Nest Thermostat


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Old 03-15-12, 08:08 AM
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Nest Thermostat

Hi all, I placed an order for a Nest thermostat thinking that it was compatible with my current system. I'm not so sure now. I have a CTC 43503 thermostat which will be replaced by the Nest. Also, I have a Goodman PGB unit.

The CTC seems to be wired a bit odd since there are two wires at the O/B terminal. However, the orange wire isn't clamped behind in the terminal. It's kind of pinned underneath the screw head and on the "outside."

Was this just a bad wire job? Do you think the Nest is compatible?

Thanks!

Chad


 
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Old 03-15-12, 02:14 PM
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Chad,

In order to verify that the nest will work you need to do some investigating. What do the wires go to in your package unit outside? Your current thermostat seems to be improperly wired, but we dont know what the wires go to yet.

Connections in your package unit :

White - heat W
Green - Fan G
Yellow - Compressor (cooling) Y
Red - 24V power R
Orange - Y1 or economizer (optional on your unit)
Pink - Y2

Manual for your package unit : http://johnstonesupply9.com/TechDocs...O%20Manual.pdf

The nest does not require that you use the C terminal, however, I highly recommend that you do use it!

Some HVAC systems have high resistance in series with the Y1 and/or W1 power lines. This can prevent the voltage requirement from being met during Nest Learning Thermostat operation. In order for the Nest Learning Thermostat to be compatible with these systems, a common (C) wire is required.



I highly recommend using the C terminal no matter what type of system you have. The nest pulls power off the thermostat wires during a call for heating or cooling. I found this on a blog site about the nest.
Turns out Nest will pulse your furnace off and on just to recharge itself, which can cause problems with some furnaces.



Who wants that?! Here is another example The second day after I installed the two Nests, I heard a clicking sound coming from the heating ducts. Upon inspection, the downstairs furnace was working fine, but the upstairs furnace was making the clicking noises, which were resonating through the ducts. I fiddled with the thermostat; it wanted the furnace on but it wouldn’t come on. I turned the thermostat off; the clicking stopped. I turned the thermostat back on, and it turned on the furnace for about a minute, then the furnace turned off and went back to clicking. I fiddled with the thermostat for a while longer, and was able to provoke various permutations of this behavior, but not a working upstairs furnace.

I called Nest support, and got a really helpful and knowledgeable guy who suggested I swap the upstairs and downstairs units, to help rule out a problem with the thermostat itself. After the swap, I still had problems upstairs and not downstairs — apparently the problem is with the furnace, and not the specific Nest unit. His hypothesis was that my furnace was so sensitive to voltage that it would work fine if the thermostat just bridges the Rh and W wires, but if the thermostat pulls any power at all from those wires, the furnace relays get confused and start toggling instead of staying on. Just for fun, I measured the wiring at both thermostats with a multimeter and couldn’t detect much difference between upstairs and downstairs (in both cases, the multimeter saw 28 V across Rh and W with the thermostat detached and the furnace not running, and 0.485 A across Rh and W with the furnace running), but the Nest’s built-in technical details monitoring report claimed voltage dropped from 29 V upstairs when not running the furnace to 7.77 V when running the furnace (and compared to 9.19 V downstairs). Is that 1.4 V difference enough to explain why one would work and the other wouldn’t? I don’t know.

When I called back to Nest support with these results, the tech support guy said this sounds like a power stealing problem and the probable solution is to run a C wire. I asked why two nearly identical (same model, different size) furnaces that are only 3 years old would be different in this regard, and he didn’t really know.



SIMPLE ANSWER : ALWAYS USE C

I know this is a long post, but bear with me.

Help me to understand the hype of the nest thermostat. In my view it is not a good thermostat and is going to cause problems down the line. If it will work with your system (it should, just depends with your wiring) let us know your thoughts on it after you use it for a while. I just dont get the hype. There are other thermostats out there that can do more than the nest, they just dont "learn" your schedule. Programming can take as long as 10 min. on a normal thermostat. How much time are you really out by taking the time to program a good thermostat and then you dont have to ever worry about the program again.
 
