I noticed the same thing on my new 97 T-Bird. I kept hearing a noise while we were cruising slowly, so I popped the hood and saw that it cycled on and off constantly when set to panel/floor. The A/C seems to work fine otherwise.
Set it to regular A/C and see if the frequency changes. It probably will.
I noticed my 95 seemed to cycle on and off a lot when I had the hood open, even after adding a little Freon. The A/C works fine on that car too, except for occasionally having to add Freon.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles