I got it fix. removed combustion motor fan and turn by hand, make sure it it freely moving and test it then put it back. Everything working perfect. thanks to the forum.

I just moved in to a mobile home last week and I just found that my furnace is not working, 3 flashes, which mean combustion air switch failed to close. If it is really problem with that switch, then the furnace should be running when I bypassed that switch but it didn't. My thought is combustion mo...