How carb heat affects manifold pressure
Hello,
I'm a little bit confused of how applying carburetor heat affects manifold pressure in constant speed propeller aircraft (this particular matter concers C182 with O 470 engine).
Assume cruising with 2200 rpm, manifold stays within green range, lets say 19 inches.
Normally it should acts like this: aplying carb heat shouldnt change MP value (keeping constant pressure) either rpms. I wonder why sometimes after closing the heat, MP is rising above previous value even if no icing conditions occur (carb temp gauge shows 10 degrees or more, no moisture etc)?
Moreover why sometimes when applying carb heat, MP rises immediately, even 2, 3 inches? It should be correct for fixed pitch propeller but why is this happening while in governor range?