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thunderhead 06-19-2009 02:11 PM

Changed thermostat, not working
I had a new furnace/ac unit installed about three years ago. Always hated the t-stat they supplied with it, was dimly lit and hard to read. Finally had enough of it today and changed it to my old one.
I don't know what brand the one they supplied is, all I can find on it is VT2005. The one I replaced it with is a Honeywell MagicStat/3355. The Vt was a four wire, red, white, yellow, green. I hooked the Honeywell up the same way. Whether it is on heat or air the fan comes on after about ten seconds. The furnace never ignites and the blower keeps running. The air does work, shuts on and off, but the blower keeps running on that also. I do not have it set on constant fan. When the fan was running I switched the switch to system off and it kept running. I then removed all four wires and the fan kept going. I had to go cut the power to the furnace to shut it off. Any ideas? I can not put the VT back on because it got broken during removal. TIA

Brik 06-19-2009 02:17 PM

It could be one of three things.
1) You didn't buy a compatible thermostat
2) You didn't hook it up correctly
3) Its defective

My guess is the likelihood of which issue it is is in the order I presented above.

Sorry I cant give more specific help.

thunderhead 06-19-2009 02:34 PM

The new tstat is actuallythe old tstat that the installers took out when they replaced the furnace. According to the instructions it is compatible with the new furnace. I dont know how I could have hooked it up wrong, but I am no expert either so it may be wrong. There are only fiveterminals on the tstat, R,W,Y,G and one that is marked Rc. The Rc is the one I didn't use. Could that be it? TIA

Brik 06-19-2009 02:45 PM

could be - re-read the installation manual. If you dont have it look here

There may be, or need to be a jumper between R and Rc. Don't put a jumper in unless the manual says it needs to be there. Don't remove one unless the manual says to.

thunderhead 06-19-2009 02:53 PM

I just looked again, there is a jumper between r and rc. I looked the tstst up on the site you listed, it is not there. This tstat is about ten years old. On my way to work, will resume when I get home tonight. Thanks for the help.

SKIP4661 06-19-2009 03:47 PM

May want to check for a blown low voltage fuse on the furnace circuit board as a blown fuse will cause a continuous blower on some models. Also you will need to jump r to rc.

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