When your HVAC system is not working and it seems as if it is a thermostat-related problem, the issue can sometimes be resolved by checking and repairing the wiring and connections at the back of your thermostat. However, when you took your thermostat off the wall to try to fix a problem, you found that a red wire had become disconnected. Now you have two questions. Firstly, you wonder whether a thermostat has to have a connected red wire, and secondly, if so, what is the red wire for. Every thermostat needs a red wire to function because the red wire’s main function is to provide 24-hour volt AC power from the transformer to the HVAC system, including the thermostat. Without a connected red wire the HVAC system cannot work. Thus, the red wire must be connected to your thermostat as it is literally the “lifeline” of your HVAC system.…