HVAC Service Technician Interview Questions
& Model Answers, 2026

Read together, those two numbers point to an undercharge or a liquid-line restriction starving the metering device. The distinguishing check is a temperature drop across the filter drier or a frost line at a restriction, plus verifying airflow first so you are not chasing a refrigerant symptom caused by a dirty coil or blocked filter. A technician who quotes only one of the two values, or who adds refrigerant before verifying airflow, is guessing.

Check the run capacitor first since it is the most common and cheapest failure, measuring capacitance rather than assuming from appearance, then the contactor for pitted or welded contacts, incoming voltage under load for a dropped leg or low supply, and the start components if fitted. Then measure winding resistance and check for a grounded or shorted winding before condemning the compressor. Also consider a mechanically locked compressor from liquid slugging.

Start where leaks actually occur — service valves and schrader cores, brazed joints, the coil hairpins and return bends, and anywhere the line rubs a bracket. Use an electronic detector methodically from the bottom up in still air, back it up with bubble solution or ultraviolet dye, and if the system is empty, pressurise with dry nitrogen and listen. Say that you always find and report the leak rather than topping up and leaving, which is both bad practice and a compliance problem.

The reversing valve swaps the roles of the indoor and outdoor coils, driven by a solenoid that is energised in one mode. Defrost is initiated by time and temperature or by demand, and terminated by coil temperature. When a heat pump ices, check the defrost board and sensor, whether the reversing valve is fully shifting — a valve stuck mid-position shows as an abnormally warm suction line and poor capacity — the outdoor fan operation during defrost, and the charge. Auxiliary heat locking on is a symptom, not the fault.

Airflow first: filter, blower wheel condition, evaporator coil, closed registers and duct restriction, because the limit is doing its job if the furnace cannot move enough air. Then the blower speed tap, the limit switch itself, gas pressure and firing rate against the rating plate, and the heat exchanger condition. A combustion analysis and a heat-exchanger inspection are how you decide whether this is a repair or a red-tag.

Venting refrigerant is prohibited, so it must be recovered into a certified recovery cylinder with a recovery machine before any repair that opens the system, evacuated to the required level for the equipment size, and the cylinder must not be overfilled. Leaks above the applicable threshold on larger systems trigger repair and verification requirements. Say that you hold the EPA Section 608 certification for the equipment you work on and that you record the charge added and recovered on the ticket.

Everybody has one: a compressor condemned that was a capacitor, a leak chased that was a drain issue, an airflow problem treated as a charge problem. The good answer describes what misled you, how the callback or the second technician revealed it, that you told the customer honestly and adjusted the bill, and the diagnostic step you added. Refusing to admit an error is the answer that loses the job.

Present the facts before the recommendation: what has failed, what the repair costs, the age and condition of the rest of the system, and what a replacement would cost, then let them decide. Do not exaggerate the failure to sell equipment, and do not talk them into a repair you expect to fail. Service managers listen closely here, because technicians who oversell generate revenue this quarter and refunds next.

Usually a repeat visit or a missed appointment window. The strong version acknowledges the problem without blaming the office in front of them, gets to the diagnosis quickly to show progress, gives an honest timeline, and follows up with the office so the underlying cause — dispatch, parts, a previous misdiagnosis — actually gets fixed.

Real prioritisation: no-cool calls with vulnerable occupants or commercial food loss first, honest updates to dispatch about how long you actually are, not cutting a diagnosis short to make a number, and carrying the parts that fail most so a second trip is not needed. Mention that you tell dispatch when you cannot make a window rather than letting a customer wait all day.

Use the published anchor and then specify. The BLS OEWS May 2025 national median for heating, air conditioning and refrigeration mechanics and installers is $61,010 a year ($29.33/hr), with the top 10% above $95,210; that series blends installers and commercial refrigeration mechanics with residential service, so state your own mix. A diagnostic technician with a strong first-visit fix rate and commercial capability should be arguing for the upper part of the band.

Most service pay is a base plus a percentage of billed labour, parts, maintenance agreements or equipment leads. Confirm the percentage, what it is calculated on, whether it is paid on collected revenue, whether callbacks are charged back to you, how it works when you diagnose and someone else installs, and whether maintenance-agreement sales carry their own spiff. A commission structure that pays on equipment leads can quietly push a technician toward overselling.

The on-call rotation and how call-outs are paid, a stocked take-home van, a tool allowance for gauges, a leak detector and a combustion analyser, employer-paid manufacturer and EPA training, paid drive time, and how hours are protected in the shoulder seasons. Also ask whether diagnostic time is billed and paid properly, because a shop that will not pay for careful diagnosis is a shop with a callback problem.