l replaced the EATC control head two weeks ago, but my assumption that it would correct the problem was incorrect. Still doing it. If my air is blowing on high, no problem. If l put the air blowing on the lowest setting it will blow air on the low setting for a 20 sec or so and then blow high, going back to low. Any suggestions would be appreciated. Thank you.

If your A/C is set on ''AUTOthis is normal operation (the ''AUTO'' mode will vary blower speed by itself & even go in & out of ''recirc'' mode trying to do what it thinks You want it to do).Take if off ''AUTO'' setting and manually set blower speed,temp,etc. and it should stay that way untill you change it.It might self-reset to ''auto'' mode after turning off & restarting,though.

It sounds like the blower speed controller is dying, it is a small electronic devise mounted in the blower motor housing. From the outside it looks like a blower speed resister from a car without EATC. The Ford base number for this part is 16E625.