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Old 03-15-12, 06:59 PM
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Another thing I noticed, there is no wire on Y. What is making the unit to turn on the compressor?

Like HVACtech said, need to get into the unit and take a closer look on this wire set up.
 
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Old 03-15-12, 07:05 PM
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Cool

Thanks. I'll have to get up on the roof when I get back from vacation and see how it's wired. The guy I bought the house from did a quick flip and remodel and I'm constantly finding little things like the poorly wired thermostat (e.g. no attic insulation).

FWIW, I tried Nest technical support a couple times and each time they told me something different. The first guy said it was okay, so I ordered it, and then I thought to check again and heard a different story.

So I originally purchased the Nest because of the gadget factor. It may not make a lot of sense given that the other options out there can do similar things with a minimal difference in effort, but that's what I wanted. I like the idea of being able to use it with my smartphone and the learning ability.

Whether it makes a huge difference is remained to be seen. I've been in the house long enough that I can compare year over year. That'll be the true judge for me.
 
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Old 03-24-12, 10:44 AM
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Inside the unit

I think I'm more confused than before. On the control board I didn't see the simply thermostat control wires labeled like inside the thermostat. I have a couple pictures that may help. Also, I the board is a 1068-400 and I found a manual for that. I'm just not quite sure what wires are doing what and how that relates to the thermostat. Thanks again!

http://www.dnmech.com/lit/Good_dsi_tp105.pdf



 
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Old 03-24-12, 02:04 PM
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I may have figured it out. The orange wire on the O/B is there because of the economizer and the blue wire is common. When I checked the board on the unit there was a wire plugged into the economizer so I'm assuming that it's being utilized.
 
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Old 03-24-12, 05:09 PM
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I still can't understand why O/B is used.. Y would of been used goign to the Ecno then the control there will decide to use outside air or compressor.
 
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Old 10-19-13, 11:18 PM
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So where do you connect the C cable in the control panel? I have the same issue with my nest and my panel is the same. Please help
 
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Old 10-20-13, 09:05 AM
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That unit is using the package unit body for 24VAC common.

However, the orange wire isn't clamped behind in the terminal. It's kind of pinned underneath the screw head and on the "outside."
 
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Old 10-20-13, 09:31 AM
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Hello Houston204,
So I need to connect the blue wire coming from the thermostat to any of this 2?
 
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Old 10-20-13, 10:07 AM
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I don't know what blue is connected to at your stat.

If blue is connected to C at your stat, connect the other end to the unit body at your package unit.
 
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Old 10-20-13, 10:32 AM
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Yes, blue is connected to my stat, so I just need to connect the other end of the blue wire to the package unit. Does it matter if I connect it to any of the 2 that you highlighted in green in the pic below?
 
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Old 10-20-13, 10:40 AM
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I'd connect stat common to the screw. The spade connector has enough wires on it now.
 
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Old 01-05-14, 02:55 PM
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Common Wire on Goodman HVAC CACF036a2a control board

Long story short, I have Nest Thermostat installed for past few months with regular R,Y,G,W wiring. Thermostat was working great until recent firmware update . New update requires more power and now I need Common or C wire to be connected for constant power source (24A). So I looked into my thermostat wiring, there was Blue wire for C. Tried connecting Blue wire to stat point C, but still no luck with Nest power drain. My bad luck, the other end of Blue/Common wire was not grounded. So I opened the furnace and checked the control board. With the help of this thread, I was able to hook it up to the Common Stat. I have attached the images for verification.
Houston, can you please verify the grounding/common wiring connection? I was not sure highlighted connector. I have highlighted stat wire and its connections (before & after). Please let me know if you need any additional info about wiring.

Thanks in advance.
 
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Old 01-05-14, 03:07 PM
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You have correctly connected to the common and your thermostat should work ok now.
 
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Old 01-07-14, 04:54 PM
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Thanks PJMax !

So it turns out that it was not issue with Nest or its firmware update but it was corroded gas sensor. Once HVAC Tech fixed that issue, my heater started working correctly. Nest also reports good power source since its using Common wire now.

Thanks !
 
 

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