There should be a make up/fill valve somewhere in the system. I've seen both auto fill and manual fill set ups.
If you have chemically treated water or glycol systems even the auto fill valves are valved off, so you know when you dilute the system. If you have a substance in the system that needs to remain at the right concentration, you don't want leaks in the system to cause uncontrolled dilution.
If you can find the systems expansion tanks or air separator, the fill valve should be in that area.
If you dont know where are or is the make/up valve, you can conect hose water in the the lower point of system lop.
Open one valve in the higuest point of that piping lop (to vent the air from the system when the system is charged with water) then open slowly the hose valve with continuos verifycation in vent valve. After only water flow with no air bubles close valves and start the water pumps (not the chiller) Now verify again if the system is full of water in the ventilation valve for air traped or low water level.
