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Conversion of mercury thermostat (Q539A1014) to digital (RTH6350D1000A) - help!

Conversion of mercury thermostat (Q539A1014) to digital (RTH6350D1000A) - help!


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Old 07-30-17, 07:34 PM
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Conversion of mercury thermostat (Q539A1014) to digital (RTH6350D1000A) - help!

Hello,

I tried to replace two rounded mercury Honeywell thermostats (Q539A1014) with a digital thermostat also from Honeywell (RTH6350D1000A), in a dual-zone house I just moved in, but cold air was not coming out of vents - only fan was working.

Details about my installation:
- Air Conditioner: Payne PA13NR04800G
- Gas Furnace: York G1UA048S21 (4.0T 21S HALF COIL CHAMPGN)
- Dual Zone module from Ultra-Zone (have no idea how that works, first time I live in a dual-zone home)

When I bought the two digital thermostats, I read the manual and couldn't find where to connect some of wires in the existing wiring (brown and white). I called Honeywell's support team and got this recommendation for the 1st floor thermostat (main controller):
[TABLE="class: grid, width: 500, align: center"]
[TR]
[TD]Wire Color[/TD]
[TD]Existing connection
(mercury)
[/TD]
[TD]Suggested connection
(digital)
[/TD]
[/TR]
[TR]
[TD]Green
[/TD]
[TD]G
[/TD]
[TD]G
[/TD]
[/TR]
[TR]
[TD]Blue
[/TD]
[TD]B
[/TD]
[TD]not connected (isolated)
[/TD]
[/TR]
[TR]
[TD]Red
[/TD]
[TD]R
[/TD]
[TD]R
[/TD]
[/TR]
[TR]
[TD]Yellow
[/TD]
[TD]Y
[/TD]
[TD]Y
[/TD]
[/TR]
[TR]
[TD]Brown
[/TD]
[TD]O
[/TD]
[TD]O/B (Bottom)
[/TD]
[/TR]
[TR]
[TD]White
[/TD]
[TD]W
[/TD]
[TD]AUX (Bottom)
[/TD]
[/TR]
[/TABLE]

After I turned it on, only the fan was running, no cooling. House's temp was increasing gradually today and wife asked me to put the mercury thermostat back. I left a digital one installed upstairs (2nd zone, only 3 wires to connect: red, yellow, white) and it seems to hold well.

I also set up the advance settings on the main thermostat as follows:
Function 1: 0 (Heating & Cooling)
Function 3: 0 (Gas or oil heat)
Function 5: 5 (Gas or oil furnace)
Function 12: 0 (Manual changeover)

Apologies for the long post, but I thought providing a good amount of information upfront would help, and would appreciate any help here on how to make cooling works with the new thermostat (or suggest a better one). I have the old one back and things are working fine, but really want to get rid of the mercury thermostats.

Thanks!
PapaBearCT
 
  #2  
Old 07-30-17, 09:36 PM
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It looks like you will need to add a double pole double throw relay and some female spade connectors next to the zone control board or get a different stat for zone 1 so that it can properly control your zone system



That zone control board requires both O and B at the zone 1 stat connections to control system mode.

Name:  EWC Zone control w Honeywell OB stat.jpg
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Even though you do not have a heat pump, zone one would need to be configured for heat pump operation to utilize the reversing valve terminals.

O = cool mode / and B = heat mode.

The zone one thermostat is the master stat and it will control if you are in heat or cool mode.




 

Last edited by Houston204; 07-30-17 at 10:22 PM.
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Old 07-31-17, 05:28 AM
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Thanks for the clarification about Ultra-Zone, Houston204.

Both zones work properly with the existing thermostat (mercury), but I wasn't counting on tweaking with the ultra-zone module to make the digital thermostat working on zone 1. This may become a larger project than I expected.
 
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Old 07-31-17, 01:29 PM
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The Honeywell TH4110D would control zone 1 without modifications.
It has separate O and B terminals and it is able to control a single stage heat pump with W energized for stage 1 heat. ( The heating control wont be off by 2 degrees in your application like the TH3110C)
 
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Old 08-03-17, 06:57 AM
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Thanks for the help. I installed a TH4110D and it works really well.
 
 

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