A4 B6 heat issue..... yes another one!

[pimp'n]

So I've read and watched a number of videos on this subject over the years and I have tried a number of fixes but still getting nowhere with this. I drive the car in the summer so not a HUGE issue but I would still like it working etc etc. So I've flushed the heat exchanger (clean and flows) checked the coolant, I have pressure coming out of the exchanger, coolant in the reservoir, blower works. Car get's up to 90 degrees and thermo cluster etc works. I pulled the glove box and the flap controlling the air re-cycle does not operate properly however this appears to be a separate issue as there is no heat regardless of the positioning of the flap (open vs closed). There is air coming from all vents when activated (def when set to def, vent when set to vent, floor when set to floor etc). air con works fine as well. I'm wondering if there's another vent I can't see that is bypassing the heat exchanger or something? There is an engine code but that's new and when I pulled it. it's a 4020 code which relates to the cat convert from what I read so again not related (regardless this is an old problem and a new code.....). Appreciate the input!

[Cybersombosis]

When you touch the upper and lower heated core hoses when the car is up to temp, are both hot? When you flushed the core, did you flush in both directions 5-10 times? When I say flush, what did you use to flush it? Air? Water? What source of water? A garden hose? Just distilled water and no pressure? Being descriptive will help us help you.

[pimp'n]

flushed the core BOTH ways several times....... don't recall exactly how many but several and the water coming out was clear. I used a garden hose.... admittedly it wasn't "high" pressure but the flow rate was good. I hooked some black tubing to teach end of the exchanger and flushed into a bucket first from the exit then the inlet rinse repeat. Heat wise, both hoses are "warm" to the touch. I would say they neither were "hot" but they were fairly uniform, the exit hose being slightly cooler which I thought was a good sign until I got into the car and there was no hot air coming out of the dash vents.

[Cybersombosis]

How long ago did you do the flush and did you ever get heat after the flush?

Have you scanned for codes on the HVAC module? If there is a flapper motor broken, it will tell you.

[pimp'n]

flush was a year or two back but no there was no heat after. If I thought it would do anything I'd flush it again..... simple job but as I say it did nothing last time..... like ZERO. .... and the fluid is clear pink flowing out of it now under pressure. My VAGCOM is down so used a regular ODBII reader to get the 4020 code. I have not been able to read the non-CEL codes with that one obviously.

[Mike Tries]

If you've got a mineral coating on the inner surface of the heater core, it could be acting as an insulator, preventing the heat from getting into the unit itself, but not necessarily blocking the flow of water. I also did a garden hose flush, but I also filled the thing with CLR for a couple of hours (or overnight maybe). That was last year, I still have great heat. You may want to consider not using CLR, though... I think people here say Mercedes-Benz has a good cleaning chemical?

[pimp'n]

I may actually have some oif that around. I'll give it a shot.... at very least rules out an issue. Cheers.

[SideMirror]

https://irontite.com/p/8189-thoro-fl...RoCqNwQAvD_BwE

I used this to clean the stop leak from a coolant system. Works well and is compatible with aluminum. Some over the counter cleaning chemicals will react negatively to aluminum.

Sent from my Pixel 7 using Audizine Forum mobile app

[Mike Tries]

Yeah, I suggest not using CLR. It worked for me, but I don't know if it might have caused some damage in there. Apparently, it reacts with aluminum--maybe it pits it, or messes with the oxide layer? It might not matter for the inside of a heater core (as opposed to some finished-looking bit of trim in your house somewhere). I'm not sure if you may have been referring to having some CLR around or the Mercedes-Benz cleaner, but CLR may do harm if you're not careful.

[pimp'n]

k so I was ref to having CLR around..... sounds like maybe a splash of vinegar or some such may be in order instead? I spent some more time messing around with the servos yesterday and turns out the blender flap motor is actually ok.... so again I'm at a loss unless there's some stubborn air gap some where. I have bled it from the hard pipe on top of the motor and again from the heat exchanger itself and no difference. I will give the back flush a try AGAIN today and see if it helps but I checked both pipes at temp again yesterday and both were nicely heated to the touch eventually. The rad top pipe was considerably hotter but there was for sure heat in both the in and out pipes of the exchanger.

[pimp'n]

https://irontite.com/p/8189-thoro-fl...RoCqNwQAvD_BwE

I used this to clean the stop leak from a coolant system. Works well and is compatible with aluminum. Some over the counter cleaning chemicals will react negatively to aluminum.

Sent from my Pixel 7 using Audizine Forum mobile app

Cheers. I will have a look at this! Thanx for the input!