AK HVAC common mistakes
AK HVAC · Understand the traps and how to avoid them.
Calculating sensible and latent heat separately but then reporting total heat as if it were sensible only, or mixing the two in a single formula (e.g., using the total heat equation when only a dry-bulb temperature change is given).
Candidates memorize both the sensible heat factor (1.08 x CFM x ΔT) and the total heat factor (4.5 x CFM x Δh) but forget that the 1.08 constant applies only when there is no moisture change, and the 4.5 constant requires an enthalpy difference, not a temperature difference.
What to do instead
Before plugging numbers, write down which quantities are known and whether a moisture change is present. If only dry-bulb changes, use the sensible equation; if wet-bulb or enthalpy data is given, use the total heat equation and split with the sensible heat ratio. Practice five mixed problems until the constant selection is automatic.
Treating refrigerant saturation pressure and temperature as independent variables, or reading a P-T chart at the wrong point (e.g., using suction line temperature instead of saturation temperature to find superheat).
Superheat and subcooling require subtracting a saturation temperature (from pressure) from a measured line temperature. Candidates often confuse the two temperatures or use the wrong pressure tap, especially on systems with a receiver or a thermostatic expansion valve.
What to do instead
Drill the definitions: superheat = suction line temp minus saturation temp at suction pressure; subcooling = saturation temp at liquid pressure minus liquid line temp. Always state the pressure tap location before computing. Work through one example on a system with a receiver and one without.
Sizing ductwork or selecting a blower using velocity alone without checking static pressure, or converting between round and rectangular equivalents by matching area only rather than equivalent friction.
Candidates learn the friction chart and the equal-area shortcut and then apply the shortcut when the question is testing equal friction or equal velocity. The three equivalence methods give different answers.
What to do instead
Identify which equivalence the question asks for (equal area, equal friction, or equal velocity) before converting. On the exam, write the method name next to the calculation. Practice converting one round duct to rectangular using all three methods and compare the results.
Applying the general (lower-48) combustion air, venting, or clearance rules to an Alaska installation without checking for the cold-climate and seismic provisions, or ignoring that outdoor design temperatures below the equipment rating change the required configuration.
Most study material is written for temperate climates. Alaska installations involve extreme design temperatures, snow loads, permafrost, and seismic zones that alter venting, combustion air, and equipment placement requirements.
What to do instead
Build a one-page Alaska addendum covering cold-climate venting, combustion air in tight construction, freeze protection, and seismic restraint, and review it before every practice set. When a question mentions Alaska or a design temperature, flag it and check the addendum first.
Confusing the roles of the thermostat, the control transformer, and the contactor when tracing a low-voltage circuit, and misidentifying which terminal (R, W, Y, G, C) carries which signal.
Candidates memorize terminal letters without understanding the circuit path, so they cannot diagnose an open safety, a failed transformer, or a miswired fan control under exam conditions.
What to do instead
Draw the low-voltage circuit from transformer through thermostat, safety switches, and contactor coil, labeling each terminal and its function. Redraw it from memory daily until you can trace a call for heat and a call for cooling without looking.
Skipping the lockout/tagout and refrigerant recovery steps in scenario questions, or answering the 'what should the tech do first' question with the repair step instead of the safety or isolation step.
Candidates focus on the technical fix and treat safety procedures as boilerplate, but exam scenarios frequently test the order of operations, and the first correct action is usually isolation or verification, not repair.
What to do instead
For every scenario question, ask 'what must be true before I touch anything?' and eliminate answers that skip isolation, verification, or recovery. Memorize the sequence: identify, isolate, verify, then work.
Mixing up the psychrometric properties (dry-bulb, wet-bulb, dew point, relative humidity, enthalpy, specific volume) and reading the chart along the wrong line.
The chart has six families of lines and candidates learn them by position rather than by definition, so they follow a constant-humidity line when the question asks for a constant-enthalpy process.
What to do instead
Label a blank psychrometric chart from memory weekly, naming each line family and its units. For process questions, identify the two fixed properties first, then read the third along the correct line.
Miscalculating Alaska-specific load factors such as infiltration driven by wind and stack effect, or ignoring the effect of a large indoor-outdoor temperature difference on vapor drive and insulation placement.
Candidates apply generic load assumptions and standard insulation placement rules that assume warm-humid climates, but in Alaska the vapor drive is often from inside to outside in winter, changing where the vapor barrier belongs.
What to do instead
Study cold-climate building science separately: stack effect, wind washing, and vapor barrier placement in heating-dominated climates. On load questions, state the direction of vapor drive before selecting an answer.
Answering licensing and business-law questions from general contracting intuition rather than Alaska-specific statutes, such as assuming a statewide license covers all municipalities or misstating bonding and lien requirements.
The business and law portion is state-specific and candidates often study it last, relying on general knowledge that does not match Alaska requirements for endorsement, bonding, lien deadlines, or contractor registration.
What to do instead
Create a dedicated Alaska business-and-law outline covering licensing tiers, bonding, lien notice and deadline rules, and local permit authority, and review it in short daily sessions rather than cramming at the end.
Guessing at tool selection or code compliance for a task (e.g., using a manifold gauge set to leak-test with nitrogen, or citing a clearance without the code section) instead of naming the correct instrument and the governing requirement.
Candidates know the tools exist but not their limits, and they treat code questions as recall of a number rather than recall of a requirement with conditions and exceptions.
What to do instead
Pair each common task with its correct instrument and the code requirement that governs it, and note the conditions or exceptions attached to each number. If you cannot state the condition, mark the item for review rather than guessing.