Honeywell thermostat RTH 7500 wiring ?

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Old 09-10-06, 08:52 AM
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Unhappy Honeywell thermostat RTH 7500 wiring ?

I'm replacing an old 9525 with a RTH7500D. On the old thermostat there was a wire connected 1st to Rc then running onto Rh. There was also 1 wire connected to Rc. How should these be connected on the RTH ? the latter's manual says not to connect more than 1 wire to each terminal.
RTH seems to work (e.g. fan and a/c work) but when it calls for heat the furnace doesn't turn on.
The old thermostat worked fine

I've obviously screwed up the wiring (again).

Any help would be appreciated.
 
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Old 09-10-06, 09:13 AM
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I googled your wireing directions and it shows a factory metal jumper between RC and R on the new t stat.

The reason why this is setup like it is, is so that the system can have two different power sources, if needed, one for the cooling and one for the heating system. The tstat gets its power from the cooling system.

If you had a jumper between rc and rh on the original t stat then you only have one power source for your 24 volt power.

Either put the little metal jumper back, or run a wire to rc another to RH and splice them together with a little wirenut with the red wire from the system.

On a side note, make sure your programming is correct for the type of heat you have.
 
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Old 09-10-06, 09:20 AM
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thanks for the speedy reply.

If I put the jumper back, which wire would I connect - the old Rh or Rc ? and do I just tape up the other ?
Can I make a jumper with some excess thermostat wire ?
 
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Old 09-10-06, 09:52 AM
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I am now confused. I may have misread your post. Did you have two seperate wires, RH and RC , or one wire and a jumper between RH and RC?

Yes, a short bit of scrap wire is perfect for this.

If the little hole has a metal clip and the wire wont go in easy, loosen the screw, and then use a paperclip or sewing needle to bend the little clip out of the way.
 
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Old 09-10-06, 01:54 PM
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actually 1 wire (red) from the wall was looped around Rc and continued on and was connected to Rh. Another wire (black)from the wall was also connected to Rc.

On the new tstat I connected the red wire to the new Rc; and the old Rh (black) to the new R, however the furnace won't come on.

I have a sneaking suspicion that I should jump the new Rc and R and connect the red wire to either Rc or R - the remaining black wire would have to be taped and left unconnected to anything.

Does it matter whether I connect the red to the new Rc or R ?

Thanks for your patience.
 
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Old 09-10-06, 03:20 PM
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Not sure if you need the black or not, but why not hook it up the way it was? Red and black to R with a jumper to RC. You could connect to either R or Rc if it is jumpered.
 
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Old 09-10-06, 03:32 PM
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I suspect a timer at the heating section, and the installer used the connection to get the constant power needed.

I too would hook the black wire back up the way it was and see if it works.
 
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Old 09-17-06, 09:29 AM
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Was power shut off to the furnace first?? If not check for a fuse in the furnace. 3amp or 5amp.
 
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