[jamjuice]

Hi there -

I have a Mitsubishi HVAC system. I removed the old thermostat and now have 4 wires. Red, Green, White and Blue. However, the old stat was only using two; red and green. I followed the instruction from the new stats manual and other info found here and other sites but I cannot get it to work. I did get the fans to work at one point but that's all. I looked at the other end of the wiring at the unit above my bathroom but the 4 wires aren't labeled with R,G,W etc. There is a label that suggests that Blue and White go to "Transmission Out Door Unit". There are also two spare terminals.

Would really appreciate some advice/help.

Thanks!
Nick

[jamjuice]

Ps The new stat is a Honeywell RTH 6350D

[A-Cguy602]

How many wires are coming out of the wall?

The Red wire is going to be your "24v" power and green should be "fan", there should be a yellow wire and at least one more wire also.

Note: Some Honeywell t-stats do not work with certain systems; but in any-case after your thermostat is wired correctly, it has to be programmed for "heat pump", "gas", "straight cool", or "electric heat coils" depending on what you have.

[jamjuice]

Thanks for your reply !I have four wires. Red, Green, White and Blue. The old stat only use the Red and green though. Its heating and cooling with a heat pump. I programmed the new stat but noting worked. I called the Honeywell helpline and they said it's not compatible with a 2 wire system. However, I have two additional wires in the wall which are connected at the other end...