HVAC Cheat Sheet 2026

The 30 highest-yield HVAC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. In commercial HVAC design, what is the purpose of a smoke control system? → To manage airflow during a fire to protect egress paths and aid firefighting
2. What is the maximum fill level (by weight) for a recovery cylinder? → 80%
3. What is the purpose of vacuuming a mini-split system before charging? → Both B and C — remove air/moisture and verify leak-free
4. What troubleshooting method uses the process of elimination by testing components from 'most likely to least likely'? → The probable-cause method
5. What does a 'chilled water coil' use instead of direct refrigerant expansion? → Cold water (typically 44-46°F) circulated from a central chiller
6. What is the purpose of a disconnect switch near an outdoor HVAC unit? → To provide a local means of de-energizing the unit for safe service work
7. Which type of air handler configuration has the blower located downstream of the coil? → Draw-through
8. Commercial HVAC maintenance contracts differ from residential service agreements primarily in that commercial contracts typically include: → More frequent scheduled maintenance visits and detailed performance reporting
9. Which refrigerant has been the standard for new residential split systems since R-22 was phased out? → R-410A
10. A technician finds oil staining around a brazed refrigerant joint on a rooftop unit. What should be done before adding refrigerant? → Repair the leak, pressure-test, evacuate, then recharge
11. In a BAS, what does a PID controller stand for? → Proportional-Integral-Derivative
12. What is the primary purpose of an oil separator used during refrigerant recovery? → To separate compressor oil from refrigerant before it enters the recovery cylinder
13. What is the function of a 'passive' or 'system-dependent' recovery device? → It uses the system's own compressor to push refrigerant into the recovery cylinder
14. A technician recovers refrigerant into a cylinder that already contains a different refrigerant. What must happen to this cylinder? → It must be labeled as mixed/contaminated and sent to a refrigerant reclaimer
15. Which BAS sequence of operation step typically follows the morning warm-up mode? → Occupied mode
16. In a BAS, what is the purpose of the 'priority array' in BACnet commandable objects? → Manage multiple competing commands to an output by assigning priority levels 1-16
17. Which code or standard establishes minimum efficiency requirements for residential central air conditioners in the United States? → DOE minimum efficiency standards (SEER ratings)
18. A heat recovery ventilator (HRV) is used in residential buildings primarily to: → Exchange stale indoor air for fresh outdoor air while recovering heat energy
19. Which recovery method is fastest for recovering large amounts of liquid refrigerant? → Liquid recovery first, then vapor
20. What does 'ASHRAE 90.1' establish that BAS designers must follow? → Energy efficiency standards including HVAC controls requirements for commercial buildings
21. What is the most common cause of a clogged condensate drain line? → Algae and biological growth in the drain line
22. What is the purpose of a Variable Air Volume (VAV) box in a BAS-controlled system? → To modulate airflow to individual zones to maintain zone temperature setpoints
23. Which commercial HVAC system component is responsible for distributing conditioned air to specific zones based on thermostat demand? → VAV terminal box
24. What type of coil is used in an air handler for the heating mode in a heat pump system? → The same evaporator coil, which acts as a condenser during heating mode
25. What does 'superheat' refer to in the context of an evaporator coil? → The temperature of refrigerant vapor above its saturation temperature
26. What is the function of a 'hard-start kit' (potential relay and start capacitor) on an air handler? → It is not used on air handlers — only on compressors
27. What is the typical fin spacing (fins per inch) for a residential evaporator coil? → 8-14 fins per inch
28. What is the primary advantage of a two-stage or variable-speed gas furnace? → Improved comfort and efficiency by operating at lower capacity most of the time
29. Duct leakage testing is required by energy codes primarily in: → New residential construction to verify duct system integrity
30. What unit is used to measure the cooling capacity of HVAC equipment in the US? → BTU/hr or tons