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Old 09-12-2020, 06:36 PM   #1
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HVAC System Low Voltage Wiring problem


Hi folks! Looking for some help here. Have a home and the HVAC has acted strange since I moved in. I'm pretty good w/hvac controls but this is so buggered up I can't figure out what they were trying to do (they being the original installers). There is something called a "add a wire" component, which is supposed to add a common, but there already IS a common. Also, looks like Y1/Y2 connections are reversed. Any thoughts on this? Can i just remove the "add a wire"? And why is there a jumper between y&g? it's all so strange. All i wanted to do was plug in a dang Nest thermostat! This is a 3 heat, 1 cool heatpump system. Normal HP mode, electric heat, and LP furnace, plus AC.
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thanks,
-Pinto
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Old 09-12-2020, 06:47 PM   #2
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Re: HVAC System Low Voltage Wiring problem


The Nest is an extremely poor choice for a thermostat. Nasty little things that aren’t fit for a paperweight. Especially for a heat pump. Using one without a common or with an add a wire device is almost guaranteeing you’ll have a lot of problems.
They are likely trying to use the G as the common, and jumped Y to G terminal to do so.
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Old 09-13-2020, 08:04 AM   #3
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Re: HVAC System Low Voltage Wiring problem


Hi, not really familiar with Nest, but I don’t like this concept of Add a Wire, I would think the best place to start would be at the furnace control board and work back toward the Stat, definitely take pictures before you make any changes.
IMO I would choose a Honeywell RTH 6500 or 9500 series.
Geo
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Old 09-13-2020, 10:09 AM   #4
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Re: HVAC System Low Voltage Wiring problem


Better do a thorough check of the low voltage wiring, since you have 2 heat sources that can run together, and one that requires the heat pump to shut off.
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Old 09-13-2020, 10:24 AM   #5
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Re: HVAC System Low Voltage Wiring problem


So, you have a dual fuel setup (electric heatpump and LP propane backup)? If so, you need to know that the nest will turn off the heatpump when the LP furnace kicks in or you'll ruin the system.
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