When driving on a cold rainy day, I turned on defrost heat to clear my windscreen. No heat came out. AC, fans and zone select worked fine, but no heat. So I had to stop repeatedly on a narrow road to wipe windshield. After reviewing user forums, some pointed to a known problem with these Sprinter vans. Apparently the actuator servo motor that controls the heater flap can get stuck at limit positions and fail. This explains why my heater is stuck on cold. Also mentioned in forum, there is also a manufacturer software update that prevents this issue by keeping the actuator servo motor from moving to the very last position (cold or hot). This simple preventive fix was never offered to us during our warranty period. Some forum users went further with a modification to servo motor shaft — apparently this fixed the undesirable flexing on heater flap. Now that the servo motor has failed and I no longer have any heat, I do recognize that there were warning signs. I now recall there were occasional instances where my temperature select did not have any effect until I drove the temperature all the way up or down. I believe this was the servo motor getting stuck briefly but it became unstuck before it completely failed. I feel this can be a grave safety issue because of individual circumstance. Most times it may be an annoyance. But in certain conditions (as I experienced) it will be a significant impediment to driver visibility. It also exposed me to roadside risk when I stopped to wipe inside of windshield.