In the Aztec and Seneca I am not aware of these limitations. It would seem at oods with the design as there is a clear gap between the screen and the heated plate so I cant imagine there would be much unequal thermal buffering in moving air. I can see nothing in the POH I have.
I also dont follow the logic, if you are going from below freezing conditions but leaving the plate on until clear of IMC and above freezing conditions the temperature differential will be far greater than if you switch it off when clear of IMC but still in below freezing conditions. Surely any shock warming would be less the lower the change in ambient temperature not the greater – am I missing something?
BTW without the internal “mist clear” on usually the screen frosts over before anything at which point regardless it seems logical to turn the shield on, and monitor the boots and props. The frost will clear from the P2 quickly once the temperature has recovered to above freezing and the shield turned off making monitoring off the external temperature redundant – albeit still a good idea. Personally I dont like the mist clear on because of the blast of warm air so I dont tend to use this anyway.
Fuji_Abound wrote:
I also dont follow the logic, if you are going from below freezing conditions but leaving the plate on until clear of IMC and above freezing conditions the temperature differential will be far greater than if you switch it off when clear of IMC but still in below freezing conditions. Surely any shock warming would be less the lower the change in ambient temperature not the greater – am I missing something?
Maybe now it’s me who’s missing some point 
, but the higher the temp. differential, the higher the risk of thermal shock, so unless I switch the plate heat off when I meet above freezing temperatures, I don’t see the risk of having that shock. But I’ll (surely ?) have some troubles if I switch it off right after I exit IMC and still in below freezing temperatures.
On my Seneca 3, the heated windshield swutch has a thermal cut out, and after 30 seconds it trips the switch off. I believe this was only on the 3.
