I had an old mercury thermostat that seemed to stop working, so I went and bought a honeywell rth221 thermostat from home depot. I installed it by following the manual but the ac heat and fan will not come on. I'm sure I connected the wires correctly because I looked at them before I disconnected the old one and the colors correspond with the letters green-g yellow-y white-w red-r. But now I am doubting I connected it correctly. The thermostat is telling me the temperature but I cant seem to get the unit to turn on. I want to try and figure out the problem myself before I have to spend money on calling a technician. Please help with any possible solutions.