I am trying to replace a Bryant TSTAT thermostat with a Honeywell RTH23B programmable thermostat. The existing system has 5 wires, R (24v hot), G (fan), W (heat), Y (cool), and C (24v com). However, the new Honeywell system does not have a 24v common connnection. How do you wire the new thermostat to allow for the 24 return?