Hi, I'm new to these forums. I have a pretty good idea how things work but I'm a bit puzzled by a couple of things re thermostat to furnace wiring. I just bought a new Honeywell 9580 Wifi thermostat. I have a Carrier 2 Stage furnace and I believe a single stage AC. There are no other systems or controls except a furnace mounted humidifer that has it's own controls. I'm not concerned about the AC at this point but it's relevant to the wiring of course. Anyway my old thermostat had 5 connections wired - Y, G, RC, R, and W/OB. I'm not sure why it has separate RC/RH connections because I thought those were usually just connected with a jumper. Both the R and RC wires are connected to R on the terminal block on the furnace. I pulled a new 2 conductor wire and connected C to the 24V Com on the furnace as this thermostat requires a C wire. The menu on the new thermostat asks if I want to have 1 stage or 2 stage heat. Since I only have the one wire connected W, I just indicated one stage.

Question 1: If I want to use it as 2 stage, I assume I have to connect my remaining conductor wire to W2 at the furnace and thermostat. ? Do I have to change any DIP switches on the Furnace control board?

Question 2 - Twice in 2 days the Thermostat has gone dark - seemed to lose power then start up again. Honeywell Support (more on them in a minute) told me I should connect the C wire to the "cooling transformer" for the AC not the furnace 24V common - this makes no sense and I wouldn't even know where "cooling transformer" is. There is absolutely NO mention of this requirement ANYWHERE in Honeywell's instructions or videos so I'm really skeptical.

Question 3 - The house seems to overheat during the transition period in the programmed schedule - I have it set to go to 22 C in the morning, 20C during the rest of the day and 18C at night. I understand this thermostat is supposed to have a learning function and is supposed to start ramping up the temperature earlier so that by 7:30 am it hits the 22C mark. During this period, the "Set Point stays at 18C which makes sense but the furnace heats up to 24C based on comparison with 2 other thermometers only shows a room temp 20.5 c or so., not 24. (The rest of the time the thermostat agrees with my thermometers.). During the day and at night, it seems to agree with the programmed settings and run correectly, It just seems to overheat the house during the transition and also show the wrong room temp at that time.

Any help would be appreciated!

Re Honeywell Support: 20 minutes on hold then the usual off shore service rep following an onscreen check list. Wanted me to reset to factory default which I did, then when it was running continuously in the morning, pull it off the wall and put it back to see if it made any difference in the temperature - So basically wanted me to call back in the morning. When I questioned the logic in doing this, he got angry and told me I had to co-operate!

This post was edited by hockeymagnet on Thu, Jan 16, 14 at 12:30