You will likely get several answers here soon. If it begins blowing cold and then turns warm, it generally means that hot water for the heater if flowing through the unit. The AC can't overcome the heat and warm air blows. There is a valve that commonly goes bad that needs to be replaced. You can also use a manual valve, but must remember to turn it back on in the cool weather to get heat.
I'm sure there will be others along soon with a more descriptive answer for you.
Tom and Barb
'07 Winnebago Voyage 35L
Workhorse W22 chassis FMCA 219315