I have a heat pump. This weekend, when I cut the heat on, the outside unit runs but the air handler will not run. It will run on cool. Can any one help?

Are you saying the fan does not run to blow the heat out of the inside unit in the heat pump mode but works in the A/C mode?

That is correct. The fan does not cut on at all in the heating mode. It does work in the AC mode. My wife said when the AC was on a couple of weeks ago, the outside unit was running but the airhandler was not running then either.

It could be the motor or the control controlling the motor. There should be a wiring diagram on the back side of the blower door. Get your meter and start checking for open electric circuits in the blower circuit area.