Accidentally crossed wires on thermostat


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Old 12-27-21, 03:58 PM
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Accidentally crossed wires on thermostat

Hello,

Old house didn't have c-wires, new one does and while installing a smart thermostat, the metal in the drill head cam in contact with a few of the wires and caused a few sparks. Yes, potentially costly mistake.

Want to see if and how I can troubleshoot this before having to call a electrician. My setup is:
  1. Brand new construction up to latest Atlanta, GA code.
  2. Multi zoned single unit ac/heating system using dampers (see picture). Master one box doesn't appear to be getting power nor are the damper lights on (though I can't remember if they were originally on before I started)
  3. None of the circuits on the main box appear tripped. No main power switch.
  4. Since all 3 thermostats (one on each floor) is out I'm thinking this is not a local wire issue but something more central.
Happy to answer any other questions but I thought new homes were built to prevent major system damage from this exact scenario. Wondering if this indicates some wiring issues.

In any case, anything I can check on my own before calling in help?







 
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Old 12-27-21, 04:11 PM
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Is that a ZoneFirst H32P zoning board ?
 
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Old 12-27-21, 04:14 PM
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Yes, H32P
 
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Old 12-27-21, 04:21 PM
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Here's a PDF manual for the H32P

If the system/status LED's at the top aren't lit.... the board is not being powered.

Check the blue and black wires (R and C) on the right side for 24vAC.
If that is not there..... you need to locate where that source or transformer is.
There is no fuse on the board.... just a thermal limiter that should have protected the 24v source.
 
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Old 12-27-21, 04:36 PM
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Which wire got shorted?
The ones going to thermostats? or the one going to HVAC?

I see PTC (basically a re-settable thermal fuse) on control board, but if it was shorted before going to the board, that will not do any good.

HVAC usually have fuse on their control board.
From what I understand of that zone controller, it gets power from HVAC or secondary 24V transformer. Your picture shows 24V terminal is connected to the same cable running to HVAC. So, it probably is getting power from HVAC's R an C terminal.

Check HVAC's control board for blown fuse.

If it has external secondary transformer, check output voltage on it and replace if you don't have output. Internal fuse probably blew.

 
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Old 12-27-21, 04:41 PM
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Okay, H32P definitely not getting power. The black and blue cables exist but don't look burned out. I followed the black /blue to the heater/fan unit but not sure what I'm looking for. I do see a single 5 fuse but how can I tell a good one from a bad one?



 
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Old 12-27-21, 04:50 PM
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It definitely is being powered from HVAC's transformer.

I do see a single 5 fuse but how can I tell a good one from a bad one?
It is automotive ATC fuse. You will be able to see blown fuse by looking in the middle. If there is broken wire, it is blown.

Also, you will have to close blower side of HVAC before you get power. There is a safety switch that kills AC power if blower door is open.


 
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Old 12-27-21, 04:56 PM
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It should not be powered from the system transformer.
A zoning panel with powered dampers needs its own standalone 24vac 40va transformer.

Is that the brown fuse in the air handler ?
That's not OEM. Someone had the forethought to install it.
 
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Old 12-27-21, 07:55 PM
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Okay folks, I couldn't tell whether the fuse was blown or not because it didn't look like any fuse I'd seen in the past - it has a wired "ball" in the middle. Anyway, a quick trip to AutoZone for a new 5A Fuse and presto - we are back in business. Now have power to the zoning board, all thermostats and the AC/Furnace kick on. Thanks for everyone's help!!

@pjmax - You mentioned the zoning board should not be powered by the HVAC. Is this just a best practice or actually an issue that should have failed inspection (again, this is a brand new home)?

 
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Old 12-27-21, 08:43 PM
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I checked the install manual.
One does come with the zone board and is shown in the connection diagram.
They do not specifically state to use a separate transformer.

I use a separate transformer with zoning boards but it could be called best practice.
Not likely something an inspector would look for or comment on.

 
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Old 12-27-21, 09:25 PM
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That's not OEM. Someone had the forethought to install it.
I'm not a professional HVAC technician, but I have seen this sort of setup before. It was heat pump system with electric backup heat. There is no control board inside. Just transformer, contractors, and time delay contractors just like what the op has and it was OEM setup.
 
 

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