Aux fan does come on when A/C is on... However, there is another trigger for
aux fan... which is secondary circuit that in the event of overheating at
105 degree celcius.
Majority of the time when aux fan doesn't work when a/c is on...wordy I
know... is the thermoswitch... or the fuse if it doesn't come on at all...
Last resort is dead fan.
My C-class blower fan (main fan or Aux) often doesn't come on, suspect it's
not the switch because the functions of the switch do work when the fan
actually runs. Could mine be the same problem? if so, where is the
thermoswitch and how do I test it?
Yes, it comes on with the A/C on. It is triggered by the pressure of the high
side of the A/C.
On top of the receiver-drier is the pressure switch. If it is green, it turns
the fan on at 325 psi.
If it is red, it turns the fan on at 275 psi.
Back in the early 90's, there was a big ACC update for 190E's [in the USA]. Part
of it was putting
on side shields so all the air would go thru the condenser, instead of around
it; changing both
drier switches; and adding wiring and a black top relay so the magnetic clutch
fan on the water pump
would lock whenever the aux fan was engaged with the A/C. This lowered head
pressure and vastly
improved the cooling capacity and kept the manifold hoses from blowing up.
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