1997 Taurus A/C

My 1997 Ford Taurus has about 137,000 miles on it. The other day, I cranked it up as usual and a mile or so down the road, turned on the a/c to a midrange cool temp. However, cool air did not come out, only warm. That's the way it was for the rest of the (very hot) day. It sounds like an a/c fan or something is cutting on and off up in the motor area. Can someone give me a heads up what the problem might be? Thanks.