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  #30  
Old 20th September 2019, 04:24 PM
ainarssems ainarssems is offline
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Join Date: Aug 2010
Location: Rushden, Northants
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Quote:
Originally Posted by mannyo View Post
J126 is the part I replaced, but the replacement I got was a used one from a car of similar age.

It's quiet possible that the used one is also faulty, so I might go ahead and buy the new no OEM one from ebay.

J126 is what controls the fan speed, it has a number of inputs, and just two wires going out to the fan motor itself.

The fan is definitely running on solar power when the engine is running, you can see it spinning quiet happily by looking into the box with the pollen filter removed, ant it's speed varies based on the amount of sun.

There is 12V coming into the controller from the car side, and the voltage from the sunroof varies based on the amount sun.

It is possible of course that J255 is faulty, in that maybe the required signal is not getting to J126. I have no means of checking this as I do not know what the signal that controls the speed of the fan into the controller is meant to look like. J255 has component protection, so it's not easy to just swap a replacement in.
I think it's safe to assume that default mode for J126 if it does not receive signal is to switch to solar for example when ignition is off and climatronic is switched off. So it looks like J126 in not seeing signal from J255 either because it is itself faulty and does not sense signal, there is break or short in wiring or J255 is faulty and not sending signal. You could start checking for break or short in wiring with multimeter and if you have oscilloscope you could check if there is any signal coming out of J255 and if it is reaching J126
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