ULTRA-FUELS Model JDI-VII is a heat pump control designed for any application, which includes total electric and dual-fuel, single-stage applications. It uses only four wires, RWYG, to a single stage heat-cool thermostat. Emergency or auxillary heat is selected by clicking the fan switch to on and back to auto twice. The sequence of operation does not allow second stage heat to come on unless the homeowner decides to turn it on, and thereby takes full advantage of the heat pump and its economy. BP Porter Inc.