Thermostat Wiring Colors Code | HVAC Control Wire Details Jul 04, 2008Thermostat Wiring Colors Code - High Performance HVAC Thermostat Terminal Designations. Turn the power off before proceeding! Always follow safety instructions especially with electricity. This should be done at the circuit breaker for both the condenser and the air handler/furnace.How to Wire a Thermostat · Single Transformer Legacy Brands | Nortek Global HVAC Legacy Brands. Nortek Global HVAC has a long history of creating quality heating and air conditioning products in the residential, manufactured housing and light commercial markets. Over the years, we have commanded a strong portfolio of top tier brands, some of which are no longer in production.