some thoughts on the blower motor circuit. you turn the switch to an on position. very low current at the switch. maybe an amp or two. this in turns activates a relay. the relay has high current capacity, say 30 amps. activating the relay provides the blower motor with the amps required to operate it. so far we have switch, relay and blower motor as suspects if the motor itself does not operate.

now on the blower motor wiring harness recall. if per chance mercedes engineers did not properly 'size' the circuit, underestimating the current draw of the motor, then the 30 amp fuse will blow. refitting a 40 amp harness is the recall fix. and substituting a 40 for the original 30 amp fuse. you cannot substitute a 40 amp fuse for the original 30 amp without upgrading the wiring harness.

so if the blower motor does not operate we have as suspects the #44 fuse, the switch, the relay and finally the motor itself.

you have replaced the motor. (or you could have bench tested the original motor.) so for the first go around we can eliminate the motor itself.

leaves us with the fuse/wiring harness, switch and relay as suspects.

my advice. check the #44 fuse. if it is blown then replace and see what happens. if it blows again, contact the dealer to see if they will perform the recall. if not, install the upgraded wiring harness yourself.

if the fuse is ok then the relay is suspect.

kind of a trial and error type dance.

hope this helps.