A/C Compressor not running after installing new thermostat

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  #1  
Old 06-13-15, 06:59 PM
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Smile A/C Compressor not running after installing new thermostat

My old thermostat stopped working, so I purchased a new one with wifi to replace that. The old one was powered by two AA batteries. A green wire connected to G, a white wire connected to W, a blue wire connected to Y, a red wire connected to RC, and a red wire connected from RC to RH, a yellow wire was not connected to anything (see picture 1). Everything was working fine (heat, fan and AC).

I also openned the furnace and looked at the control board, and all wires are connected to terminals according to color codes, that is, green to G, white to W, yellow to Y, red to R and blue to Com (see picture 2).

The new Honeywell thermostat I bought is not powered by batteries, so it requires power from the C wire. So I hooked up the wires to the new thermostat according to the color codes (matching what is on the furnace board, also as instructed by the thermostat mannual) (see picture 3). This is different from the old one, this time, yellow to Y and blue to C. The thermostat is on, the heat works, but AC is not. The compressor unit outside the house is not running at all. But the blower is running and blowing normal air out. So I switched the yellow and blue wires on the thermostat, the thermostat is not even on.

I put back the old thermostat and connected the way it was, and A/C is working again. (the problem with the old thermostat is that the touch screen is not working, so can't change temperature setting).

What could be the problem? Thanks in advance.

Old thermostat wiring
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Furnace control board wiring
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New thermostat wiring
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  #2  
Old 06-13-15, 07:34 PM
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You cannot connect yellow to Y at the thermostat unless you also change the wiring at the furnace.

You obviously have a splice between the stat and furnace.

Post a picture of this splice for more assistance.
 
  #3  
Old 06-13-15, 08:07 PM
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It looks too complicated, can't tell what is what.

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  #4  
Old 06-13-15, 08:54 PM
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Turn off power to the furnace, fan out those connections at your splice, connect the unused thermostat yellow to the furnace blue (and a condenser wire).

Connect blue to Y at the new stat and yellow to C.
 
  #5  
Old 06-13-15, 09:00 PM
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It looks like you may have an additional splice behind the thermostat.

That looks like 14 gauge wire at your j-box. You have 18 gauge at the stat.
 
  #6  
Old 06-14-15, 02:59 AM
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What he has is a MESS !

With tstat wiring in the same box as the power wiring . I think .

If it were me , first thing I would do is get the tstat wiring out of the box with the power wiring . Then I would try to get it all , 100% color to correct color , if he actually has enough wires to do so .

If he really has a bunch of splices on the tstat wire , I would investigate the possibility of running new tstat cable / wire from the furnace to the tstat w/o any splices .

And I am still running an old Honeywell mercury bulb tstat that was used when I installed it . I do not need wifi to a thermostat . But , different strokes .

God bless
Wyr
 
  #7  
Old 06-14-15, 06:16 PM
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Thanks for all the advices. It sounds like that it is too much for me to handle, especially when power lines are involved. It would be better to leave these to the professionals. Thanks again for the advices.
 
  #8  
Old 06-15-15, 02:23 AM
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Turn the power off .

God bless
Wyr
 
  #9  
Old 06-15-15, 03:08 AM
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Some stats especially wifi recommend against having high voltage next to the stat wires due to interference.
 
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