Originally Posted by DonA
On my wife's 2006-E320CDI and after driving about 40 minutes in humid ambient weather the AC system seemed to 'freeze up'. All controls on Auto, Temp set a 72F, car interior began to warm up. Air flow seemed low out registers, though fan speed sound was normal. Air flow continued to drop, though it did not stop. Manually raising fan speed produced little, if any, additional register flow, though fan sound increased. Turned A/C switch off for about 10-15 minutes and register air flow slowly increased to near normal. Turned manual A/C switch back on by going to full Auto and all cooling returned to normal.
Service center seemed to ignore wifes comments re. above (practiced with her and she had it down). They found a blower regulator control fault and replaced the blower regulator. Don't know the source of this but re-discussing with them got some go-round that I would have gotten massive water out registers if my scenario was valid. Don't believe that is the case as there is a demister on outlet that should catch entrained water droplets.
Finally got them to agree to recheck with another service call by letting system run on lot for 30-40 minutes. Did find out that 33F minimum is controlled by probe not refrigerant pressure level as American cars used to use to control.....Comments? Will take back in for check in a few weeks.......
I had a blower regulator failure on a W210. It started gradually and intermittently stopped blowing. Finally it got short-circuited and started blowing at full power. You however state that the blower fan sound was normal at the point it stopped blowing. Do you mean it was normal when set to max manually, the fan noise increased along with the fan speed setting? If the fan sound indicated the fan motor properly reacting to the speed setting, it does not sound like the regulator issue (even if that has been a common issue at least for W210).
If it wasn't the regulator, then it sounds like it could be the evaporator temperature sensor (no idea if they often fail, never hear of that). But this should leave an error code and in any case should be easy to read the temperature with diagnostics tools when the car is running.
I agree that there should not be any water leak problem if the evaporator got frozen, normal operation creates a lot of condensed water that but in this case it would have frozen. The fact that switching AC off momentarily helped recovering the air flow also seems to support the idea of evaporator freezing.
If the evaporator sensor is failing, the problem should be there still after the fan regulator change. Ask them to read diagnostics codes and read the sensor values when the car is running with AC on.
Finally, this control system on American cars, how can it only work on refrigerant pressure, my understanding is that all cars must have a sensor or a switch at the evaporator or behind it (a sensor or just a bi-metal temp switch). Older European systems simply controlled the compressor clutch with this temp sensor, modern compressors run continuously.