Tool temperature can drift even when the chiller setpoint remains constant. Heat load changes after startup, flow imbalance, fouling, air pockets, control-valve behavior, ambient conditions, and changing cycle time all affect the actual mold surface.
Surface temperature should be mapped at repeatable cycle positions, while coolant inlet temperature, outlet temperature, flow, and pressure are logged. A stable inlet with a rising outlet or widening temperature spread indicates changing heat removal. One embedded sensor may not represent a large or multi-cavity tool.
The cooling circuit should be balanced and purged, flow verified, and control capacity matched to the process load. Recipe adjustments made while the tool is still reaching thermal equilibrium should not be stored as steady-state settings.