Ok guys - I'm not 100% sure what's going on here. Last year, the A4's heat stopped working. For some reason, I remember hooking the vag-com up to the heat and running the output tests and when I was going through the tests, the heat blew hot - so I figured that the climatronic must be toast.

So, I replaced the climatronic and still no real change. Then, summer came - and went. So now I'm trying to fix the heat issue before it gets really cold (it's 39 right now).

I took the two hoses off the heater core today, hooked some tubing up to each, and shot a garden hose through the core. I couldn't get a TON of pressure because the hose wouldn't seal tightly with the tubing that I had, but I could get it flowing through pretty good.

When I took the hoses off, the coolant looked pink and clean and not much different from new (coming out of the bleed side).

The water flowed through and was pretty clean. I let it go into a bucket and there were some minor, minor specks of black dirt or junk floating in the water...but it could have even been from the bucket. The water seemed to come out clear. At one point I blew through the tubing with my mouth and with some pressure I could get the water to flow through just with mouth pressure.

I then took an air compressor, filled the tubes with water and blew air through the hoses to force the water out at a higher rate of speed. I did this a few times. I then reversed the hoses and did the same garden hose and then garden hose/air pressure trick going the other direction.

The water came out clean, seems to flow, etc.

I reconnected everything, filled the resevoir, and started bleeding. It seemed like I was getting no-where. I tried revving the engine, and then letting off - at which point some air bubbles would come out...I did this probably 50 times. I then pulled the return hose off the resevoir, put a bolt in it so it was sealed, and blew some compressed air into the resevoir inlet - which caused coolant to come shooting out of the bleeder hole on the heater core and out, over the front off the car (I had it at 60 PSI). I put the hose back on, revved and bleed by hand a few times and buttoned it all up.

Even at this point, I feel some heat coming out - but I feel like it should be much hotter. The hose going into the core was so hot it almost hurt to touch - the hose coming out was warm but not hot. The air coming out of the vents is luke warm at idle it seems and mid-warm when the engine is under load.

The upper radiator hose and all hoses other than the heater core outlet hose are VERY hot. If I squeeze the upper radiator hose, I can feel the outlet hose bulge as if fluid is being pushed through. I can almost see the outlet hose move when I do this also.

I'm not sure what else this could be? I know the blend doors are all working because they work when I run the output tests in the vag-com. All the hoses are hot except the outlet, which to me suggests low flow (since it's warm) - but I don't think the heater core is blocked since flushing it went so well and it looked so clean, etc???

Any ideas on how I can get my heat burning hot again? Thanks guys!

 

I bleed the system with the engine cold. I open the bleeder and use compressed air at the coolant tank to force out air pockets. It takes only a few seconds and is very effective.

 

I essentially did that when the engine was hot - and it seemed to have worked better than the waiting around for a 1.5 million air bubbles to come out - but it's still not burning hot.

Maybe I just need to drive it around a little? It's at least warm - which is better than it was before - it was blowing cold air all the time.

I guess I'm worried a little the heater core is clogged, even though it seemed to flow. My garden hose has a fairly low flow rate, but when I filled the tubes and blew air through...the water came out of the other hose so fast the hose whipped around for a few seconds with strong force....I had to have my dad hold it so that it wouldn't go everywhere.

I also have a similar problem on my A6 - but the resevoir is cracked and leaking so I have a new one on order...meaning it may not be fixable until the crack is fixed...

 

You need to flush and back flush the heater core AND the rest of the system. I had this same issue and once I flushed the entire system everythin worked.. also buy new g12 from dealer, got mine from audi for $25/gallon.. just pick up flush kit from any parts store (auto zone checkers etc) then make sure u get all air out.. unbolt reservoir and raise it up in the air higher than the core and pull heater core hose back until hole is exposed and then add your coolant.. you will notice water fountain coming out of the hole, do this until the water is gone and your pink coolant is coming out instead. (You will need to continue adding coolant, I was surprised how long it took to get coolant coming out instead of water) then top off the system and put cap back on... start the car rev it up to about 2200rpm and hold it for about 3 minutes and then let it sit at idle until lower radiator hose is hot.. open reservoir and top off if necessary (coolant will be hot so use a towel to open reservoir)

Goodluck

 

Audimaniac - sorry, I thought I replied to this a couple days ago, but I guess it didn't take. I was posting, doing about 3 different things and I probably forgot to actually post.

Thanks for this input - I will try this over the weekend. The heat in the car works just a little at this point - but not great...although my gf says it seems to be getting better and she actually had to turn it down yesterday.....it's still not boiling hot though and I think it should be...especially when the single digit weather hits.

 

its the heater core. If you cut one open and saw how it was designed, you would know why flushing them does very little. It will seem like its flowing fine and comes out clean, but take it out, cut it open, its packed full of debris and sludge sort of stuff. Theres just not enough hot coolant flowing inside to transfer heat. A4s and Passats suffer from this quite abit.