Hi All
Help or ideas please.
W201 2.3 16v

With ignition in position one or two engine not running. my heater fan runs at all selected speeds.
as soon as i start the engine no matter what fan speed i select i get nothing at all no output from it what so ever.

as soon as i turn engine off and select the fan speed it works again.

is there a relay or something which could be faulty or is it likely to be the ignition switch?

any help appreciated