John, Was it cycling ok this season with the old t-stat? If so, try reinstalling it and see what happens. Make sure the connections are correct. If you indeed do have a dark green wire that powers the outdoor condensing unit, it should be on Y or Y1. It may actually be blue and normally would be yel...

Flames dancing around is not good. If this happens only after the blower comes on, it could be an indication the heat exchanger is still cracked. There may be more than one crack and attempting to repair a cracked heat exchanger is very chancy.

Hmm...thought this was the heating section.

I am curious what your end result was. The outer panel on the blower compartment may feel slightly warm to the touch once the furnace has been off for a time, this is normal. Some heat will rise into the blower compartment after shut down (downflow furnaces) but it shouldn't be so hot you can't keep...

Until Robert replies to this post, does the blower run constantly or only when there is a call for heat?

One other possibility is that there is a Blend-Air system that is allowing very cold outside air into the return plenum, thus lowering the air temperature to the point of the fan switch's shut off temperature setpoint. Turn off the blend air and manually observe that the outside air damper is actual...

David, Just to add to Robert's correct response, a more powerful blower motor (hp) will not necessarily speed up the rpm's of the blower unless you tap into a higher speed. You need to know the specs (rpm) of the original motor to compare with those of a new motor and always check the temperature ri...