The FAST-STAT Model 3000 provides 4-wire control over 2-wire cable or 6-wire control over a 4-wire cable. With a 2-wire cable it can provide R, W, G & Y. With a 4-wire cable it can provide R,W,Y,G + any two of C,D, W2, Y2 or O/B. The most common uses are for adding air conditioning to a heating system. Can also be used for heat pumps, 2-stage heating or cooling when an existing 4-wire thermostat cable is present.