when to replace fan belts

bass n bob wrote:
I have the Ford F53 Chassis with 30,000 miles. At what point should I think about getting the fan belt replaced? I can find no reference to it in the owner's manual. THX

Age, heat and dry cracking, upon inspection, might dictate more. If it's a modern single serpentine belt with a belt tensioner, then it could be good for 100K miles easily without the effects of aging.
Thing is, if you're not carrying a spare that you know will work, you should install a new one and keep the original on board for an emergency. Also learn to change it out in your driveway and carry along what you need, since it's a lot easier learning this at home, than it is, in the middle of Death Valley.