Heat transfer, sensible vs. latent heat, psychrometrics, pressure, airflow, the refrigeration cycle, and the terminology every later module in this program assumes you already have.
Most HVAC training jumps straight to equipment selection and code tables. This module deliberately starts one level up: what heat actually is and how it moves, why sensible and latent loads are two different numbers with two different jobs, how to read moist air on a psychrometric chart, why HVAC measures pressure in inches of water instead of psi, and what the four processes of the refrigeration cycle actually do to the refrigerant at each stage.
By the end of this module you should be able to explain, from first principles, why two rooms at the identical dry-bulb temperature can feel completely different, and why a unit sized only against a sensible BTU/h target can still leave a humid space feeling clammy — a question Module 4's load-calculation content answers in full worked-example detail.