Evap fin spacing and freezeup

[desA]

I was thinking along those lines, coil depth, air velocity etc. Obviously the moisture would freeze quickest at the coldest point but whether the majority would reach that point is the question in my mind as it would depend on how quickly the moisture would condense upon impact with the coil and therefore where in the coil it would deposit.

Based on the TL diagrams above - where would the first ice begin forming?

I do suspect, though, that there will be different weather conditions to consider:
1. Cold air, with moisture;
2. Snow blown into evap inlet;
3. Snow falling onto evap discharge.

The evap/fan coupling & direction of air-flow through the heat-pump will play a part here.