Stainless Steel Fenwal Thermostat used in all larger style units with stainless steel troughs.
The adjustable range of the Fenwal Thermostat is from 0o F (-18o C) to 100o F (38o C). The thermostat is not preset at factory. To adjust the thermostat to the desired temperature, first fill the trough to proper water level then check the water temperature with a thermometer. The next morning, check the water temperature again. If the water is warmer than desired, turn the thermostat down (clockwise). If there is ice forming on the surface of the water, turn the thermostat up (counter clockwise). Only slight adjustments should be made to the thermostat at any time. A 1/16 turn on the thermostat will change the water temperature 7o F (4o C). The most economical temperature for the trough is 44o F (7o C).
Fenwal Thermostat - Stainless Steel 16534 - Ritchie Industries, Inc (ritchiefount.com)