wiring hvac 24 ac transformer color code wiring

There was no 'C' wire in these installations because the thermostat simply functioned as a very low-voltage on-off switch that had so little going on that it didn't need its own power source.īut when going to a new smart thermostat like the Nest, that device needs more power for its display and other features. Our photo shows a low voltage24VAC transformer mounted next to the line voltage (120VAC) electrical power switch for a heating boiler.Ī 'missing C-Wire' or 'no Common Wire' at the thermostat is a common problem I've run into on some older homes that had just two wires (usually red and white) running from a heating furnace or boiler to the thermostat.

Connecting the C-Wire and How to Add one If It's Missing We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. Sometimes the transformer is inside the HVAC equipment itself. The C-wire or 'COMMON' wire in heating and cooling or heat pump applications is a source of 24-volt AC power needed by certain controls and also needed by some, but not all, room thermostats.Ģ4VAC is provided to the C-wire right from a 24-volt AC transformer usually found mounted in or near the heating furnace, boiler, or air conditioner's air-handler. This article describes the function of the C wire in heating and cooling equipment and gives four methods for adding a C wire if your thermostat needs one. We have no relationship with advertisers, products, or services discussed at this website. InspectAPedia tolerates no conflicts of interest.

Wiring hvac 24 ac transformer color code wiring