HVAC and Refrigeration Trade Competency
What the exam tests
The HVAC and refrigeration portion of the Ohio contractor exam tests whether you can apply trade theory to field decisions: building heat gain/loss, equipment and duct selection, refrigerant-cycle diagnosis, combustion and venting, controls, and safe recovery/evacuation. Questions often give a field scenario and ask for the next diagnostic step or the calculation that supports a recommendation.
Core rules and concepts
- Sensible heat in air is approximated by Qs = 1.08 × cfm × ΔT; total heat adds latent load, so do not use the sensible formula for a wet coil.
- The refrigeration cycle moves heat from evaporator to condenser. Superheat is measured at the evaporator outlet; subcooling at the condenser outlet. Target values come from the equipment manufacturer, not a universal number.
- Airflow is a prerequisite for charging. A dirty filter, restricted coil, or wrong blower speed can mimic a refrigerant problem.
- Duct sizing uses available static pressure and friction loss; manual dampers and balancing are part of commissioning.
- Refrigerant handling requires recovery, nitrogen purge while brazing, and evacuation measured in microns. Never use refrigerant to purge or leak-test.
- Combustion appliances need adequate combustion air and proper venting; check draft and CO after service.
Worked example
A 400-cfm air handler has 75°F return air and 55°F supply air. Sensible capacity is 1.08 × 400 × (75−55) = 8,640 Btu/h. If the measured capacity is far below the equipment rating, first verify airflow and temperature measurement locations. The formula does not include latent capacity, so a wet coil can have a higher total capacity than the sensible result.
Traps
Charging by gauge pressure alone; assuming a 20°F ΔT is always correct; adjusting refrigerant before checking airflow; ignoring superheat/subcooling targets; and treating a vacuum decay test as optional.