Whalen mercury thermostat to Nest learning (Gen 3)

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Old 08-18-18, 06:14 AM
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Whalen mercury thermostat to Nest learning (Gen 3)

Hi, new here, seeing alot of useful information so I figured I'd ask about my current project I'm working on. I'm also new to electrical work and don't have much experience for this field.

We are in a multi-unit condominium which has an old mercury Whalen T834A 1667 thermostat and want to upgrade this to the Nest learning thermostat, 3rd gen. We have already purchased the Nest.

The issue comes when taking off the covers, the base (8551 Q634G 1074) there are only four wires: R, G, Y, and B. I am at a loss for finding exact manuals and what each wire would represent. Really looking for where to correctly install each wire on the Nest system as there's no W or C wires on our current thermostat.

Any help or guidance would be appreciated, pictures below.
Cover
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sub-base with model number T834A 1667
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Base (model Q634G) showing only R, G, Y and B wires.
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Last edited by PJmax; 02-13-19 at 07:56 PM. Reason: resized pictures
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  #2  
Old 02-13-19, 06:59 PM
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Did you figure this out? I am looking for answers too. I have something that you can try if you still have not hooked it up
 
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Old 02-13-19, 07:51 PM
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Welcome to the forums.

Looks like I missed a thread.
What can I do for you K ?

The OP's system is 24vAC.
The nest would be wired............
R - Rh
G - G
Y - Y1
B - O/B
 

Last edited by PJmax; 02-14-19 at 10:51 AM.
  #4  
Old 02-14-19, 06:42 AM
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I just noticed that OP has 24v system. I have Whalen 4-wire 120v unit. I am looking for directions to convert to 24v and wire Nest

I have Y-Blue wire connected to Cool, W-Yellow wire connected to Heat, G1 and G3 terminals with Red and Brown wires for 2 speed fan controls
 
  #5  
Old 02-14-19, 10:08 AM
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Using a Nest or other 24vac thermostat with your system will require relays with a transformer. Not for the faint of heart.

Post pictures of what you have. Model numbers of the hvac unit might help.
 
  #6  
Old 02-14-19, 11:33 AM
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Here you go, unit wiring and current RAB20 thermostat. Note: that Black L1 is not used in this thermostat but I think there is a black wire buried behind it.
 
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Last edited by Kolyan2k; 02-14-19 at 12:18 PM.
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Old 02-14-19, 11:39 AM
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Black is the common. It would have to be in use.

RAB20

Black to red is fan low.
Black to brown is fan high
Black to yellow is heat.
Black to blue is cool
 
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Old 02-14-19, 12:22 PM
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No L1 (black is not used). I believed old 1970s thermostat had L1 but RAB20 only uses 4 wires. I spoke with Whalen and they said L1 is not needed because the way system is wired W and Y are inputs and get 120v depending on seasonal switchover
 
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Old 02-14-19, 12:28 PM
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Something is missing. Your system diagram and your thermostat diagram both show the use of an L or hot wire. If there is none..... then there is nothing for the switches to switch to.
 
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Old 02-14-19, 12:33 PM
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I am not sure what to tell you......Its confusing for me as well. Whalen support said I need to rewire the system so that Y and W are outputs and L1 is input. I will open up the thermostat and check whats going on with wiring behind it. I also dont understand how previous thermostat worked with L1 and RAB2 works without it
 
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Old 02-14-19, 12:45 PM
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There is black and white joined together behind the thermostat
 
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Old 02-14-19, 01:32 PM
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Spoke to Whalen again, was told that black L2 is sending the power to Aquastat through the white wire and power is coming back through Y W. and That it still need some internal rewiring in order to install anything else because all modern digital thermostats must have L1 and N as 120v input and Y and W outputs 120v
 

Last edited by Kolyan2k; 02-14-19 at 01:54 PM.
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Old 02-14-19, 01:39 PM
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L1 is neutral..... so yes..... the neutral is connected to the aquastat. Now you need L2/120v to Y or W to open the valve. I'm afraid without a clear wiring diagram.... we aren't going to be able to help you.
 
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Old 02-14-19, 01:59 PM
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Here is what Whalen sent for a different unit but they told me the idea is the same.

