Air Conditioning and Refrigeration Guide: common sense tips on maintaining, troubleshooting and repairing a variety of air conditioning and refrigeration equipment. Also, service tips and training guide.
BTU Calculator: Provided by calculator.net can help you estimate how much BTU will be needed to cool or heat an area.
FreeCalc: applications for everyday mathematics, engineering, economics, and scientific calculations.
Virginia Mechanical Code 2018: online resource from ICC.
Refrigeration Service Engineers Society (RSES): training resource for HVAC professionals
SolRus: General resources for HVAC professionals