Ok , a short cycle like that indicates the dash air conditioning control system needs to be checked for vacuum leaks .
Follow the vacuum hose from the pump to the reservoir ( usually a softball size black plastic unit ) disconnect the hose from the inlet and cap the hose ; If the pump no longer cycles , reconnect the hose and remove the outlet side hose and plug the fitting on the reservoir . If the pump no longer cycles you have to go to the control head in the dash and plug the supply there , if the cycling stops then you're off to individual actuators looking for a leak in the line or at an actuator it's self.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.