I made a mistake above....just to be clear L2 is the black wire and its connected to white wire inside the thermostat with wire-nut. Whalen said that L2 is sending power to Aquastat through that white inside the Tstat, then Aqustat is sending power to thermostat though Y-Cool and W-Heat

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Last edited by PJmax; 02-14-19 at 03:17 PM. Reason: resized/cropped/ehanced/reoriented diagrams
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Old 02-14-19, 03:01 PM
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Pictures of the actual wiring would help. Need to know how many wires and any extras.

Question is how good are you at wiring and relays? Is this a rental where you can't make permanent changes?

Similar discussion here: https://www.doityourself.com/forum/t...-learning.html
 
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Old 02-14-19, 03:18 PM
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That diagram is exactly the way the system would be wired if you were using a 120v line voltage digital thermostat. That diagram shows a neutral which we don't need but it also shows an active hot wire.

The text part is confusing and I'm muddling over it.

Also..... I will be making this its own thread.
 
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Old 02-14-19, 03:42 PM
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The actual wiring is above. Diagram is straight from the unit. Now at some point when I replaced old thermostat Whalen people told me to wirenut black and white together in order to make newer RAB20 to work. Long time ago I tried to install fan coil digital tstat but it didn't work (I forgot why) and now they are telling it's also impossible to install anything else unless I rewire the internals similar to what I attached in last post
I can rewire it myself, but I guess I don't understand why my L2 120v is connected to white wire that I suppose feeding power to Aquastat.

What if I disconnect L2 from that white and send L2 power through Y and W? Does that make sense? Why do I need to rewire the internals?
And if I do need to rewire the internals, does in make sense to disconnect black from that relay/bypass cap it, then locate some white (or grey as they say) wire there thats currently sending power to Aquastat and wire that in along with all Neutrals to create Common?
 

Last edited by Kolyan2k; 02-14-19 at 05:34 PM.
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Old 02-14-19, 05:28 PM
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PS thanks for that link, very useful if I ever figure out how to convert the unit to take digital tstats
 
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Old 02-16-19, 06:38 AM
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Planning to take out the internals tomorrow and check out the wiring. I think i get that wiring modifications procedures, except for step 8. Anyone can explain what's they want me to do?

Step 1 to remove black and grey from relay
Step 2 cap black and connect grey to Neutrals (which I don't need for nest)
Step 3 cut white going to fan motor
And then I am lost

Also just so you understand, there are no control boxes there need to remove the entire fan motor assembly to gain access to wiring and I won't have heat, that's why I am asking many questions before. It's a pita
 
  #20  
Old 02-17-19, 01:32 PM
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Ok. So I opened up the unit and there are no relays there like Whalen support said. I am also not sure what that Face & Bypass damper motor is, its not there either. This is the wiring that I saw, and there is no access to that Aquastat....I am guessing its not meant to be serviced. And whats the purpose of that Aquastat, cant I just turn fan on and off and bypass that thing?
 
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Last edited by Kolyan2k; 02-17-19 at 02:00 PM.
  #21  
Old 02-19-19, 06:53 AM
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Am I at least correct that if aquastat is not needed in my setup and I just need to operate 2 speed fan, then all I need is that 4 relay board for $8 bucks, 120 to 24 transformer, then wire red from transformer to Nest Rh, 1 speed to G, 2nd speed to Y1, and Common from relay is not even needed ?

Edit: Whalen support that that aquastat is needed and system needs to be rewired according to diagram then sent
 

Last edited by Kolyan2k; 02-19-19 at 08:44 AM.
  #22  
Old 02-27-19, 08:19 AM
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So I was able to replace my RAB20 tstat with digital unit and none of the rewiring crap I got from HVAC people and Whalen support was needed, that old Aquastat wasnt needed either. As far as Nest, I just don't see it happening, I mean somehow Nest needs to know when it's heating or cooling season and unless Nest supports some sensors it won't work as far as I understand.
 
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Old 03-09-19, 04:46 PM
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Installed Nest on another unit. Works fine too except that it reads +5f then current room temp. I would've installed Ecobee but it doesnt support 2 speed fan
 
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Old 03-10-19, 03:27 AM
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Apparently it's a known issue with nest and been going on for a few years now. Thinking about ecobee now, this 5 degree temp difference is ridiculous, and there is no way to adjust it
 
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