When replacing a digital thermostat with the mechanical type thermostat, you may need to replace the resistor as well.
Wiring differences between a digital and mechanical thermostat are rarely the same in both types of thermostats. These wiring differences can change the electrical characteristics of the electrical current supplied to each of these thermostats. To provide the current voltage and amperage required by the individual thermostats, a resistor is sometimes needed. You should always check your wiring diagram to know whether a resistor is required and to know what size resistor you need.
Connecting a Resistor
To connect a resistor to your thermostat, you will likely need to solder it in place.