Fan works on defrost only

[190edude]

Searched and found nothing on this issue:

Just replaced all the actuators and the vacuum distribution module. Had a young apprentice working with me and after everthing was put back together, we took it for a ride. Had great heat, all the vents seemed to be working correctly. Cycled from max heat to max cool and turned on the AC and got ice cold air. Cycled back to max heat and it would not heat, just cold air. Fan was still working though. Let it sit for the night, came back out this morning and messed around with it and found the connector for the fan speed select was pinned out wrong. Fixed that and the fan worked fin but still no heat. After a few minutes of messing with the system the fan stopped and would not work at all UNLESS I put it on defrost and it worked like a champ. Only air was cold and not warm.
What would cause the fan to work in defrost but not on any speed selected in any other mode?