Last winter, I struggled with my ASI183MC Pro frosting over. Since where I live always has a slight breeze at a minimum, the camera would never heat up even with the cooler set to -20°C. I added the stick-on dew heater, which helped but is an ugly solution and I still couldn't target temperatures much below freezing. I thought about it for a while, but never came up with a good solution until now.
There was never a way to prevent frost because the camera is overcooled. Adding 4W of heat to the front of the casing can't compete with the at least 24W of dissipation on the back of the case due to the constant speed fan that runs whenever the Peltier cooler is on, plus whatever the wind carries away. What is needed is a way to turn the fan off independently of the Peltier, or better yet PWM fan control while maintaining a minimum sensor vs case temperature differential. For the large format cameras with the integrated dew heater, it could even be setup to work opposite the integrated heater for more extreme environments.
EDIT: The real trick to this is that a Peltier cooler just creates a temperature difference between the hot and cold sides, moving a certain amount of heat depending on how much current is applied. The actual temperature of the cold side is entirely dependent on the temperature of the hot side. Reducing fan speed to limit heat dissipation from the hot side forces the cooler to use more power to keep heat away from the cold side, keeping the case warmer. On a hot summer night, you obviously want to reject as much heat as possible to run the sensor cooler, so run the fan at full speed. On a cold winter night, the fan might not be necessary.
