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Thermostat going 4 degress higher. Swing was set. Need wire help.

gsdk9
December 2, 2018
last modified: December 2, 2018

Hi,

Hopefully someone here can shed some light on my issue. I will give a little background on it first.

I have a Thermo Pride cma2-75n gas furnace. It was installed new for me some years ago.

For my central A/C the company installed a York D3NZ024N05606A, roof top a/c heat unit(unsure why but it has worked fine.


This past summer I had an a/c charge done and the tech said something about fans in the two units both running at the same time and they should not be and said "I changed some wires in the thermostat as it was wired wrong".


Now, I never had an issue until this winter when we started using the heat. The state that was on the wall would run for about 4degress over set temp. As I knew nothing about heating systems, stats or swing, I figured it was going bad. I replaced it with the same one that was installed and was sure to put the wires in the same spot the furnace guy did(I took pics just for a reference also to really make sure). Now the new stat did the same thing. So, I got another thermostat, we are on number 3 now. Same issue.


I followed instructions in manual to set the swing(.5 degrees) thinking that was the issue. Still running 4 degrees higher.(example: set to 68 shuts off at 72).


Again, I never had an issue until the wires were switched. Can this be the issue? I am not going to switch wires without knowing what I am doing, so asking for some help. Below is two pictures showing wiring at the stat and at the furnace. Some wires are labeled different colors(thats how they were). The red wire that you cant see the label is rc. Black wire is just disconnected.


New thermostat is Lux TX500u.

Thermostat has 5 wires hooked up, furnace has 3, I dont know where to look if you need to see other two).

I just want me furnace inside(not outdoor) my house working like it was. Can anyone help please?


Thanks.

P.S, I dont want to call the furnace company back at this point.





Comments (13)
  • cat_ky

    Who installed the units? I would call them. Best to have someone who knows the units and installed them come and take a look.

  • sktn77a

    A couple of observations:

    1. Just because the wire at one end is green doesn't necessarily mean the green wire at the other end is the same wire. I'd check continuity of all the wires.
    2. The black wire connected to Y1 is for a heat pump/AC - your thermostat can control a heatpump. Make sure all the settings are for a non-heatpump (gas) installation.
    3. The York D3NZ024N05606A is a gas package heat/cool unit. So it looks like you have two gas furnaces(?) That's a setup for problems.

    I'd definitely have the company that installed the rooftop unit come back, tell them of your issues and ask them to explain how everything is working while they fix the problem.

  • gsdk9

    Thank you for the responses.


    Yes two gas furnaces, the one outside with the ac unit does not get used. We didnt pick this unit, this is what they installed with no explanation why.

    I was trying to avoid having to call the company that has done all of the work due to having a fair amount of home damage done last time.

    I do not know how to check continuity.

    I was half tempted to put the wires back where they were originally(I have a photo of it)(would it hurt to try?) but not going to risk damaging something.

    I suppose my only option is to find a new heating company to check it all out, sounds like.

  • gsdk9

    If it was hooked up incorrectly would that cause the temperature to be so much off though?

  • weedmeister

    Take a look at those wires on the furnace in the picture. They should be solid, not stranded. I'm guessing the Y and Rc (which are stranded) go to the outside unit. And can I assume the outside unit does NOT have its gas hooked up?

  • DavidR

    > They should be solid, not stranded.

    Why do you say that? Because it might indicate a DIY or clueless installation?

    As long as the wire size (gauge) is adequate for the use, stranded vs solid wire makes no difference whatsoever. Both will conduct electricity exactly the same here.

    When I moved my thermostat a few years ago, I had a big box of CAT 5 Ethernet cable, so that's what I used. Works fine. Wire is wire.

  • ci_lantro

    The big reason to use solid vs stranded wire is that solid wire is easier to thread into those terminals. With stranded wire, there can be a problem if a loose strand manages to contact an ajacent terminal. More likely because the terminals in a thermostat are so close together.



    Just had a problem with our thermostat. It started running 2 degrees past set temperature. (I have it set for a 2 degree temp differential because the heater was constantly kicking on, running for just a bit and then kicking off...which was driving me nutz.)


    After a bit of sleuthing, I found that the caulking backer rod that I had shoved under an exterior door (across the room from the thermostat) had become unwedged and there was a significant draft from underneath the door. (The backer rod was supposed to be a temporary fix that I did a couple of winters ago but forgot all about it...) Once I got that hole plugged up (with a better temporary fix), the thermostat quit heating past set temp.


    I don't know for sure if the draft was the reason the thermostat got weird or if it was a coincidence.... Whatever, I did buy a new thermostat to replace the old one but haven't installed it since the problem seems to be resolved. Just tossing my recent experience out there as a potential cause because a new therm hasn't fixed your problem.


    (Yes, I know my thermostat is in a poor location and should be moved away from drafts from opening/ closing exterior doors. Just no good or easy place to relocate it to and it's a low priority problem.)


  • DavidR

    "With stranded wire, there can be a problem if a loose strand manages to contact an adjacent terminal."

    To reduce the chance of this happening, twist the small wires together counterclockwise (viewed from the wire end) after you strip the wire. That way, tightening them under the terminal screw will twist them tighter rather than untwisting them.

  • mike_home

    Can you post the photo how the wires were originally connected? This may give a clue as to what is going on.

  • gsdk9

    Thanks for the tip. I will redo the wires.

    I'll post a photo of the old one when I am by a pc.

  • weedmeister

    " Why do you say that? Because it might indicate a DIY or clueless installation? "

    No, because one set of wires goes to the furnace and the other set goes to the AC. Just wanted to confirm and all the wires going to the furnace were the solid set and hadn't been switched at the thermostat.

  • gsdk9

    Still looking for the old picture. The one I thought was it was after they were done, still digging.


    -unsure if I mentioned, after he switched or unhooked whatever wiring he said(could have been at themorstate or else where, unsure), when the A/C was run the fan in the furnace no longer would run(I thought it was suppose to), but again he said two were running. This heat issue has only started this winter since that was all messed with.


    -I did clean up the installed wires(frayed) and also installed new Duracells.


    -pretty sure after 3 new thermostats, the problem isn't the thermostat itself (as in set wrong or defective).

    Is there anything at the outdoor unit I should check. The indoor furnace is right behind the wall the themosate is on, if I had to run new wire it is easy where I can handle it.


    Again, I truly appreciate the help.

  • SaltiDawg

    Get the guy back that swapped the wires.

    "I figured it was going bad. I replaced it with the same one that was
    installed and was sure to put the wires in the same spot the furnace guy
    did(I took pics just for a reference also to really make sure). Now the
    new stat did the same thing. So, I got another thermostat, we are on
    number 3 now. Same issue."

    What did Einstein say about the definition of insanity?


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