Weird heater issue...

[brendo22]

Hi there,

Longtime member and lurker... I have a weird problem. I had no heat in my 1.8T avant, after it was warm, checked the core hoses and the return wasn't very warm, the other very hot. So I thought, damn, heater core is plugged, etc. Proceeded to flush the heater core with CLR soaked in it for 1.5 hrs, then flushed/backflushed with hose until clear and clean. There was a fair amount of white dandruff looking flakes big and small that came out. Buttoned everything back up, am familiar with the proper bleed procedure (gravity feed coolant, wait for it to come out of bleeder on coolant pipe, then wait for it to get to the upper heater core hose. Let it get up to temp, drove it around, and proceeded to bleed from the screw, got a lot of air from there while never letting the coolant or air get back in, crack/close/pressure build up/repeat until mostly coolant) then I drove it around, came back and "burped" the upper core hose, then button up). I had the heat on hi once it was to temp.

The result was on the HI setting it was pretty damn hot when driving and didn't change much at all when at idle, so this was a great sign. THE KICKER, when I switch it to "84" which is one less on the temp spectrum, I hear the flapper mechanism make noise and then the air turns to room temp/barely warm if at all, and doesn't change much based on engine revs/acceleration etc.

So what could this be? Could it still be the heater core if it's doing great on high, and works like a champ, very hot. I'm thinking it could be something to do with the air flow adjustment in the dash? Or my control unit? It's just so weird I have really really good heat on HI at idle or driving and then nothing on the next setting down at idle or driving. Anyone run into this before? Thanks for the reading and the long post, this is driving me nuts haha!

[old guy]

From your description it sounds like your heater core is fine. Coolant is always circulating through the heater core regardless of the cabin temperature setting. If you have good heat when at idle, regardless of the setting, you know that the heater core is functioning properly.

It sounds like you have an issue with your climate control module. Clicky click®

[brendo22]

From your description it sounds like your heater core is fine. Coolant is always circulating through the heater core regardless of the cabin temperature setting. If you have good heat when at idle, regardless of the setting, you know that the heater core is functioning properly.

It sounds like you have an issue with your climate control module. Clicky click®

Hi old guy, thanks for the response. So you're saying I may need to buy a new climate control module? Are there any other things I could possibly do before going that route? I suspect it could be for sure. But could it also be one of the flappers in the dash being the culprit? Or would a calibration of the flaps help any? And last, is there any type of calibration in the climate control module?

Should I look for codes via VAG com to tell me that the climate control is bad? Can they be bad while not throwing anything?

[old guy]

The first step would be to use VCDS to check for any DTC's related to the climate control module. it sounds like your flappers are working fine. The problem is the control of the flappers. And yes you can use VCDS to reset the flapper potentiometers but I don't think that will cure your problem. The flappers are responding to a signal. You need to correct the signal.

[brendo22]

The first step would be to use VCDS to check for any DTC's related to the climate control module. it sounds like your flappers are working fine. The problem is the control of the flappers. And yes you can use VCDS to reset the flapper potentiometers but I don't think that will cure your problem. The flappers are responding to a signal. You need to correct the signal.

Ok, don't have VCDS will be able to have a buddy look at it next week possibly. Is it realistic to not throw any codes and still be bad (just want to know if I don't get anything in the CC)?

[old guy]

Ok, don't have VCDS will be able to have a buddy look at it next week possibly. Is it realistic to not throw any codes and still be bad (just want to know if I don't get anything in the CC)?

I suspect you will find some sort of DTC. If not, post back and we can research a little deeper.

[brendo22]

I suspect you will find some sort of DTC. If not, post back and we can research a little deeper.

Alright, I'll wait to get it scanned and see what I find. Thanks again, I'll report back when I can

[brendo22]

Update... my heat works now!
BUT, I didn't do anything but went out after a couple hours (warmed up then cooled down) and drove the car, and the heat was working as it should, adjusting as I adjusted the temp, heat at idle, etc. I heat cycled the engine a couple time previous and still had the issue earlier. So I think the system either just needed time and worked out that little bit more air out of the system maybe, or maybe my climate control unit needed some drive time to adjust? Honestly don't know, but if you have my symptoms, or you're system is all good and it's not working exactly how it's supposed to, maybe give it some drive time and see if things come around. Weird, but really happy with my outcome obviously!