A/C won't shut off if set to On, but if set to Auto, works properly


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Old 07-26-12, 08:14 AM
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A/C won't shut off if set to On, but if set to Auto, works properly

Hi All,

Here's my scenario. Woke up this morning and the house was cold, too cold. T-stat said the temp was 67, but was set to 72. The fan was set to on. I expected to hear the furnace fan, which I did. Went outside and found that the a/c was still on. And there was a small amount of ice build-up on the line. Not good. After some testing I found that it (the a/c) works properly when set to Auto, but just stays on when set to On.

A little history... Over the last 3 weeks I have blown 2 fuses. (my system only has a fuse at the furnace, none outside at the a/c unit) This past Sunday I blew another one and the a/c unit would no longer come on, even with a new fuse.

So I called out a pro. He noted a short in the system and replaced the wire (with several wires inside it) that goes from the furnace to the outside a/c unit. That "seemed" to fix the problem. The a/c was back on and the house got cool. Woke up the next morning the house was too cool! Could not get the a/c unit to shut off, no matter what I did to the t-stat or furnace. Only thing that would shut it off was the circuit breaker. Called the pro back out and he said "oops, my bad. wired it wrong". He moved one of the wires on the furnace circtuit board to another screw, and that was that. It appeared to be fixed. It came on and off as it should, based on the t-stat settings. However, we only tested it in the Auto setting.

I generally leave our t-stat on the On setting, so I changed it to On at some point yesterday. All seemed fine until this morning when it was too cold again. And as I mentioned, the a/c unit was still runninng. I switched it back to the Auto position, and it's now working as it should.

I don't want to call this guy out again. I don't think this is a bad contactor issue since it does cylce on and off properly in Auto mode...I'm hoping this is a simple matter of moving another one of the wires on the furnace cirtuit board to a different screw and that he just didn't fully test his settings (or just doesn't know what he's doing).

Any tips or advice on how I can fix this myself? Thanks in advance for helping this doityourself.com newby!
 

Last edited by rbemiller; 07-26-12 at 10:41 AM.
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Old 07-26-12, 01:30 PM
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Yeah it seems like you could move a wire to fix it. Is it a heat pump? Seems like he wired y to g at the circuit board.
 
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Old 07-26-12, 01:43 PM
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Ok, looks like I'm on the right track. It is not a heat pump. Just standard a/c condensor unit. I'm not at home at the moment so I don't remember which wires are connected to which terminals on the circuit board. I do know that yesterday he only moved one wire, it was connected to a terminal which had another wire already connected to it, and he moved it to a different terminal that also had another wire connected to it. I know that's of little help w/out knowing the letters but thought I'd share.

I will take a look this evening, and if I can't get it right, perhaps I'll take a photo and post it here.

Thanks, and any other suggestions are more than welcome!
 
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Old 07-27-12, 06:13 AM
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So all I was able to do last night was take a couple of pictures. Daughter's birthday is today so we were busy getting ready for that.

Anyway, here are two pics that clearly show how he has the new wires connected. Can anyone confirm that this is incorrect and/or tell me how they should be connected?

Thanks!

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Name:  NewWires2.jpg
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Old 07-27-12, 11:54 AM
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I've done a little more digging today and from what I can tell, one of the two a/c wires needs to be connected to the C terminal, and the other should be connected to the Y terminal. So in my case, I just need to move the red wire from the Gc terminal over to the Y terminal, and leave the white wire on the C terminal.

Can anyone confirm if this sounds correct? Thanks!
 
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Old 07-27-12, 07:52 PM
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Anyone?... Bueller?...
 
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Old 07-28-12, 04:23 AM
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cant tell for sure, is the brown wire connected to Y on the control board and Y at the stat? If so, the yes, you are correct. If no, what does the brown wire connect to?
 
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Old 07-28-12, 09:12 PM
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Yes, I believe the brown wire is connected to Y and to the t-stat. Will give it a go and report back. Thanks for taking the time to post!
 
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Old 07-29-12, 08:56 AM
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Maybe there is a reason the guy who came out moved the wire. Maybe the fan connection on the board wasnt being told to come on even with the thermostat. You will find out if fan doesnt come on when you move the wire back.
 
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Old 07-31-12, 06:16 AM
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You would think a professional would have a reason for doing everything they do, but not in this case. I watched him do it, and in hindsight, I think his only reason was to get it fixed (or so he thought) as fast as possible.

Anyway, I was able to get it working properly! As I had guessed, I ended up needing to move the red wire from the Gc terminal over to the Y terminal, and leave the white wire on the C terminal.

Now everything works as it should. Thanks all for the responses!
 
 

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