I have a four wire thermostat that does not work I removed it and there was 3 wires coming out the wall only two were hooked up. A red and green wire the red went to the R and the green went to W so I tried to install the new thermostat which has B,O,G,Y,W,not used,R and RC hook ups I put the red wire in the R and the green in the W same as old thermostat and no go... Any help would be appreciated

Try installing a jumper between R & Rc