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Old 06-12-2014, 11:51 PM   #1
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Help with new t-stat (B, E, R/H)


Ok I have a HVAC unit and I am replacing the t-stat.
Here are the current wire hookups and there discription on the old t-stat (Robertshaw 9420).

C-Blue ~24v Com
R-Red ~24v Transformer
Y1-Yellow ~Compresser Relay (Stage 1)
E-Black ~Emerg Heat
W2-White ~Aux Heat Relay (Stage 2)
G-Green ~Fan
B-Orange ~Heat Active Reversing Valve
Unused:
L-N/A ~System Monitor LED
Y2-N/A ~Cooling Relay (Stage 2)
O-N/A ~Cool Active Reversing Valve

Here is the termanals on the new t-stat (EcoBee) and my assumed wires:
Y-Yellow ~1st Cooling
W(O/B)-Orange ~1st Heating (or Changeover)
G-Green ~Fan
W2(AUX)-White ~2nd Heating (or 1st Aux Heat)
R/H-Red?? ~Heat transformer return
R/C-"" ~Cool transformer return (Jumpered to R/H by default)
ACC1-Black ~1st accessory relay (Emerg Heat)
ACC1r-Red ~Jumpered for power
ACC2-White2 ~2nd accessory relay (Dehumidifier)
ACC2r-Red2 ~12v from Dehumid relay(+)
ACC3-White3 ~3rd accessory relay (Humidifier)
ACC3r-Red3 ~Jumpered for power
IN1(+)-N/A ~Alt Dehumidifier
IN1(-)-N/A ~Alt 12v from Dehumidifier relay(+)

I'm not sure about the "B-Orange~Heat Active Reversing Valve", I know that messing this up can ruin your comp. What should go in R/H(&R/C) just 24v, or am I missing something? Also where should I put the Dehumidifier? The Dehumid has its own 12v DC relay for 120v power, so I know I don't want to send it 24v AC, but should I use a dry contact (IN1), or an accessory slot (ACC2)?!?

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Old 06-13-2014, 05:39 AM   #2
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Help with new t-stat (B, E, R/H)


Is it battery only operated?

The orange that is on B of old stat, goes to W/O/B of new stat. new stat has to be told to energize it in heating mode. Connect your dehumidifier to dry contacts.

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Old 06-13-2014, 08:33 AM   #3
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Help with new t-stat (B, E, R/H)


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Originally Posted by beenthere View Post
Is it battery only operated?

The orange that is on B of old stat, goes to W/O/B of new stat. new stat has to be told to energize it in heating mode. Connect your dehumidifier to dry contacts.
No, its 24vac, I assume that it's fed from the 24v transformer (old C & R). sorry, I forgot to mention that. That's where some of my confusion concerning R/H came from, do I need to jumper between Red on R/H & 24v AC input?
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Old 06-13-2014, 06:47 PM   #4
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Help with new t-stat (B, E, R/H)


Would need to see the wire diagram/instructions of teh thermostat to say for sure.
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Old 06-13-2014, 07:12 PM   #5
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Help with new t-stat (B, E, R/H)


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Originally Posted by beenthere View Post
Would need to see the wire diagram/instructions of teh thermostat to say for sure.

ecobee[DOT]com/wp-content/themes/ecobeev2/files/manuals/IMR1-290611_ENG_V23web.pdf

^^^Install manual - ecobee
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Old 06-13-2014, 07:31 PM   #6
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Help with new t-stat (B, E, R/H)


Okay. Yeah, the R and C are connected to the R and C from the transformer. And you will need a wire from R to RH and the jumper from RH to RC.
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Old 06-13-2014, 08:02 PM   #7
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Help with new t-stat (B, E, R/H)


Great, thanks for all your help!
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Old 06-14-2014, 12:23 AM   #8
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Help with new t-stat (B, E, R/H)


Ok, I think I'm all up and working. Had a small problem with the 24vac "RETURN", I mistakenly assumed the 24vac FEED (+) would be the main. Apparently HVAC systems switch on the neutral (BIG no-no in the standard AC/DC world I'm used too).

I have cool air flowing and have dropped 3-deg in the last 30 min or so. YAY!
Now I just wait until winter and see if the heat, Aux heat, Emrg heat, and Dehumid are working. ;-P
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Old 06-14-2014, 05:15 AM   #9
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Help with new t-stat (B, E, R/H)


Technically, it has no true + or -. Also no neutral. 24 VAC on an HVAC system has a common.

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