No power to Y1 - nest thermostat


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Old 01-11-20, 08:30 AM
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No power to Y1 - nest thermostat

About a week ago, I pulled the face off the thermostat to touch up the texture around it. When I put it back on, I later got a "no power to Y1 warning). I assumed I knocked the wire loose, but now I'm not sure if it's related at all or just a coincidence.

I disconnected all of the wires and reconnected them several times. It didn't work. I tried turning off the power to the furnace a few times. That didn't work. Then at night, the fan was on and wouldn't turn off, so I unplugged the furnace.

The next day, I tried reconnecting the wires while the power was off and then plugged it back in. Power was restored to Y1, so I thought I fixed it. Then about an hour later, I got the warning again.

This is 100% repeatable. If I unplug the furnace then reconnect the Y1 wire, it works for about an hour then gives me the warning again.

This makes me think there's a maintenance issue with the furnace. I'll have to clear a bunch of stuff out of the garage to get to it, so I haven't opened it up yet. Before I do, I was hoping to get a better idea what I should look for to troubleshoot it.
 
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Old 01-11-20, 12:48 PM
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It would be really helpful to see your wiring on the nest.
Can we assume there is no C connection ?
A Y1 loss means a break in the wiring somewhere from the stat to the contactor in the outside condenser.
 
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Old 01-11-20, 07:07 PM
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A picture of the nest

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Last edited by PJmax; 01-12-20 at 10:57 AM. Reason: imported/resized picture
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Old 01-11-20, 07:11 PM
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Here you go. Today is the first day Iíve been home for any extended period of time since it started acting up. It works fine for an hour or two at a time then gives the error code. When it give me the error, I canít control anything from the thermostat. I can only go through menues. If I unplug the furnace and plug it back in, it works fine for an hour or two again.
 
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Old 01-12-20, 06:45 AM
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Those wires need to be cleaned up and donít look fully seated in the terminals.
I donít like nor do I recommend the Nest. Lots of problems and bizarre behavior. Theyíve made me a lot of money as a service tech with their issues.
Youíll need a C connection even though Nest will say you donít. They are extra unreliable with no common wire.
 
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Old 01-12-20, 11:00 AM
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I agree with the C connection but apparently that stat was working fine in the past.
The nest gets its battery charge from R to Y1. If the Y1 line is broken it won't charge.
Y1 is the wire that goes to the outside A/C condenser.
 
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Old 01-13-20, 10:57 AM
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I should have clarified that this shot was taken before I re-connected everything. I removed the Y1 wire, then thought to take a picture to make sure I put everything back where it goes.

After taking the picture, I disconnected the wires, trimmed them and stripped them back a little before reconnecting everything. They're correctly seated now.

Regarding the AC condenser, There's a small breaker box out there with a large fuse in it. There's probably a proper name for it. I just don't know what it is. In the summer, the fuse will sometimes slip out slightly, cutting off the AC. I had checked that and it was tightly in place. Might I need to replace it?
 
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Old 01-13-20, 11:18 AM
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Control voltage will be fed from the air handler, where the transformer is located. The disconnect is just for line voltage to the outdoor unit.
If the fuse is loose enough that it falls out on its own, the disconnect needs to be replaced. Thatís a fire hazard.
Loose electrical connections can generate a huge amount of heat.
 
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Old 01-14-20, 10:39 AM
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Here's what it looks like. I'm pretty sure this is the problem. It had been below freezing the past week. Maybe the metal shrank just enough to break the connection. I'm getting power to the thermostat now that it has warmed up. Do I need to replace the box or just the fuse? Also, what is the fuse called so I have a better idea what I'm looking for.





 
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Old 01-14-20, 10:54 AM
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Those blades are burned.
The disconnect switch needs to be replaced. That appears to be a non-fused disconnect.
If you have a split system that’s likely not the reason your thermostat is having issues.
 
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Old 01-14-20, 12:25 PM
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Do I need to replace the entire box? Or just the fuse? The fuse I can handle. I'll need an electrician for the box.
 
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Old 01-14-20, 12:51 PM
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There is no fuse. Those are just blades to close the circuit.
You’d need to replace the whole box.
 
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Old 01-15-20, 01:59 PM
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Ok thanks. I'll get an electrician out to replace it.

On the thermostat, what else could be causing the power disruption to the Y1 wire? It worked fine for a day, but is doing the same thing now.

If I unplug the furnace and plug it back in, it works fine for an hour or two then gives me the no power to Y1 warning.
 
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Old 01-15-20, 02:05 PM
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Y1 can be disconnected due to a safety switch. One safety is in the outside unit that is triggered when it senses low pressure/temperature. Another safety switch is usually attached to the furnace/air handler's condensate overflow switch. When is the last time you had the system cleaned?
 
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Old 01-15-20, 03:45 PM
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I cleaned the filter in the spring. I havenít done any maintenance outside of that since I bought the house four years ago.
 
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Old 01-15-20, 04:22 PM
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Y1 can be disconnected due to a safety switch.
Exactly.

Just to describe how the circuit works. The nest "steals" power to charge by being inline in the Y1/cooling circuit. Refer to the diagram. The 24vAC comes into the nest on R. R connects to the internal battery. The battery needs a connection to C so by being inline it gets it's C from the air handler thru the contactor, thru the low pressure switch and to the Y1 connection. So as long as there is a wire in the Y1 terminal..... the charge is handled thru the Y1 line. If you have a low charge the pressure switch will open the Y1 circuit.

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When you add a direct C connection to the nest it no longer needs to steal power.
 
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Old 01-28-20, 11:42 AM
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Sorry for the late reply. Between work and family, I haven't had time to mess with this. But I'm home sick and trying to figure it out.

I opened up the furnace and cleaned it out. The filters were dirtier than I expected, so I thought that might have been the problem. It wasn't.

I tried to get the AC to turn on. It won't. So now I'm back to thinking the disconnect might be the problem. I'm having that replaced next week. Is it possible that's the cause? Or is there something else I can check?
 
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Old 01-28-20, 11:46 AM
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I also completely swapped thermostats from the upstairs unit to downstairs unit. Before I only swapped the faces. The upstairs unit did the same thing when I installed it and the downstairs unit worked fine upstairs, so the thermostat isn't broken.
 
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Old 01-28-20, 03:54 PM
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I would try running with the Y1 disconnected. Let Nest steal power from the furnace via W1. See what happens.

Also - when it stops what does the furnace LED show? Since power stealing on Y1 it could be Nest is confused and the actual symptom is R being disconnected due to safety switch.
 
 

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