[frank67ny]

I am trying to replace my old honeywell thermostat with a new Honeywell t8624d Chronotherm IV. My old thermostat is the round turning type. I just want to use my new one for a 1 zone heat in basement. There is a red and white wire coming out of the wall. The red is going to the valve and the white is for the relay. How do I connect these 2 wires to the t8624? Is it possible? Will it work? My furnace is a Burnham. Please help if possible. Thanks so much.

[tkrussell]

According to the wiring instructions, see attached link, the one heat zone needs to connect red wire to R terminal and the white wire to the W1 terminal.


http://customer.honeywell.com/Techli...0s/69-1412.pdf

[frank67ny]

I have a jumper between RC and R, Should the jumper come out. According to your wiring it still does not work. I wired the red to the R and the white wire to the C, The thermostat lcd is on, but the furnace does not turn on when I raise the temperature. Any Ideas? Thanks so much for replying

[tkrussell]

Sorry, I looked at the diagram too fast, the stat does need a third wire, the white from the transformer goes directly to the C terminal.This will provide a return for control voltage needed by the thermostat.

Surprised Labman didn't catch that. He knows his HVAC control.

[frank67ny]

What about the jumper that I have between the R and the RC, does it need to be there. Although I have the red wire from the valve (in the R terminal) and the white wire to the relay (in the C terminal), the stat is lit up but does not turn on the furnace. I treid raising the temperature on the stat. But furnace does not turn on.

[labman]

I think the white wire needs to connect to W1, or maybe W2. To power the thermostat, you need the R-RC jumper and perhaps a third wire from the C at the furnace to the C at the thermostat. If the stat goes dead when you pull the white off the C, you have to have a third wire. If you have an unfinished basement or crawl space under everything, fishing another wire in shouldn't be too bad.

[frank67ny]

I'm not much of an expert at this. Where exactly do all three wires go?

[labman]

OK, thermostat wiring 101:

Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

The old thermostat was a simple device that mechanically connected the red and white wires when it called for heat. That completed a circuit from the transformer through the valve and finally back to the transformer by internal wiring. It would have still worked even if the wires were reversed. The new one might too. I am not sure just how, but some of the digital thermostats can work with just the 2 wires. Since yours has the C terminal and the diagram shows it being wired to the transformer, surely you need it. So connect the red wire to the R and RC. Connect the white to the W1. Run a third wire, preferably blue, from the opposite terminal from the red on the transformer to the C terminal on the thermostat.

[frank67ny]

I Thank you so much for your feedback. I will do as you said.