No auxilary heater (Webasto Airtop 3500)

[BoekiCaliT506]

Hello all,

My name is Bouke, I'm from The Netherlands. I have an old, but lovely, red T5 (2006) and wanted to head towards Scotland anytime soon. However, the auxilary heater doesn't work anymore and not only that, it kind of defeated me in trying to get it to work. Here's some more info:

- It's not the engine block heater;
- Tank is half full;
- It had a 25A blown glowplug fuse, which I obiviously replaced. All other fuses under left hand side seat are fine and have voltage going in and out;
- No error codes (checked the panel myself and also have had a VW specialist (not dealer) plug in his scanner;
- I removed the heater itself completely and tested glowplug + had a look inside. All looks very good.
- There is 12V going to the heater (checked the connectors under the right hand seat just before cabling goes outside through the floor);
- There is no power going to the fuel pump;
- Fuel pump is working (connected 12V to it directly);
- I had the headlining replaced earlier this year, it could have something to do with it but not sure what. Connectors and wires on backside of control panel look normal.

Please help...! As said, I kind of feel defeated by this thing at the moment which I really cant stand.

What would be the next thing to look at? The control unit that is in the heater itself?

 

[sidepod]

You say you connected 12v to the fuel pump?
It’s not a permanent supply, it needs to be modulated ie on/off which the control unit does.

The fuel pump should tick as it switches on/off.

If the heater is on the bench you can mimic the control signal to the pump simply by tapping the 12v supply on and off the batter positive. Approx 2x per second should be enough to fire up the heater.

They are very basic units these heaters.

 

[BoekiCaliT506]

Thanks for stepping in, Sidepod. I indeed tapped the fuel pump with 12V and this had the fuel pump squirting out some diesel (while everything was still mounted underneath the van). I don't have the unit on the bench anymore.

Are they really that simple? Why are there going so many wires to the unit then? Mines has 9 going to it. Let me give some info on those actually. While heater is supposed to be on, I have:

12,7V on red thick
12,0V on black
5,0V on green/white
3,4V on yellow
0V on blue, red thin, white, green, another blue

When heater is off, the 12,0V on black disappears.

 

[sidepod]

So when you switch on you have no power at the fuel pump?

You have proved the pump to be good via a direct supply. ?

The pump is fed from the control unit inside the heater so I would suspect this is faulty?

The glow plug works ok?

The fan motor runs?

Check all of the wiring for signs of breaks etc.

New control units are around £400.
Some members have reported there is dedicated VW software installed on these units. I can’t comment on that but it sounds feasible.

There is a temp sensor inside the heater unit which is essentially a switch. It may be worth checking that first as this shuts the whole thing down.

 

[BoekiCaliT506]

I assume there's no voltage at the since it only works when I manually tap it with 12V. Since it's a pulsing voltage coming from the Webasto I believe I can't measure it with standard (Fluke) multimeter, right?

Glow plug works, yes. Haven't tested the fan. Have checked wiring, seems all good.

Temp sensor is a good one, thanks! Also very glad to know the pump is fed from the control unit. I have searched high and low but was unable to find stuff like that.

Are there specific wiring diagrams or manuals for these heaters in the Cali's somewhere?

 

[sidepod]

You are correct about the pulsed signal, you can see it if you select Duty/Hz on the multimeter.

Wiring diagrams are here

Eberspacher Wiring Diagrams | Butler Technik

Eberspacher Wiring Diagrams | Download free Eberspacher wiring diagrams and schematics. Find Eberspacher technical documents for proper installation of your heater at Butler Technik

www.butlertechnik.com

 

[sidepod]

One other basic thing, in the California these heaters have a 11.5v drop out so make sure your leisure battery is fully charged.

 

[BoekiCaliT506]

Thanks again, will have a look at this next week. Leisure batteries are fully charged.

 

[McPooh-Sticks]

I have an Airtop 3500 fitted in my launch, so thought the attached workshop manual might be a help.

 

[BoekiCaliT506]

Just in case this helps someone in the future, I finally found the cause of my heater not working. Or at least I presume that this fried ECU is the cause.. Glad the whole van didn't burn down.

Hope to get a replacement soon from my local Webasto dealer.

 

[sidepod]

Ooh that’s definitely looking a bit secondhand!

 

[Gliderbee California 6.1]

Any idea how that ECU got fried? To me, that would be my greatest concern for my piece of mind ..