Air Conditioning - A/C Frozen

Hello. I have been reading many posts here, but want to get your opinions. My A/C has been freezing up after it runs for awhile. So, I called a tech to come take a look. He checked the freon, filter, coil, etc. Freon was full, coil was clean, filter was clean. The only thing he noticed was that the blower fan was set to low for cooling, so he changed it to high to see if that improved air flow. It was about 90 degrees in the house when he left. So we let the A/C run for about 6 hours, and the temp was down to about 80 degrees. When I woke up in the morning, I could hear the fan running, but there was no air coming out of the vents. It had iced over again. The temp was about 76 inside and 80 outside (therm set to 74). I know the unit is capable of cooling to 74 because it has worked most of the summer. It has iced up about 5 times this summer, but seems worse now.

What could be causing this? Everything I have read says it could be from low freon, dirty coil, dirty filter, closed vents, but none of these are the problem. The tech did say the blower fan was humming a little more than he liked, but there was good air flow until it froze over.

Any ideas?

Sounds like you have checked all. Yes the motor should have been on high for AC. Now how good did he checkout and clean the inside coil and the outside coil?????
The tech did say the blower fan was humming a little more than he liked, but there was good air flow until it froze over.
Did he amp it ????is it good?????
Also is the blower wheel clean??? dirt build up in the cup in the blades can cut the air flow down.

ED;)

He did not check the inside coil very well. He is coming back tomorrow to take a closer look. The outside unit was dirty, but has been cleaned. He did not check the amps on the motor, he just said it was humming more than it should. I will ask him to check that out as well.

Thanks for the response.