2010 W212 AC blower makes lots of noise, but barely any air comes out
 

About 20 minutes into a 3.5 hour drive in the Alabama summer Monday, my AC stopped working. Changing the fan speed does make the blower get louder, but there's no noticeable difference in air output from the vents. Changing the "mode" from the upper vents to the lower vents doesn't seem to do anything, so I'm guessing some sort of control solenoid or some junk has gone out. I read a few threads about this for the older cars but didn't see any how to guides or parts lists or anything. This problem sound familiar to anyone? Any articles/threads on how to fix it?

2010 E350 4matic, 77k miles

If you let the car sit for several hours, does the problem correct itself? Coil freezing up maybe? Cabin filter?

^ Good call.

Alabama. How humid was it?

When I get home after work I'll crank it up and see if the AC is working now that it's been sitting. I just replaced the cabin filter about 15k miles ago so I don't think that'll be the problem, but I plan to check it.

Humidity...all of it. I checked weather history and it was between 60 and 85% during the time I was driving.

Ice clogging evaporator coils melts pretty fast once the compressor is shut off, so during a long drive it's pretty easy to click off the AC for several minutes once in awhile. There can be a huge release of water vapor each time you do it (enough to fog the windows), so you might have to open a window for a bit to vent it to the outside. Hopefully it's not raining at the time.

Sorry for the delay in replying. So I went out and cranked the car up, and air is blowing just fine, all blower speeds result in varying amounts of air, with the highest being strong enough to ruffle my hair about considerably. Monday I had to put my hand directly in front of the vent to feel any air.

So do you think this was caused by the evaporator freezing up? My truck (86.5 Nissan D21) has a sensor in the evaporator that detects ice and shuts the compressor off for a bit to let it thaw out. I'm assuming the W212 has something similar that is perhaps malfunctioning?

No ideas? I know you can turn the AC on and off to fix it, but I'd rather address the actual problem.

It certainly sounds like the evaporator froze up. The system may be low on charge, the cabin filters may be dirty, or some sort of sensor may be bad. There should be a cutout of some sort to shut the compressor off if the evaporator gets too cold.

I'm not much help diagnosing further, my knowledge of these cars stops with the W126/124. I vaguely recall someone in the diesel forum a year or two ago posting about a W211 having an updated firmware or sensor to deal with high humidity levels and preventing frosting of the coil. I'd imagine that the 211 and 212 share some commonality there.

There may be a way to enter some sort of diagnostic mode and see the temperature displays from the various sensors. If so, check the evaporator temperature and see if it's a reasonable value.