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View Full Version : Installing a Honeywell RTH6400 thermostat


eliz310
Apr 25, 2009, 05:26 PM
We have installed a new thermostat. Could someone help me figure out if we have everything hooked up correctly? We have a Red wire connected to Rc with a jjump wire between R & Rc, Yellow connected to Yellow, White connected to white & blue (don't know what to hook it up to).

Joshdta
Apr 25, 2009, 06:01 PM
Still no luck. Sometimes blue is used one y instead of yellow. But you would have to look at the control board in the furnace to see what wires are connected where.

eliz310
Apr 25, 2009, 06:09 PM
Yeah, still no luck. There is a hold up somewhere, is it normal to have 3 wires connected instead of 4?

Joshdta
Apr 25, 2009, 06:20 PM
Do you not have a green?

Joshdta
Apr 25, 2009, 06:20 PM
Your really only need r w and y if you have a newer unit

eliz310
Apr 25, 2009, 07:04 PM
I'm not sure how old this unit is. Yes we have a green.

eliz310
Apr 25, 2009, 07:07 PM
We have blue, green, red, white. Sorry I'm an idiot, no yellow.

Joshdta
Apr 25, 2009, 08:06 PM
No yellow? Then hook blue to y and you should be fine.

T-Top
Apr 25, 2009, 08:13 PM
How did the old thermostat hook up. Did you have a R,W,Y on the old one?

eliz310
Apr 25, 2009, 08:33 PM
No Red, white, green & blue. We will try the blue in the y & see what happens!

Joshdta
Apr 25, 2009, 08:35 PM
It should work fine with the blue hooked to y, it is used that way anytime there is only 4 wires not 5

KISS
Apr 25, 2009, 08:35 PM
With 4 wires you can connect any two and note what happens:

X B G R W
B
G
R
W

1. nothing
2. Outside unit runs
3. Heat comes on and fan a little later
4. The fan runs

From that, we can figure out the colors.

eliz310
Apr 25, 2009, 08:43 PM
We got it! Thank you so much!

Joshdta
Apr 25, 2009, 08:47 PM
Great glad you finally got it. I was confused earlier I thought you had a yellow wire.

T-Top
Apr 25, 2009, 09:02 PM
One good thing you got going on with only three wires you have no common wire from the transformer so you can't blow or destroy any part. It may take six tries but I bet you get it.