I have a coleman evcon furance in my doublewide, model:96-8w4w-2p serial:m0723070234, when its cold out side it blows cold air, if the temp out side is 50 or higher it blows warm air. What could be causing this?

Is your double-wide placed on a foundation or is there skirting around it?

Sounds like maybe the return might be pulling air from outside instead of recirclating the air from inside your house, check ductwork to see that its connected correctly.

It is on a brick foundation.

Does the trailer still have an insulated "belly", or is the ductwork exposed to outside temps? Also, does your unit have a fresh air intake with damper?

The duct work is covered,outside temperature can't get to it.

Along with mygirlsdad77's questions, is the brick foundation a basement or crawl space?

How cold is the air? Does it seem to be semi warm or flat cold?

It is a crawl space and it is semi warm.

What about the fresh air intake with damper? Does it have one?

Don't know about fresh air intake it maybe under the house I don't know.

This is a must to find out... you will either have to go under there or hire a qualified technician to do so. In a circumstance as yours, it should have been an automatic damper and not manuel but that doesn't mean that is what happened. Let us know

Your setup may be different, but the Coleman Evcon trailer units I have dealt with have a fresh air (makup air) just inside the top (blower) compartment. There would be a control box with on, off, and an alarm light. This is usually ducted right into the attic (if any) or right to a motorized roof vent which kicks on when the damper opens, sometimes controlled by outside air temps. Some areas require these by code for trailer homes, ours does not, so we usually don't install them on new furnaces for reasons just like what you are experiencing.. We can get months of well below freezing temps in my area, and find that the fresh air intakes kind of defeat the purpose of heating. Not real efficient bringing in cold air to heat in my opinion. Don't get me wrong, there is definatley a place for fresh air (commercial buildings etc), but If you have one in your trailer, I would plug off the fresh air intake, disconnect the wiring, or otherwise kill power to it and see if your problem is cured.