Fbh activation

[willster]

Hello, I have been activating my older pcb webasto on pin 1 via a mobile phone relay arrangement. I had cut the wire from the 5 deg switch so this wasn't functioning. Recently I had wanted to get this oem operation back and have the heater fire on its own when below 5 deg, so I routed the wire from the 5 deg switch onto pin 3. Therefore +12v goes to pin 3 when the below 5 deg. The problem is that the fbh seems to misbehave when it's run from the 5 deg switch, like the fan doesn't run enough and I've had a lot of backfiring and smoke from the air intake. I'm not sure why this is as it runs great from my phone activation on pin 1.
Would it be possible that the fan doesn't run properly on the pin 3 activation? Or is it that I've done mostly short journeys when the 5 deg switch has been activating the heater on pin 3?
I'm thinking I'd like to route the 5 deg switch to pin 1 along with my phone activation but I know I will need some sort of diode on each leg of this to stop the 12v going back to ecu or my phone relay. Can anyone help me with what sort of diode would be suitable for this purpose? Thanks, Will Read

[Arctic]

Hi Will.
Drop Devlish or Trebor (Steve/Rob) a PM i am sure that will be able to guide you or help you with what you need.
https://www.the75andztclub.co.uk/for...o=newpm&u=6974



https://the75andztclub.co.uk/forum/p...o=newpm&u=1646




You may also find what you need in this thread ?

https://www.the75andztclub.co.uk/for...d.php?t=231515

[willster]

Thanks for that I will have a look

[trebor]

Just trying to understand your issue a bit more.

Firstly you say your have an older FBH so presumably it is a 66232c model ?

If so the wire from the sensor would have been wired to pin 3 in the first place and would have fired up when engine started providing temp 5 degrees or below and would have taken its 12v from the alternator feed, so was it working ok as a supplementary heater before you cut the cable ?

To get the function back you would only have had to rejoin the wire so when you say you routed the wire from the sensor to pin 3 wasn't the wire already there albeit broken or in other words have you done anything different to the original way it was wired ?

Once a working heater gets its constant power feed it will operate in the same way whether it is fed from pin 1 or pin 3 so what you describe about operating differently is strange indeed and I would check the wiring all the way back from pin 3 to the sensor in case it is faulty, the wiring around the sensor has been known to chaffe and check your own connections too

Model 66232C is the early model Webasto and fires as a supplementary heater via the temp sensor and alternator feed sending 12v to pin 3 and as a parking heater via 12v to Pin 1

The later and most common Webasto model 98570B fires as a supplementary heater via the temp sensor and alternator feed sending 12 v to Pin 1 and as a parking heater via earth/ground to Pin 3

[Devilish]

Correct Rob.
I would just like to add that going by the model number is ok, if certain that the FBH has the original PCB. Many Thermo Top's have been subject to PCB transplant at some point in their life.

Check the PCB. The capacitors should be mounted together like this.

and not this


As trebor said, what exactly did you do when you "routed the wire to pin 3".
Did you just re connect where it was cut.

If indeed you have populated pin 1 to send a remote 12v start command, and the original ambient temp sensor command is to pin 3 then....

1/ Check the ambient temperature sensor is not faulty.
When the ambient temperature is >5°C, disconnect the wire you re connected to pin 3 (to prevent the FBH from needless start up sequence), start the engine, if 12v is present on the end of the wire going to pin 3, then you can say
"Therefore +12v goes to pin 3 when the below 5 deg".

2/ Using a inline fuse, send 12v to the end of the wire you cut coming from from pin 3, the FBH should start and run up to full load. A- regardless of ambient temperature. B- the coolant temperature is >58°C

When you re connect the cut wire, the FBH should run supplementary.

Note that when test starting and running a Thermo top, once it reaches its maximum running temperature of 71°C, it may only run up to part load when the coolant temp is <58°C.

Diodes.
Use of pin 1 for both supplementary and parking 12v start command, diodes are not needed, but if pin 3 has a circuit fault, that I have never come across on a PCB working from pin 1, or vice versa, get it looked at.

On both the Freelander Td4 and the 75, I cut the ambient temperature wire, ran 2 wires into the cabin, and installed a switch in series, so I can decide if I want the FBH to run as supplementary or not when I start the engine. They often get moved a lot on the drive without being used, taking enough out the battery, without the FBH's sticking their noses in.

Broadsword out.