Linked Questions

4 votes
6 answers
6k views

Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...
1 vote
0 answers
108 views

How do I go about wiring 3 Nests to a boiler with no C wire

I’ve seen a version of this question in a few places but nothing really fits. I have a boiler and hot water baseboards. It’s a three zone system and I installed 3 Nests but there is not C wire and no ...
1 vote
8 answers
24k views

I am installing a Honeywell RTH6580WF with a TACO SR504

The current installation does not have a C wire. So I have run an extra wire and am now confused as to where to connect it. There is a 24VAC connection and a common connection. Comments say that ...
1 vote
3 answers
42k views

How do I connect the common wire in a Carrier air handler?

I am trying to install a new wifi thermostat in my home and need to locate the common terminal for my air handler. I have a Carrier model FB4CNF030. It's a new construction home and I have the blue ...
0 votes
1 answer
2k views

Add C wire to very old gas furnace

There is a very old gas furnace in our attic. It has a two-wire transformer and no obvious terminals to expand. I need to run a C wire to my nest thermostat, which I'm planning to do via their nest ...
-1 votes
1 answer
81 views

Adding a c wire for a thermostat

Trying to add a C wire for a new Nest thermostat. Currently only have a Red and White wire. There are no other terminals available for the C wire on the furnace transformer. Red go to one end of the ...
1 vote
2 answers
479 views

Where to connect the C Wire? See pictures and diagram [duplicate]

I have Rheem RBHC-14A00NFA AC unit. I am trying to install nest thermostat but don’t know where to connect the C wire. I am attaching the picture of the wires and the diagram. Please help! Thanks
0 votes
0 answers
140 views

HVAC adding C wire to older system w/ wire nuts

I have an older system, separate AC and gas heat. Trying to add a C wire. All existing wires are connected outside the air handler with wire nuts. I've unwrapped an unused blue in the lower right of ...
3 votes
1 answer
447 views

Can't find HVAC C terminal

Could any of these be the c terminal on my hvac unit? There's already a c wire there, just can't figure out where to connect it.
0 votes
1 answer
820 views

How can I implement an unused wire as a C wire for my thermostat? [duplicate]

I have a boiler system that uses 2 wires to the thermostat. I am going to buy a new thermostat that needs a C wire. There is a spare wire not being used and it is not hooked up to anything. How can I ...
2 votes
2 answers
14k views

Adding a C Wire using a 24V AC Transformer to a 2 Wire Heating System for Nest

Continuation from Can I use any of my existing oil control terminals (TTFFAA) for a C wire? EDIT: Wanted to finally say this is SOLVED with help from @JPhi1618 (see conversation below). If you have a ...
1 vote
0 answers
2k views

Problem connection C wire into Lennox Furnace

I would like to connect my new Honeywell WiFi thermostat (RTH6580WF1001) to a Lennox Elite dual Heater and Cooler system. I don’t have a C wire in my old thermostat. I have read online that I can ...
0 votes
1 answer
2k views

Can I directly add a Common wire to this point on a 24VAC transformer, or will load be too high? (70mA)

Referencing This excellent answer I have a two wire furnace controller, 24VAC, no common. I measured the current draw of the relay (when the thermostat wires are shorted), it draws 0.2A Wish to add an ...
1 vote
1 answer
1k views

How to connect a new C wire

I have a 2 zone, single stage, heat only system with 2 wires running to each thermostat. I'm looking to install 2 Ecobee's; I have a second Honeywell AT72D1683 that I can install if needed and have ...
2 votes
2 answers
11k views

How do I connect a WiFi thermostat to my furnace's primary control?

I would like to install a Honeywell WiFi controlled thermostat to connect to a Honeywell R7184U primary control. My question concerns the "C" wire. The R7184 has the terminals labeled 1, 2, 3 and 4 ...

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