I am replacing an old, circular thermostat in our church with a Totaline P374-1700. The thermostat controls only A/C, and we chose Totaline to be reset in the same way as Totaline P374-1800's which had been installed for new A/C's elswhere in the church.
The old thermostat was hooked up to 3 wires, Red, Yellow, and Green. I hooked up the same wires to the indicated terminals on the new Totaline, turned on the power, and nothing happened. The thermostat showed no sign of power or life.
I went to the previously installed P374-1800's (also for A/C only) and found that the 3 wires, and the jumpers, were identical; but the P374-1800's had an additional blue wire, connected to the "C" terminal.
Must I put in 4-wire wiring to the P374-1800, or is there a way it will work with the 3 wires already in place?