Just bought a 1999 Ranger XLT Supercab 4.0 4X4. The A/C compressor cycles every 3 or 4 seconds even when the A/C is not turned on in the cab. Is this normal or is it possibly low on Freon?
But why cycling at all when not calling for cold? Have searched the forums but couldn't find anything about cycling.

 

Welcome to the forum

Most vehicles have the AC on when Selector in cab is on any selection except OFF, in 1999 Ranger OFF or PANEL will have AC off, anything else is AC on

AC is used to DRY the air in the cab, not just for cooling, the evaporator in the cabs heater box is slightly cooled, and like a cold glass of beer on a warm day it will get condensation on the outside which is extracting moisture from the air, this helps prevent moisture in the cab's interior, which can fog up windows and cause a "musty smell"
When you breath you exhale moisture, when you get in the cab with wet cloths.............well enough said, lol
The water dripping out under firewall on passenger side is this extracted moisture

The cycling rapidly could be a sign Freon is low, try selecting AC ON and set temp to COLD see how well it cools down and if the cycling stops, if it doesn't cool as you would expect and cycling continues then yes, probably needs a re-charge

Could also be a pressure switch or another issue, but most common on a 20 year old system would be low Freon, you can get the pressure tested or rent a gauge set and test it and re-charge it yourself