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HVAC School - For Techs, By Techs

May 14, 2020

Bryan and Kaleb cover the basics of low-voltage electrical applications. They focus on the practical stuff, not just the theory that confuses techs.

Many techs have a hard time with low-voltage electrical concepts and components because it's not easy to visualize what happens; we only see wiring diagrams, not metaphors that help us understand what's going on.

The low-voltage control circuit starts with the transformer. The transformer has a primary side (where the high voltage comes in) and a secondary side (where the lower voltage comes out). The secondary is only connected to the primary via electromagnetism; it helps to think of the secondary as an independent electrical circuit.

Color coding is a simple concept, but it has changed over the years and can confuse techs. You can only truly understand the wires by doing a complete visual inspection and tracing the wiring. (Though generally, blue will be common/C, and red will be hot/R.) We also typically use yellow for Y1, but Y is a confusing concept. Y ISN'T the compressor or cooling! Y pulls in the contactor coil; it is really the high-stage contactor. Y2 is a higher staging, and Y1 is a lower staging. On heat pumps, the white wire is usually for heating, and the orange wire is usually for the reversing valve. G is for the indoor fan and often has a green wire.

Kaleb and Bryan also discuss:

  • Tapping transformers
  • W and O calls on heat pumps
  • G calls
  • DH on 24v controls
  • Communicating controls
  • Float switch configurations and issues
  • Breaking Y or R with the float switch
  • Wire routing: air handler and condenser
  • Preventing conductor corrosion
  • NASA or lineman splice
  • Stranded shielded wire vs. solid wire

Learn more about Refrigeration Technologies HERE.

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