Bro luweiba,
1) check refrigerant
Maybe take a pail of water.
pump water into the chiller and return back to the pail.
See if the water turns cold.
If it does not, contact JBJ service center.
2) calibration
Do you have a thermometer in the main tank?
just wondering if the sensor in the chiller can be damaged.
3) how many powerheads you have in the tank.n how many wattage are these?
Overall volume of the tank setup? inclu sump
Recalculate the HP required. maybe you missed out something.
I have seen 4 footer using 1/3 HP and it was barely enough but they were using 250 MHs.