Arcoaire furnace - nest and C issue

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Old 10-09-17, 11:11 AM
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Arcoaire furnace - nest and C issue

Hello all,

I realize this is a super old post, but I came across it by Googling for my fan control board part number, and -- shocker -- had the exact same issue as OP.

https://imgur.com/gallery/Su2us

Renting a town house with:
  • Honeywell TH5110D1006 thermostat
  • HQ1009836HW fan control board
  • Arcoaire RPJ II furance

Installed the Nest last winter with no C wire connected to the board with no problem. This spring, when the fan started short cycling due to the parasitic charging, I looked into the problem, saw that my thermostat wire was indeed 18/5, and determined where to land the C conductor (common side of the transformer secondary), but didn't have an appropriate size female terminal on hand, so I threw the old Honeywell back at it, tossed the Nest in a drawer, and forgot about it -- until a buddy got his, and I got the bug again.

Same thing happened to me as the OP -- blew the transformer. Entirely possible that I shorted something out at the thermostat, or that I grabbed the wrong side of the wrong side of the transformer secondary -- that doesn't matter. I replaced the transformer, confirmed that it worked with the Honeywell, and tried the Nest again. It didn't work. Nest support suggested that I had shorted out the base plate with all of my shenanigans, and sent another.

Same deal. Short cycles without the C wire, no power detected on either Rc or Rh when it does connect the wire.

I'm waiting on a new multimeter to arrive -- and yes, I let the magic blue smoke out of the last one on an unrelated project.

Any suggestions?

Separated from... air-conditioning-cooling-systems/c-wire-issues
 
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Old 10-09-17, 11:26 AM
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Welcome to the forums.

Based on the part number of the control board you left I'm not sure what the issue is. There should be a clearly labeled C screw terminal.

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Old 10-09-17, 11:51 AM
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Tried with the wire there, and going straight into the common on the transformer secondary, with the same result.

Glad I'm not crazy!
 
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Old 10-09-17, 12:23 PM
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On that terminal strip you will measure 24vac between R and C. If you don't get that at the stat location with the stat not connected you have a wiring problem. If you get the 24vac and it goes out when the stat is connected..... it's a stat problem.
 
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Old 10-09-17, 12:31 PM
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Thanks PJmax. Multimeter should be at the house tomorrow, will let you know what I find.
 
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