2002 Tahoe HVAC controls problem ?????????????

I am having problem my hvac controls on a 2002 Tahoe LT with 265,000 miles. Here is what it doing. When you turn the speed control fan to off then the fan runs at high speed. It will just come on and off when the fan speed control is in the off position. I can not get the AC light to come on when I turn temperature to the lowest setting. Does anyone have a suggestion or solution to this issue? Thanks in advance for your time. Terry