WHITE RODGERS S25-51/L37-143 THERMOSTAT SUBBASE S25-51 CONVERTS A 1F72-351 INTO A HEATING AND COOLING THERMOSTAT,THAT WILL REPLACE MOST FOUR AND FIVE WIRE LOW VOLTAGE (24 VOLTS A.C.)HEATING AND COOLING THERMOSTATS PRESENTLY IN OPERATION SWITCHING:FAN:AUTO-ON SYSTEM:COOL-OFF-HEAT MADE IN USA