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Chiller technician interview questions and how to answer them

A chiller interview is usually run by a service manager who has spent years on these machines, and they can tell within a few answers whether you've actually stood next to a centrifugal chiller or just read about one. Expect troubleshooting scenarios out loud, questions about how you document your work, and at least one question about what you do when a customer is losing cooling and wants it back now.

11 questions8 minute read

Part 1

1.Walk me through how you'd respond to a centrifugal chiller tripping on surge.

Why they ask

Surge is a classic centrifugal problem and the answer shows whether you think about the whole system or just the machine in front of you.

How to answer

  • Explain that surge means the compressor can't push against the lift it's being asked for, so flow reverses
  • Check condenser water temperature and flow first: a tripped tower fan, a closed valve or a fouled condenser raises head pressure
  • Look at load and guide vane position, since low load with high lift is the usual setup for surge
  • Pull the alarm history and trends from the controller before resetting anything
  • Only restart once you know the cause, and tell the customer what you found

2.The purge unit on a low-pressure chiller is running a lot more than usual. What does that tell you and what do you do?

Why they ask

Low-pressure machines run in a vacuum on the evaporator side, so purge activity is an early warning of a leak that lets air and moisture in.

How to answer

  • Excess purge run time means non-condensables are getting into the machine
  • Check purge logs and run counters to see when the change started
  • Leak check likely spots: gaskets, flare fittings, shaft seal on open-drive machines, relief devices
  • Pull an oil and refrigerant sample to check for moisture and acid
  • Document the finding and quote the repair before moisture damages the motor or oil

3.What's included in an annual inspection on a large water-cooled chiller?

Why they ask

Annual work is the bread and butter of chiller service, and a thorough answer shows you've done it, not just watched it.

How to answer

  • Pull condenser heads, brush tubes and inspect for scale, pitting and debris
  • Eddy current test tubes when the schedule or the customer calls for it
  • Oil analysis, filter change and a check of the oil heater and pump
  • Megger the motor, inspect starter or drive, tighten and check connections
  • Calibrate sensors, verify safeties trip at the right points, and write a clear report
4.How do you tell the difference between a chiller problem and a problem somewhere else in the plant?

Why they ask

Plenty of chiller calls turn out to be towers, pumps, valves or controls, and a tech who blames the chiller first wastes time and customer money.

How to answer

  • Start with approach temperatures on both barrels to see whether heat transfer is the issue
  • Check chilled and condenser water flow, delta T and pump status
  • Look at tower fans, basin levels and water treatment
  • Trend data in the building automation system to see what changed first
  • Give an example where the fix wasn't on the chiller
5.What's your lockout and tagout process before opening a chiller for repair?

Why they ask

These machines have large motors, medium or high voltage starters and pressurized water and refrigerant. Safety is a hiring filter, not a formality.

How to answer

  • Coordinate with the building engineer so the plant can run on another machine
  • Lock and tag the starter or drive, then verify zero energy with a meter
  • Isolate and drain water boxes, and confirm valves are closed and tagged
  • Recover or isolate refrigerant as needed before opening the system
  • Mention arc flash PPE when working in the starter or switchgear

Part 2

6.Which chiller makes and controllers have you worked on?

Why they ask

Each manufacturer has its own controller logic, service tools and quirks, and the answer tells them how much training you'll need.

How to answer

  • Name the manufacturers and machine types honestly: centrifugal, screw, scroll, absorption
  • Say which you've done teardowns or major repairs on versus routine service
  • Mention service software or controller interfaces you can connect to
  • Say what you'd want to learn first on their equipment
7.How do you handle refrigerant recovery and record keeping on a machine with a large charge?

Why they ask

Chillers hold big charges and leak rules are strict. They want someone who won't create a compliance problem.

How to answer

  • Use recovery equipment and cylinders rated for the refrigerant, and watch cylinder fill limits
  • On low-pressure machines, know how to use water or heat to speed recovery safely
  • Log amounts added and removed on every visit
  • Know that leak rate rules and repair deadlines exist, and follow the company's tracking process
  • Mention checking the rules that apply to the site rather than guessing
8.What would you do if an oil analysis came back showing high moisture and acid?

Why they ask

It tests whether you understand what lab reports mean for the machine's long-term health.

How to answer

  • Treat it as a sign of a leak or tube failure letting moisture in
  • Check for a leaking tube, especially on the evaporator, and leak test the machine
  • Change oil and filter drier, and consider an acid cleanup
  • Resample after repair to confirm it's clean
  • Explain the risk to the motor windings to the customer in plain terms
9.Tell me about a time you had to explain a big repair quote to a facility manager.

Why they ask

Chiller repairs are expensive, and techs are often the first person to tell a customer bad news.

How to answer

  • Set up the situation: the machine, the finding, what was at stake
  • Explain how you showed the evidence, such as photos, test results or trend data
  • Describe the options you gave, including the risk of waiting
  • Say how it ended and what you'd do the same way next time
10.A hospital calls at night because both chillers are down. What do you do in the first hour?

Why they ask

Emergency calls at critical sites are part of the job, and they want to hear priorities, not panic.

How to answer

  • Get alarm details on the phone so you arrive with the right tools and parts in mind
  • On site, check for a shared cause such as power, controls, condenser water or chilled water flow
  • Get one machine back first rather than splitting time between both
  • Keep the facility contact updated on what you know and what you're doing next
  • Call your lead or the factory support line early if it's beyond you

Part 3

11.How do you keep your skills current on newer equipment like magnetic-bearing compressors and variable speed drives?

Why they ask

Chiller technology keeps changing, and they want someone who will keep learning after the factory course.

How to answer

  • Name specific training you've taken or plan to take, such as manufacturer courses
  • Explain what's different about oil-free magnetic-bearing machines
  • Mention drive basics: harmonics, cooling, fault codes
  • Say how you learn on the job, such as working next to a senior tech on first startups

Questions to ask them

Ask at least two. It shows you're picking them too.

  • What mix of machines and manufacturers is on the service agreements I'd cover?
  • How does factory training work here, and how soon would I get to a manufacturer's school?
  • What does on-call look like in summer, and how are emergency calls split across the team?
  • Do techs run eddy current testing and oil sampling in house, or is that subcontracted?
  • How do you pair new chiller techs with senior ones during their first teardowns?

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