Aux heater not coming apart.

Finally removed the aux heater from my car. Now, after pushing on the tabs, snapping one off, I still can't remove the cover. I see the parting line and used a sharp knife to pry it slightly open, but it is on tight. This cover must have a lip that is recessed into the bottom part.
Anyone know the trick to getting this cover off without causing an amputated finger?

Spoke to soon. I GOT IT. What holds the cover on is a small lip that has a groove in it, that is recessed down into the plastic surrounding the circuit board. The plastic surrounding the circuit board has a bead running almost completely around for the groove in the lip of the cover. Removing the cover reminds me of getting a tire off the rim, you have to get it started with one tool then insert a second tool (flat blade screw driver and a knife). I started at the narrow end opposite the big terminals. You almost have to work your way completely around before the bead and groove separate enough to release the lid with a cracking sound.
I tried to wiggle the five resistors and found none loose like I was hoping to find. I will still touch my pencil tip soldering gun to both ends of each resistor, stick it back in and try it. Shame there is not an easy way of bench testing as the four prong plug would be hard to replicate, pos. and neg connections are easy....Thanks for reading. Hopefully my description will help someone to keep from bleeding all over the place...

The resistors are the problem , even if none of them seem to be loose. As you've said, you need to reinforce the soldering at each end of them.

Yes what relumalutan said. Just put the tip of the solder iron to it for 10 seconds or so on each side and you should be good to go.

Just an update. After touching each resistor for about 5 seconds and then installing the heater still shows defective. So I bought another heater from a wrecked 2005 TDI and will swap it out tomorrow. Happy New Year to All

Update; I removed the cover of my "new" aux heater and checked continuity and whatever resistances I could note as being different from my original heater. I understand that you really should remove each resistor to test it right.
Installed in my car, this heater produced the same non-clearable unit defective error code after running a complete check and clearing faults associated with the heater swap.
Now I have something to bench test, once I figure out the polarity of the small thin 2 wire connector, unless anyone knows. A call to Ross Tech will also be made to learn more about their software and if anything can be done with clearing the 7D Auxiliary Heater Defective fault. I understand that the controller is part of the heater and this "new" heater should have had the resistors touched with the soldering gun, but I decided to try it anyway....

Opening the first heater is the most difficult. After you do your first, the rest will be easy.
The tabs will always break due to the plastic they are made of and probably the age.

I have successfully fixed several heaters. Once you fix it properly and reinstall correctly, the fault code goes away. Firstly it becomes 'intermittent' then it is possible to clear it.

Ross Tech wil be useless there, so don't waste your (and their) time on this.

A replacement heater is not a solution. It will fail within months of usage, if not weeks.

The only way to fix is to resolder the resistors and don't short anything out while you are there (there are some small capacitors nearby, etc).

And it _is_ possible to check each resistor's resistance wtih multimeter and tiny probes.

Thank you Henrick, what to expect was one of my questions to Ross Tech when a good heater was installed. I will probably turn over my spare heater to someone at work who is an instrument repair tech as I don't have steady hands for this kind of tight work. I would like to be able to bench test any heater before contorting myself to swap it out again next time..
To bench test, the small 2-wire connector I assume is 12 volts for turning on the heater. Trouble is which one is positive --- negative?? My Bently's wire diagrams are not easy to read.

No, it's CAN gateway connection.
It's not +12V, it's can-low and can-high. It needs a special digital signal tu turn it on.
You can't test it on bench.
Also, if you do it carefully and verify your work with multimeter, there's no need to bench test it.

Understood. Thank you for your help.
How can one verify with a multimeter that the solder joints on each end are good? I did place my probes on each end and got 62 ohms for the right hand three, which each also had continuity to the big negative post. The two closest to both big posts on the left checked in at 10 ohms and had continuity to the big positive post. This was on both my "new" heater and my original heater. My tester is a digital one so it should not apply too much current for checking. One thing I will purchase is a set of magnifying glasses or a monocular, which i could have used to find the door Saturday night ;>)

Maybe your iron wasn't hot enough or maybe hold it longer. Since you bought another don't be afraid to try resoldering the old one again. Worth a try.

The iron should be ~300-330 C degrees hot.
You need needle thick ends for your probes.
Be sure to check the resistance not of the resistor itself but including the resoldered joints.

When I soldered mine it took a couple attempts. I'm very inexperienced at soldering, and had to get it hotter than I thought I would.

For anyone not experienced with soldering - don't do that, you'd better buy some beer and ask your friend/co-worker/relative/etc to do that.
I recall that there are a few very small SMD capacitors around the resistors - risk of shortening them.
You need to be very preceise with this job.
Also, you need good tools to achieve best results (soldering iron with quite tiny ending).

You'd have to be a complete idiot to not be able to solder these. Granted if you've never touched a tool in your life, let someone else do it. I admit I suck at soldering but I got it working first time. You need a solder iron with a small tip but larger surface vs a sharp one.

Finally after 10 years and 200,000 miles my auxiliary heater is now working. Ended up taking it to a small local electronics shop and it was fixed in 20 min.. The repairman had a set of magnifying goggles and knew where to check for continuity from the end of the resistors to other components on the board. I will be giving my spare heater to him to repair for a backup.
In the morning, with the re-circulation closed, I feel warm air in about a quarter mile from home and in about a mile it is easily warming the ca with little assistance from the engine.

DonsJetta said:

Spoke to soon. I GOT IT. What holds the cover on is a small lip that has a groove in it, that is recessed down into the plastic surrounding the circuit board. The plastic surrounding the circuit board has a bead running almost completely around for the groove in the lip of the cover. Removing the cover reminds me of getting a tire off the rim, you have to get it started with one tool then insert a second tool (flat blade screw driver and a knife). I started at the narrow end opposite the big terminals. You almost have to work your way completely around before the bead and groove separate enough to release the lid with a cracking sound.

Click to expand...

Thanks for the description... definitely helped me get teh cover off the aux heater.

Peter

Got it done.

The 1st resistor came off the board when I put heat to it. I tried several times and couldnt get it to stick.

Google. Surface mount soldering for hints on getting it done. I ended up using some flux (plumbing is all I had ), but I got the solder to flow.

Hooked it back up in the car and ran some VCDS output tests before putting the dash back together... Looks like it worked. It was about 10C outside today, and I could see the car turning the heater on while driving with my Ross Tech.

Hoping it'll make a difference. I've had a heater code since I bought the car 4+ yrs ago and 150,000+km I've been driving without the auxiliary heater.