New Thermostat - strange wiring?


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Old 06-16-17, 11:05 PM
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New Thermostat - strange wiring?

I am replacing my old thermostat with a new Nest, but the error code from the Nest says I am not getting anything from the Rh wire.
Now, the current thermostat still works, but I was hoping to get some optional blower control which the current thermostat does not have. After removing the old thermostat I found that my blower runs without anything hooked up at all. Nest diagnosed it as a faulty device from them, but I suspect there is something unusual with how the furnace was wired. Why else would the fan turn on the moment power was restored, even though the thermostat-side field wiring is not connected?

My furnace is a Carrier 59MCB060. The field wiring on the furnace side is Rh, W, G (Y is not connected). The field wiring on the old thermostat side was Rh (jumpered to Rc), W, G, and Y. The new thermostat is Rh, W, G, Y. I made sure to label and double-check the wires, so I know they were not mixed up.

This image has Rh plugged into Rc, which was part of the troubleshooting with Nest, but I was mostly using Rh.
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Old 06-17-17, 04:56 AM
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On the G terminal in the furnace there is a green and black wires. Trace the black wire and see where it goes.
 
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Old 06-17-17, 10:04 AM
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The black wire on the G and the faded red wire on the R lead go to my HRV.
That might explain the fan running instantly, if the HRV is set to control the furnace blower. I will experiment later and post the results.
But that would not explain the lack of power on Rh?
 
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Old 06-17-17, 10:47 AM
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Welcome to the forums.

As a test I would disconnect the HRV wiring and try it again.
You may need to install a relay on the HRV line.
 
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Old 06-17-17, 11:32 AM
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Since the Nest does not have a C connector it "power steals." On Y1 if connected, and if not, from W1. Disconnect Y1 and that should at least solve its power problem.
 
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Old 06-17-17, 11:41 AM
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@ Astuff.... I'm not following your train of thought here.

It should steal thru any available path. I'm envisioning a possible two transformer issue with the HRV.
 
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Old 06-19-17, 07:09 PM
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I took PJmax's advice and removed the HRV from the equation. Here is what I found today:
  1. I unplugged the R wire of the HRV. I tested it manually to confirm this was what turned the blower on, which was true. I connected the Nest and no change was detected, still no power detected on Rh.
  2. I unhooked the Nest and tried manually connecting the R and G wires to check if the blower came on from the thermostat side (see if maybe a wire was broken). The blower did turn on.
Nest diagnosed the problem as a bad thermostat base. They are sending me a new base. I didn't believe it at the time, but since connecting R & G does start the blower, I can't think of any other good reason it wouldn't work.
 
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Old 06-19-17, 10:32 PM
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This doesn't matter if the backplate is bad so just what I found out. The original Nest design wasn't designed to steal power through any available path. Instead mechanical switches that are part of the C and Y backplate connections determine how power stealing was routed. So if there is something in C it doesn't try W or Y. Only if both C and Y are empty will it try W.
 
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Old 06-20-17, 08:04 PM
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Ok.... so there was no C but there was a Y1 connection. Y was not connected at the furnace board but it was connected to the condensor. The contactor should have allowed it to steal on the Y line.

Defective base does make sense and I've been seeing it more and more in these threads.
 
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Old 06-21-17, 07:33 PM
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Doesn't look like there is an a/c condenser. Y1 was blue at the 'stat and coiled up at the furnace.
 
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Old 06-21-17, 08:27 PM
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Astuff is right, the Y is coiled up at the furnace side. We have no A/C so it is not functional.
 
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Old 06-21-17, 08:51 PM
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My bad.... I thought there was A/C in the mix. So it should not be connected at the stat.
 
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Old 06-22-17, 11:37 AM
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use the wire you connected to y1 as a common, connecting it to c at the furnace.

the nest is known to be a bad product and if it continues to give issues, you should return it.

ecobee3 and anything made by honeywell will be infinitely better. nest is an apple inspired product and they should stick to over-priced, disposable iphones and stop meddling in a market they have no business touching.
 
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Old 06-22-17, 09:19 PM
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meddling in a market they have no business touching.
People have said the same thing about Amazon and Walmart.

Honeywell is now offering better thermostats to compete with Nest and the like. Without that competition Honeywell thermostats wouldn't have the features they have today.
 
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Old 06-26-17, 07:26 PM
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PJmax wins it. After removing the Y wire from the thermostat end the Nest noticed the Rh power.
Thanks to everyone who contributed.
 
 

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