RedDragoN750

I am going to be replacing the heater core in my 96 A6 Avant. First, how does one get the radio code (I assume the stock radio ****s itself when disconnected)? Second, what does one do with said radio code. austinado16, was your (very detailed) how-to on your 95 A6? Any other tips? Lastly, I'm hearing about a valve that may also fail, making it seem like the core is plugged, anyone know anything about this?

DaveInSaltLake

with the owners manual and all the other same-sized brochures that came with the car. Some dealers write the code on the factory options label found under the carpet in the trunk.

The 4-digit code is also sometimes written on the radio itself if someone has replaced it or had it out for some reason.

Worst case scenario, the dealer can provide it based on the radio's serial number. Some charge up to $75 for that service....some less.

DaveInSaltLake

going through all the work to replace it.

What are your symptoms and what have you done to troubleshoot them?

Reference the FAQ for the procedure to check for trouble codes in the climate control unit and system.

austinado16

This is not a job you want to do, especially in the winter when the plastic parts will be cold and so will the sealant that holds the heater box to the firewall. The chance of breaking stuff is just too great.

Heater cores fail in 2 ways.
1) They leak and you'll get steamed up windows with the heat on, and usually a maple syrup smell.

2) They become plugged so no coolant, or very little coolant is flowing through them, so even on full heat, you don't have much warm air coming out.

Understand that on our cars, the heater cores are full of circulating hot water water at all times. In order to transfer that heat into the car, a "blend" flap is actuated and "opened" just a certain amount depending on the tempurature setting you've chosen. If this flap doesn't open at all, or doesn't fully open, then you don't get enough airflow through the heater core to overcome the cold air entering from around the heater core.

<img src="http://pictureposter.audiworld.com/57225/heater_box_heater_flap_diagram.jpg">
In this photo you see the passenger side of the heater core. All air enters the heater core through that big hole on the lower right. Where that air goes is controlled by the blend flap position. (noted in red and blue)

You can watch the linkage for the blend flap function either by activating the climate control with the engine running....and changing the temputure settings. Or in VAG-Com by looking at the Climate Control computer and selecting "Output Diagnostic Test Mode" and running through each item that is actuated in this mode (when you get to the blend flap it will swing that flap back and forth repeatedly).

The heater control valve you speak of is on the driver's side of the heater box. Lift the hood, remove the big black plastic tray/panel that sits there in front of the windshield, and then you'll see the heater valve in-line in the upper heater hose.

The system receives vacuum from the engine via a 3mm cloth braided vacuum line that comes out of the left (driver's side) side of the throttle body.....goes through the firewall and connects to a black and yellow check valve. Then it "T's" off to the heater valve and 2 other valves.

Make sure you are getting vacuum, that your 3mm cloth braided lines are in perfect condition, and that the system holds a vacuum. I recently found that I had a leak in the black spagetti lines that run across the top of the heater box(in the photo above). Repairing them has cured a rough idle and a problem where the heat and the dash vents would come "on" while driving up a steep hill.

So do you diagnostics before you condemn something and start throwing parts at it. You'll be glad you did!

RedDragoN750

symptoms are: Very weak heat, not a lot of air blowing, upper heater hose (by firewall) cool and lower hose very warm. Also some air blowing over by where the pollen filter should be.

austinado16

1) Clean the debris from the air intake locate where the pollen filter should be. There is a door back against the firewall that opens wide (or should) when the system is "on." There is another door inside the car and up behind the glove box at the firewall. This inside door is the recirculation flap. Open it and clean out the debris. Compressed air is your friend here, as is a long soft paint brush...or similar.

2) Once this is done (or you've confirmed that it's already clean) Check for vacuum getting to that heater valve on the driver's side of the heater box....engine running. Check for vacuum leaks using a Mityvac.

3) Once you've confirmed that you've got vacuum and a working valve, it would be worth it to open that bleeder screw there in the hose just after the heater valve, rev the engine and hold it at 2,000rpm and make sure you just have straight coolant coming out past the bleeder screw. This screw is plastic so don't break it!

4) Next step is to check the function of the blend flap. See my previous post.

5) Next would be to disconnect the heater hoses from the heater core, slip on some of your own hose, press your pistol grip garden hose nozzle against one of your hoses and back flush the heater core. Actually....flush it both directions.

6) Following flushing, reattach your car's hoses, loosen that bleeder screw, top off the coolant tank, bleed the coolant system, and then check the heater's output.

I definately wouldn't replace that heater core until I'd done all of this.

RedDragoN750

Thanks for all the advice. The big concern is the amount of air I feel blowing around that pollen filter. I've cleaned a subway bag and two napkins from inside this area, but when the heater is on there is a lot of air escaping here. Also in removing the hoses from the core to flush it, wouldn't it be just as easy to take the whole thing out? Or are you talking about cutting existing hose then coupling it back together after?

austinado16

Heater core removeal and reinstall is typically a full 8hrs your first time around, if not more.....depending on your skill level. It's not a job you do if you don't have to. It'd be like removing the front subframe because you have an alignment problem.

Pretty common for the evaporator to suck up loose stuff out of the glove box or off the floor. The VW Jetta/Golfs did it back in the 80's.

I'm not sure I understand where all the air is going or coming from. The system takes it's air in, either from the open door at the back side of the evaporator box, or from the open door inside the car behind the glove box.....one or the other, not both. Many times the spring that holds the inside door closed tightly will be broken, or the vacuum hose that operates the vacuum diaphram to close and open these doors goes bad...resulting in the doors not opening or closing correctly.

You really need to spend more time checking the functions of the system.

For flushing, all you need to do is pop the hose off at the heater valve, and the one off at the lower fitting on the heater core. Then slip on your own hose and back flush with a garden hose.

RedDragoN750

Wise you are sage one, hmmmm (yoda voice, lol)! Sounds like you're asking about the leaking air by the pollen filter... in which case if you were to take off the snap-on *rain gaurd* by the wipers, and stick yor hand down, wrist deep, in the area by the fender, you would feel a fair amount of air blowing on you.

P.S. Thank all of you soooooo much for making a noob feel really welcome with ALL your tips and tricks for this, that and the other that I've been asking about (poor VW boy sheds a small tear) *sniff*.

austinado16

Just trying to steer you to the path of least resistance.