“I am replacing a Honeywell MPLS.MN with RTH958WF. I was told I need a C wire. The exist thermostat has Yellow, White, Red, and Green wires connected to Y, W, R, and G terminals. There is a blue wire but it's not connect to anything. Use that as C?”
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I've got a couple of units and both of my C wires are blue. That's pretty common, I think. Also, from what I understand, some installers don't hook up the C wire if it's not necessary. That would make me think that's a C wire, but I'm a DIY'er.
Sorry, there was a problem. Please try again later.The blue wire needs to be connected to the C connection on your furnace control board. If so, it would be the C connection you need.
Sorry, there was a problem. Please try again later.Yes, C is your blue wire. If ur not sure try it anyway. It low wattage and won't do any harm (at least that's what my geek squad guys told me). You might also want to consider Google Nest 3rd generation thermostat. It works with most configuration. It's a little more money, but in the long run will be better( in my opinion). I tried this thermostat but it did not work.
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