HVAC Technician interview questions and sample answers

A hvac technician interview usually mixes two kinds of question: ones that test whether you know the job, and behavioral ones that ask for proof from your past. Below are 10 of the first with a short model answer, and 5 of the second with what the interviewer is really checking. Rewrite every answer in your own words and with your own numbers.

Job-specific questions

1. How do you diagnose a system that's not cooling?

I check refrigerant charge with gauges against the manufacturer's superheat and subcooling targets, check airflow at the coil, and check the capacitor and contactor in the outdoor unit before assuming a refrigerant leak.

2. What's your process for checking refrigerant charge on a TXV system?

I measure subcooling at the liquid line and compare it to the manufacturer's spec, usually 8-12 degrees, rather than relying on superheat, which applies to fixed orifice systems, not TXV metering devices.

3. How do you size a replacement system for a home?

I run a Manual J load calculation rather than matching existing tonnage, since older systems are often oversized. I factor in square footage, insulation, window count, and orientation before recommending equipment.

4. A customer's furnace short cycles. What's your troubleshooting order?

I check the flame sensor for corrosion first, then the air filter for restriction, then limit switch settings. A dirty flame sensor is the most common cause I find, so I clean it with fine sandpaper.

5. How do you verify proper airflow on a new install?

I measure static pressure with a manometer across the coil and filter, comparing readings to the blower's rated CFM table, targeting total external static under 0.5 inches on most residential systems.

6. What safety checks do you run before leaving a gas furnace job?

I test for carbon monoxide with a combustion analyzer, check flue draft, verify gas pressure at the manifold matches spec, usually 3.5 inches WC for natural gas, and inspect the heat exchanger for cracks.

7. How do you handle a refrigerant leak on an older R-22 system?

I locate the leak with an electronic sniffer or UV dye, then discuss replacement options since R-22 is phased out and expensive. Repairing and recharging an old system rarely pays off financially for the customer.

8. What's your approach to duct sealing on an efficiency job?

I use mastic sealant or foil tape rated UL 181, not standard duct tape, and I test results with a duct blaster where the job calls for verified leakage numbers.

9. How do you explain a repair versus replace decision to a customer?

I compare repair cost against remaining system life and efficiency. If repair exceeds 30 percent of replacement cost on an older unit, replacement usually pays off faster through energy savings.

10. Describe your commissioning checklist for a new AC install.

I verify refrigerant charge, check static pressure, confirm thermostat calibration, test the disconnect and breaker sizing, and record startup readings on the manufacturer's checklist for warranty documentation.

Behavioral questions

Answer these with STAR: the Situation in one sentence, the Task, the Action you took (most of the answer), the Result with a number.

11. Tell me about a result you are proud of.

What they are checking: A specific outcome with a number, and what you personally did to get it.

A result to build the answer around: Service and repair about 5 residential and commercial systems a day.

12. Describe a time you improved how something was done.

What they are checking: That you notice waste and fix it without being told, then measure the difference.

A result to build the answer around: Installed 180 heat pumps and furnaces with zero failed inspections.

13. Tell me about a time you had to deliver under pressure.

What they are checking: How you prioritise, communicate early and still finish to standard.

A result to build the answer around: Grew maintenance contracts on my route by 30% with clear inspection reports.

14. Give an example of working with a difficult colleague or customer.

What they are checking: Calm, the other person's view stated fairly, and a result that helped both sides.

A result to build the answer around: Diagnosed intermittent faults others missed, cutting repeat visits by 25%.

15. What is something you learned from a mistake?

What they are checking: Ownership without excuses, and the habit you changed so it did not happen again.

A result to build the answer around: Trained 3 apprentices to work independently within 6 months.

Before the interview

Interviewers read your resume just before they walk in, and most questions come from it. Every bullet on it should be one you can expand into a two-minute STAR story. Check that it matches the posting with the free ATS Match Score, and look at the hvac technician resume keywords the ad is likely to use.

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