning the dial all the way to cold and then back up again seems to reset it

- All speed settings work (no resistor problems)

- I do not have climate control (I do have aircon, but not turned on at the moment).

- Engine coolant temperature is dead centre as it should be at all times

- Engine coolant level is fine and has been replaced ~18mths ago (problem started last 3 months, so not related to that servicing)

- Turning the temp knob to hot gives you hot air, to cold gives you cold air, in between works some of the time, but sometimes goes screwy.

 

Any ideas? Thanks.

Edited 4 February, 2017 by wiredsoftware

[wiredsoftware]

I'm beginning to suspect this... http://www.uk-polos.net/viewtopic.php?f=8&t=52145&sid=b67e60a75abc881380ac82ee7df60e5b

[vindaloo]

It's meant to find the temperature you've set, not blow air at that temp.

There's a thermometer in the heater control panel beneath a little grating.

[rum4mo]

Either way, it might be the same thing as that Polo forum topic, the air temperature will be controlled by blending the air I think, ie either let it all get passed through the heater air/water matrix or let some pass through and fix with outside air that has not passed through that heat exchanger  - now what I dont know is if all these models use the same flap motor system to achieve that blending, if so, you tend to find that the positional feedback track for the temperature flap motor, gets dirty so it needs you to whack it HOT>COLD>HOT> etc etc to clean that control track up enough to get some more useful life out of that motor.

[sepulchrave]

Yes, it's the servo motor controlled flap that's playing up.

[wiredsoftware]

Thanks all, will strip it down at some point and see if it can be repaired.

[rum4mo]

Watch out for moulded clips wanting to break off when you try to open it up!

 

I never did find the way to reliably take them apart and get the part with the positional feedback off>clean>back on without suffering damage, but there again I had gone down the road of buying a new one from VW ??!!! and leaving it in the boot for a few years before blundering on an "easy guide" to replacing that assembly - then when I had a quiet moment/bored, I got the old one apart - that was from  B5 VW Passat! (they are all roughly the same, just slightly different body mouldings to suit the different VAG applications.

 

Edit:- BTW, very hot air is tolerable in winter, what made me get my bottom in motion was very hot air in high summer, had to stop once of twice when travelling far South to central Scotland  - to let car (interior) cool down!!!

Edited 6 February, 2017 by rum4mo

[wiredsoftware]

Some info in case anyone needs to strip down the motor in future. The poster in the link above mentioned having to break off various bits to get the potentiometer out. There's a better way - first, pull out the motor element, then pull the whole plug socket upwards with the potentiometer still attached (it just slots in). Pic attached.

 

Also, the arrow on the top of the potentiometer indicates the extent of travel - if correctly installed, the potentiometer should be able to travel from the arrow at the left edge of the gap in the potentiometer's white plastic to the right of it, when you turn the big black cog on the rear of the unit from stop-to-stop.

 

Waiting on contact cleaner at the moment which will hopefully breathe some more live into it. I've confirmed that the motor works when in the car with the potentiometer removed, so it's definitely the pot that's at fault.

 

Edited 7 February, 2017 by wiredsoftware

[Breezy_Pete]

I remember getting to that stage, then struggling to get access to squirt in the contact cleaner.  Sort of bent that black disc up and squirted plenty in there, but it didn't fix it.

Depends, I guess, whether the problem is accumulation of debris, or wearing through of the resistive track material. Worth a go in case it is the former, but I suspect it's often the latter.

 

Would be bloody nice to find a source of those little pots.  Is there a part number on it anywhere, I seem to remember not finding one?

[wiredsoftware]

There's the number 162H 2479 on the side (or that H might be a K). The blue one on the Polo forum showed D04104 172, but havn't found anything on either of those numbers. Also saw the number C03523 172 on a very similar blue one, again nothing found.

 

To get access, I've cut off most of the black part (except the arrow bit). I figure there's not much to lose at this stage. The track looks intact but dull, so it might clean up alright.

Edited 7 February, 2017 by wiredsoftware

[Breezy_Pete]

Good work. This could save a lot of people paying silly money for new ones. 

Please keep taking good photos.

[wiredsoftware]

No luck finding a supplier for the potentiometer, tried various part numbers and V68/potentiometer/G92 combinations...

[Breezy_Pete]

Couldn't resist hacking my way into my Polo's original recirc. motor pot this morning, inspired by your work.

 

Under the arrow of the black cover disk is the wiper part of the pot.  Quite nice treble-pronged design to reduce wear at any one radius, I guess.  This one's a recirculation flap motor (6Q2907511A), not a heater flap motor, but everything is similar, at first glance.

As far as I can see under a microscope, only 90° of the track is used, and as per your observation, it doesn't look particularly 'carved up'. I guess the recirculation flap only moves through 90°, and the heater flap may well be the same, dunno.

 

Will wire it into a meter and explore what it's doing at the moment, and then try and clean it more, now that I have better access. 

 

Thanks again for motivating me to explore this further.

 

Edit: Actually, my memory may be wrong about what this motor module is.  When I google that ...511A part number, all the results seem to be heater flap motor?

I may be going madder.

Edit2: Found some pics of a heater box I was taking apart and the recirculation flap motor has the same part number, so maybe I'm not going madder after all.

 

 

Edited 8 February, 2017 by Wino

[Torbo]

Is it possible that something is wrong with the hand operation part on the dashboard?

 

There is also at pot meter ... that control the other pot meter?

I will put things to gather to morrow, go make a manual control?

 

 

[wiredsoftware]

Switch cleaner on the pot seems to have sorted it for now, wonder if it will last!

[YS53]

I replaced the V68 motor on our Polo last year,because of bad knees I did not want to have to do it twice LOL.

Bit the bullet and got one from VW (ouch) - about £120 istr,the job was made much less difficult by using the K.I.T.T. 'how to' thread.

Before I changed it our car sometimes used to run to Full Hot on a warm day  and Full Cold in the winter  - all completely at random  

[Torbo]

1 hour ago, wiredsoftware said:

Switch cleaner on the pot seems to have sorted it for now, wonder if it will last!

 

It is working great now! So no I have time to get som good used parts for less money.... (than new)..

Thanks K.I.T.T. fro goos adwise! 

Edited 21 March, 2017 by Torbo