Check your local community college, which may have a short-term program in HVAC. For example, North Seattle Community College offers a 1.5-year certificate program, where students complete courses such as Introduction to Electricity and Electronics, Essentials of HVAC, plus Cooling and Heating Service.
Search introductory HVAC-related books in the trade or technical sections of online booksellers such as Amazon, Barnes & Noble or Book Closeouts, such as "Fundamentals of HVAC/R" by Carter Stanfield, "No Ducks in the Attic: & Other Basics of HVAC Installation" by RJ Schuster, or "HVAC Fundamentals, Heating Systems, Furnaces and Boilers" by James E. Brumbaugh.
Enroll as an apprentice, where the training organization plots out a specialized series of coursework tailored to your interest, such as Penn Foster's program, where coursework includes Reading Piping Prints, Servicing Gas Appliances, Basic Air Conditioning, Predictive Maintenance and Insulation for Piping and Ducting.
Sign up for a webinar, which is a live or pre-recorded seminar held over the Internet. A variety of companies and organizations present HVAC webinars, including the Sheet Metal and Air Conditioning Contractors' National Association, with topics such as "HVAC Understanding the Basics," "HVAC System Control" and "HVAC Operation."
Join an HVAC industry association, national organizations created to promote the HVAC industry. Most groups, such as the Air Conditioning Contractors of America, offer training for members (though non-members may often attend training as well for an additional charge), with courses in HVAC essentials, online training plus national conventions such as the "Indoor Air Expo."