The diagnostic light blinks twice on Coleman Evcon #DGAHO56BDF natural gas forced air out bottom Mobile home heater. 2 blinks is supposed to be "combustion air switch stuck closed" which is called a pressure switch in the part manual. I have replaced this switch like five times through the years. Why am I having to replace this switch all the time.

You should check the intake & exhaust pipes to the heater to make sure they are not restricted in any way.
If this is the furnace I think it is, often just a tap on the switch will unstick it.