HVAC / Wiring Guru's

[MichaelS]

Installed a Nest thermostat this morning, all went well except... one question I have - which isn't affecting operation at the moment, but I want to know why it was done originally and whether I need to correct it.

Standard wiring (conventional) for a 2 stage electric heatpump system (goodman if it matters). The wiring is generally pretty easy, R & Rc were jumpered as usually the case (Nest auto jumpers those, so no need to wire that special) however, Y2 and W2 were jumpered also (Heat secondary & Cooling secondary.) I did not jump that currently, but I am asking why it would have been done - should I do so again? 

New to heatpumps and multi stage heating and cooling combined, so I am out of my element. I couldn't find anything with 'the google' so I seek wisdom amongst y'all


Thoughts?

Thanks,
Michael

[daddo]

Not familiar with nest- too many complaints. However the wiring should be similar with the same type stat.

Do you have a 2 stage system with or without aux heat or do you have a single stage heat pump with or without aux heat strips?

W2 is second stage aux heat- goes to a relay.
Y2 is second stage contactor to run the second compressor or a staged compressor.

If you have a 2 stage system, W2 would cycle on by a specific time/temp fall below Y2. Y2 would cycle on first, then if it couldn't heat the space, then W2 would bring on the second stage aux heat.

Y1- 1st stage heat.
Y2- second stage heat.
W1- first stage aux heat
W2- second stage aux heat.
O/B- decides heat or cool outdoor energized relay on 4 way reversing valve.

You can see a conflict between W1 and Y2. If W1 is energized before Y2, you're using elect heat instead of the heat pump for second stage. However, if W1 is connected to the outdoor defrost board only, then W1 will only operate during defrost. Then there are outdoor thermostats to control the aux heat.........where W1 or W2 might not operate until a certain set temp outside.

Or hey- I could be wrong. I don't know much about Nest if I haven't mentioned that already.

[MichaelS]

No worries, you know far more than I on this one. I still cant figure out why the 2 would have been jumpered though on the old thermostat. Nest aside, I cant figure that out.

Michael

[daddo]

Perhaps humidity control of some type?  

[MichaelS]

I give up, spent nearly 2 hours with their engineers and short of tracing each wire back to determine why the (!@#U!@) the installer bridged the E and Aux/W2 wires, I cannot get the Nest to behave as it should and kick on the aux heating. Swapped back to the lame (but functional!!!) Honeywell programmed thermostat.

This is the 3rd gen, which fixed many of the issues folks associate with the first and second gen units, however my particular setup is not normal. 

I am going to peek at the wiring for the second zone (which has its own condenser/handler/etc.) to see whether it has this goofy arse jumper or not, and if not, use it there (as that room is not occupied often and having a smart thermostat there would be of considerable value...) however for downstairs, I'm calling it quits until I buy a new setup, which at 10 years on the goodman currently is probably not for another 5+ years (it sounds fantastic and the air handler is quiet as a mouse when it spins up)

Thanks again for the suggestions. 

michael

[daddo]

E/W2/Aux are basically the same- emergency/auxiliary heat strips.
 Being jumped should energize the strips during "emergency heat", "backup heat during heat pump operation" and "defrost cycle heating".

There should be at least two wires here (usually white)- one from the air handler and one from the outdoor heat pump (Unless they are jumped at the air handler).

There may be a time delay before they energize whether through the tstat or the relay that controls the strips. But should energize withing 3 minutes.  Also, it may be a "smart" thing, in the sense that the tstat decides if the backup heat is actually needed if it sees the temperature is not falling fast enough or the sequence of operations does not support it at that time.

One thing I have heard is that the Nest learns your habits and it is very very important to set it where you like it and "leave it alone" for several days to learn. Making drastic changes to the temps a lot during this time can confuse it and cause erratic operations.

If the strips are not working perhaps there is a wiring or control problem. I had a Ruud system 6 years old where the strips never worked from day 1 because the wires were never connected. For 6 years and several complaints every winter, no one caught it. It happens.

Do you have the "C" connected to the tstat? This common from the transformer may be required to power the tstat for certain functions..??

 I'm going to have to buy one and try it out- I should know more about these- or maybe not.

[MichaelS]

Lol, patience may indeed be the root of my issues with the Nest. Not sure (I didn't have the patience to wait 15 minutes per adjustement to see if it would work or not.)

It may have been hooked up correctly, but I can't say as the jumper at the tstat isn't documented anywhere I could find and the Nest guys were unable to troubleshoot remotely without knowing with certainty where the brown wire (which is the w2/aux in my case) ran to.

I was never able to get the Nest display to register / kick on the Aux heating though, no matter what I did to it - so, I assumed that the system was not functioning optimally. Plus it seemed to me that the condenser / first stage was running considerably longer than it had during previous nights with the Honeywell unit.

I just need to bring in a voodoo doctor
I may suck it up and hire a 'nest pro' and have them trace the wires and configure (via the pro screens) the device. I really would like it for the automated fan controls and efficiency aspects of knowing the environment... but my setup is a bit goofy (maybe?).

Best,
michael