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Heating & Air Conditioning DIY

thermostat help

2 years ago

Hello, I have a old thermostat that is hooked up to my radiator heat system. I’d like to put in a smart thermostat and I know I will need a C wire for power. The cable that is run to the thermostats has an extra wire but I am just not sure where to plug it into. The pic I attached is of the control board for my system. Can I power the thermostats from here or do I need to buy a power supply and run the c wire to that?

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Comments (3)

cobalty2004
2 years ago
Sometimes there is a spare wire that isn't needed that is part of the conductors in the cabling. Mine has this too. If its not used now, it probably won't be needed later.
mike_home
2 years ago
It appears this is a L7224U Oil Electronic Aquastat controller. I found the schematic but unfortunately there is no labeled C (ground) connection. The red and white wire near the top go to the thermostat. Even the R terminal (24 V) is not labeled. It is important that is verified before connecting to a WiFi thermostat. The polarity doesn't matter on a simple two wire thermostat, but if you wire it backwards on a electronic thermostat you could damage it.

There are some Nest models which claim to work without a C wire, but no guarantee it will. The best option would be to have a separate power supply.
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You have to consult the Trane documentation of 20+ years ago to figure out how the heat pump connections (B, X2, and T) work in the old system. Not all manufacturers are consistent on how these operate. The other interesting thing is that the heat pump works in either normal or emergency mode. The auxiliary mode is disabled. I don't follow how that works. The is only one R connection on the old thermostat. This would imply to me that the same transformer is connected to the boiler and both heat pumps. This seems strange but I guess it is possible. The other thing that needs to be done is to draw a wiring diagram. From that you can draw a diagram for the new thermostats. This can be done, but it is difficult to advise you without having all the wiring information. Do you have an idea how much money it costs to heat and cool the house? The numbers may inspire you to start planning for replacement equipment sooner rather than later.
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Straighten out the rat nest in front of Y & W then reshoot pic two or three. In two it appears white is going to R but in three red is to R and white is loose. As you dress wires try making it clear which brown jacket each wire comes out of. Neatly fold unused wires to side making it clear they are unused. To help you answer Weed's question take your choice of (A) turn the heat on,make certain heat is coming from vents then go outside to see if outdoor unit is running. (B) Shoot a close up of switch controls on face of OLD tstat.
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Here is the TX9600TS manual. You thermostat has a temperature swing setting feature. This allows you to set the cut in and cut out temperature delta. The default is 0.25 degrees, but it can be set as high as 2.25 degrees F. It is described on page 24, and how you can change it is described on page 26. Check to see what you setting you have. There are also additional settings that could cause the behavior you are seeing. Read the manual carefully. I suggest you make one change at a time and give it a day to see if has made an improvement. This is an interesting thermostat and it sells for $54 on Amazon. I don't recall ever seeing the swing feature on other thermostats, even those that are much more expensive. You may already have the best thermostat for what you want to do. The problem may be that at $54 it is not built as a precision instrument and it has limitations.
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wdccruise
2 years ago
last modified: 2 years ago
Look at figure 4 of the installation instructions. The two terminals to which you connect a thermostat are at the center-top of the drawing; they are not the row of screws in your photograph. Your system alone supports only a simple, two-wire thermostat (example: Honeywell CT50A).

-- amateur

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