Hot Topics: WiFi Thermostat Doesn't Match Old Wiring Hot Topics: WiFi Thermostat Doesn't Match Old Wiring

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Upgrading to a smart, WiFi thermostat is a good way to save some money and plant your feet in the 21st century. But connecting brand new tech to old HVAC can be a puzzle. The Forum has the key to bring you up to date.

Original Post: Installing a new wi-fi thermostat with no C terminal - Goodman furnace

JESUSELDYABLO Member

Hello, I hope somebody in this forum can help me solve my issue. I am trying to replace my old thermostat with a new wi-fi Honeywell tt. The problem that I am encountering with my gas furnace (propane) is that it does not have a C terminal like the new furnaces do. I have the extra cable but I do not know where to connect to. From what I’ve been reading it looks like this terminal might be near or on the transformer on the switch board. (That's what I think but can't confirm since the info that I have found is not particular to my unit.) Can someone please guide to get this done correctly or is this unit so old that will not be compatible with my new tt? I am attaching a few pics of the old tt and the current set up on my furnace.

Goodman model #: PGB30075-1

Thermostat model: Honeywell RTH9580WF

Hot Topics-WiFi Thermostat Doesn't Match Old Wiring

Highlights from the Thread

PJmax Forum Topic Moderator

Welcome to the forums.

Is this a packaged unit? A/C and furnace are in an outdoor unit?

My service info shows your unit as a packaged system and that there is a terminal strip like in the diagram below. The manual also shows that your unit used ground for the C connection which means you can connect C to a clean location and screw on the unit.

You can confirm with a meter that you have 24vac between ground and the R connection or red wire.

JESUSELDYABLO Member

Thank you for the quick reply.

Yes, this is a packaged unit as you call it. I don't see any diagrams but are you saying that all I have to do is find a clean spot and attach the blue wire with a screw and that should give me my common connection? I hope I am making sense. I am attaching a few more pics that I just took just in case that helps.

PJmax Forum Topic Moderator

Wow.... I guess we're even. I forgot to post the terminal block that the manual shows for your unit and you didn't post any more pics.

Hot Topics, WiFi Thermostat Doesn't Match Old Wiring

JESUSELDYABLO Member

Yes, you are completely right, I also forgot to attach the pictures, just realized that my phone won't attach the pics for some reason.

I just looked at your diagram and it does not look like my unit. I don't have those terminals. I think the pics would help see that.

Hot Topics, WiFi Thermostat Doesn't Match Old Wiring

PJmax Forum Topic Moderator

Ok... no problem. Some manuals cover many models and don't differentiate between the series.

In the pic below... the grays are the common wires for your unit. It looks like the two gray wires are connected together and then to that wire that goes to ground. You can use that screw for your C connection.

Hot Topics, WiFi Thermostat Doesn't Match Old Wiring

JESUSELDYABLO Member

Thanks for the help, I really appreciate it. I do have another question. My blue wire does not reach all the way over there. Is it okay if I get another wire, tie it with a wire nut and run the new wire all the way there?

PJmax Forum Topic Moderator

Yes... that would be fine.


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