heater fan/blower not working with engine on
 

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

A few things:

Did this problem occur on it's own or was it like this when you bought the car.

Any recent electrical work?

I'm not familiar with the 190 heater blower control system. Is it electronic or an old style turn the knob for fan speed?

This car might have an accessory load reduction relay, maybe there is an issue there.

Does your radio / clock lose it's settings when you crank the engine? I've batteries with a shorted cell ( RE the battery is now 10 V ) droop voltage when cranking and cause all sorts of issues.

Try unplugging the aux water pump. When these go, they cause the circuit breaker in the climate control head unit to trip. Yours may be marginal, or may only be in circuit when the engine runs.

When this occurs try twisting the key counterclockwise one or two millimeters. The spring in the ignition switch, from the start to run position can become tired. The result is only one of the cir 15 contacts connect, the car runs but the blower does not.

This only happens when coming from the starting position not the off to run position.

x2 it could be time for a new key switch.

Sixto
83 300SD can be yours
98 E320s sedan and wagon

great thanks for input.

i have ordered a new battery in any case but will look at a new key switch also.

it has been sitting for a while so im trying to get bits sorted over the summer

thanks

My battery suggestion was _only_ if you have electronic HVAC controls and they are scrambling during cranking.

If you put a meter on the battery and cranking voltage drops below 9 V , they the battery could be a problem. If 9 V and above , the battery isn't an issue.