I have a trane a/c unit that start blowing cold air than after some time it blows warm.if I turn the unit off than back on it blows cold.can any one help?

Is the outside unit still running when the warm air starts. You need to get up close and see if the compressor and fan are still running outside. There are many things that could cause this. May be time to call in a pro.

I have no idea why starts is tagged.