Please help decode this wiring mess in my A/C unit

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Old 06-24-13, 12:17 AM
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Please help decode this wiring mess in my A/C unit

I purchased a house, built in 2003 by a good builder. First thing I noticed when I took off the face plate on the thermostat is the switch is set for "gas" and not "electric" when I have electric heating and cooling. What's up with that? Doesn't that matter? The HVAC system is a lennox. I'm looking to replace the thermostat with a Honeywell programmable but it says I need a 24v constant "C" wire, which I cant find so I opened the blower panel and found this mess of control wiring. Photos here:
http://i41.************/30ikgus.jpg
http://i44.************/k4ds9s.jpg
at the thermostat I have:
G (fan control)
Y (cooling switch)
W (heating switched)
RH and RC are jumped with R wire 24v power.
Can anyone make sense of the wire mess inside the air handler?
One control wire goes to the thermostat, one control wire goes down to the compressor. I don't know which goes where. Some wires are twisted together with wire nuts and others go to the terminal strip. The thicker yellow wires are a float switch in the condensation pan which kills the unit on an overflow. Any clue on which one of these wires I can grab for my 24v "C" wire that I need to drive the new thermostat? There is a yellow wire that is not connected at both ends which should be hooked up to "C", but I have a blue wire in the air handler terminal strip hooked up to "C". That blue wire goes into one of the two control lines and I don't know which way it goes or where it connects. Anyway I'm open to suggestions,
Cheers,
X
 
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Old 06-24-13, 12:23 AM
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sorry images didn't go, I'll upload them again
 
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Old 06-24-13, 12:26 AM
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Sorry photos are attached now

Sorry guys, problem with the photos in the last one...here you go...
[ATTACH=CONFIG]14289[/ATTACH][ATTACH=CONFIG]14290[/ATTACH]
 
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Old 06-24-13, 12:42 AM
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Higher resolution photos for you guys

I was unable to upload quality photos from the websites. Here are some better photos Name:  pic1.jpg
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Old 06-24-13, 12:48 AM
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The C wire currently connected looks like it's for the compressor. You would just add another wire on the same terminal for your C.

Your thermostat is currently using blue for the Y terminal which should be yellow. If yellow is actually there it doesn't make sense why they didn't use it.

So just to confirm.....you have five wires at the thermostat. Is that correct ?
White
Red
Blue
Yellow
Green
 
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Old 06-24-13, 12:55 AM
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I found a yellow wire tucked behind the thermostat in the wall. It is not connected just sitting there and at the air handler end the yellow wire is just hanging there not connected. In the air handler picture you can just see the thin yellow wire bottom left near the red and blue. It's not connected and just sitting there. That would make a 5 wire run, 4 are connected, one is not. I can just add this yellow to the blue terminal for my 24v? I'm confused as to why the blue that is connected to the "C" terminal goes into a different bundle and the yellow from one wire is wire nutted with the blue from another line. The blue from the C terminal doesn't connect to either of those two.
 
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Old 06-24-13, 01:02 AM
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Correct, I have Green, dark blue, white and red (yellow is tucked in the wall) making 5 conductors. At the air handler end the dark blue (from thermostat) appears to tie to the yellow from the other cable. The light blue goes to the C jack and goes into the other wire bundle (along with the dark blue patch) which I assume goes outside.
 
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Old 06-24-13, 01:09 AM
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also is it safe to change the switch from gas to electric in the thermostat? I don't know why it would have been set that way or what that changes in the running of the unit.
 
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Old 06-24-13, 09:53 AM
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I would convert the blue wire that goes to Y on the thermostat back to the yellow it should have been and then use blue as the common.
 
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Old 06-24-13, 12:59 PM
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only thing is that it appears the blue wire from the thermostat is wire nutted to a yellow wire which appears to go to the outside unit. It goes into the other wire bundle. It doesn't connect to the terminal strip. Shouldn't it be connected there? The light blue which is connect to C goes back into the same wire bundle and appears to go back to the outside unit. The only wires from the thermostat which connect to the terminal strip are white and green. the rest are twisted to wires that go outside.
 
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Old 06-24-13, 01:13 PM
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The blue wire connected to C is for a/c. (Y goes straight to the a/c in your case)

All you need to do is connect the yellow wire to C at the air handler and t-stat. Colors don't matter as long as it's wired properly.
 
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Old 06-24-13, 02:01 PM
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ok thanks. That's what we have been talking about at work today. Not sure why they used blue for the Y line when yellow was there unless the yellow is broken along the line. I'll ring it tonight. The blue is wire nutted to yellow and goes outside. Thanks for the tips guys.
Cheers,
X
 
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Old 06-24-13, 03:39 PM
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I forgot to mention - the switch on the t-stat should be set to fossil fuel if the heat worked fine for years.

The fuel switch is only there for older air handlers which don't automatically bring on the fan when there's a call for heat.
 
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Old 06-25-13, 11:07 PM
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well I installed the new thermostat tonight, I connected the spare yellow wire to the C terminal at the air handler and connected it to the C terminal at the thermostat. It has 28VAC on it. I hooked up the wires exactly the same as the old one R (incoming 24v) W ( heat ) Y (cool) G(fan) and C (the new common line) anyway as soon as I flipped the breaker back on the fan turned on and ran instantly even though I have the system set to off and the fan set to auto on the thermostat. After a few minutes I started to smell the burning of the heater coil from the air vents. I switched the system from off to cool and didn't notice any temperature drop. I walked outside and the compressor was running, but the air from the vents was still hot. At this point it appears the heat coil and the cooling is running at the same time. I'm unable to stop the fan or the heat cycle even when I have the system set to "off" it's still running. I hooked back up the old thermostat with the same wiring pattern I used for the new control and now I have everything working as normal. I'm really stumped. The only thing I can think of is that "C" terminal strip is a jumper for the heat cycle and not a common 24v as it should be so no matter what I connect once I hook that wire up to my thermostat the heat coils run and makes the fan kick on at the same time. I'm up to 88degrees in here now so I'm on the old thermostat control trying to get out of this sweat box. Can anyone make some sense of what's happened? This makes no sense. I'm not an A/C guy, but I'm pretty sure the original wiring is messed up with the way it's acting.
Cheers,
X
 
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Old 06-26-13, 03:24 AM
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Your system and wiring are straight forward. Either the w
Yellow wire goes to something else or the wiring is spliced elsewhere or you have a bad thermostat. I'm meaning towards a bad thermostat.
 
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Old 06-26-13, 09:06 PM
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Resolved

I got it resolved. Hidden in the installer menu this thermostat was configured for heat pump and gas heating system, not electric causing the heat coil to fire instantly for whatever reason in all modes. Making the changes to 3 installer settings fixed the issue and its working as normal now. Why this would be released setup this way I don't know.
Cheers,
X
 
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