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phileefan5 · Jan 3, 2006, 11:13 AM

Hello, I have been trying to browse the website, trying to find out how to wire my t-stat so that it will run on auto.. I have 24v transformer, red, and white, and I connected it to the back of my t-stat, the fan turns on only when it turn the t-stat switch to heat no auto or on function. however I was reading that it would need a third wire to make it run on auto? Terminal g but I have no I dea where to hook that to on the furnace side? Do I have to buy a new really, or a new gas valve, I only have heat. No A/c any help will be appreciated thank you.

wheatnbarley24 · Jan 3, 2006, 12:05 PM

The best thing to do is buy a t- stat with the auto and on function and replace it. Sounds like all you have now is an on off switch

labman · Jan 3, 2006, 12:15 PM

Is the fan coming on now when the heat does? That is how it should work on Auto. If you want to be able to have it on without the heat, you would select ON or manual at the thermostat. For that to work, you would need a wire running from the G terminal of the thermostat, to the G terminal of the furnace. If you don't have a third wire, you would ether need to add one. Or you could install a switch at the furnace. Any simple little switch would work. Connect one side to the R terminal and the other to the G. Then the fan would come on anytime the switch is in the on position.

phileefan5 · Jan 3, 2006, 01:04 PM

Thank you for the prompt reply, yes the heat comes on now, but I just wanted to put it on auto and set the temperature on the t-stat and just be automatic, I guess my ultimate goal is to set the temp and forget it,and I want it to maintain that temp by turning on and off autmatically. Right now when I set the temp at 65 the furnace fan keeps running until its so hot I have to manually turn it off myself.. thank you in advance for the great advice. Any other things I should do.. to the furnace side?

labman · Jan 3, 2006, 04:50 PM

How long have you had that thermostat and furnace? Most thermostats work as simple on off switches. With the thermostat set to heat and auto, when the room cools, they switch power from the red wire to the white white wire. At the furnace, the power from the white wire opens the gas valve or what ever is needed to start a heat cycle. Once combustion starts the blower starts automatically by a timer or limit switch. When the room warms up, the switch in the thermostat opens, cutting power to the white wire, closing the gass valve. The blower shuts off soon after.

If you continue to get warm air after the thermostat should have shut off, try removing one wire. If the blower stops in a few minutes, the thermostat isn't working. If warm air continues for more than a few minutes, there could be a problem with the furnace. Check it and let me know. I will try to help figure it out.

phileefan5 · Jan 3, 2006, 08:27 PM

Thank you so much for trying to help me with this issue, of mine, well let me start of by saying that I replaced the old manual thermostat, with a honeywell rth110b digital manual thermostat. I guess the manual saying that I would need a third wire g to route to the fan, the manual says that if its only a two wire heating (which is what I have) then the on/auto function will not work,cause right now I set the temp and it just keeps running heat and fan. It has heat_off_cool then auto/on, I guess I have to get a new thermostat, that will have two terminals that can do auto, so that way I can put it on heat and set the temp and leave it turning off and on.? hope this fills in more info for you and again thank you

labman · Jan 3, 2006, 09:02 PM

If the furnace worked right with the old 2 wire thermostat, you should be able to use the new one. Connect the red wire to R or RH. Connect the white wire to to W or W1. Set the heat/off/cool switch to heat. Set the Auto/on switch to auto. It should now work just like the old one did. If it doesn't, it could be defective.