2002 Tahoe heater/AC fan switch

I have a 2002 Tahoe LS 4WD. It has 33,000 miles on it. The heater/AC control switch does not activate the fan in the #1 and #2 setting. It only starts blowing on the #3, 4, 5 settings. When you place the switch to the #1 or #2 setting, the AC or fresh air light comes on but the fan doesn't blow. I replaced the switch/control unit but its the same. I installed my original switch unit in another Tahoe to test it and it worked perfectly. I'm stumped.