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Compressor Technician interview questions and how to answer them

A compressor tech interview is really a troubleshooting test wearing a collared shirt. The service manager wants to hear how you think when a unit trips, whether you'll work safely when nobody's watching, and whether a customer will trust you in their plant. Expect a mix of technical questions, a walk through a failure you've fixed, and some blunt talk about on-call and travel.

11 questions8 minute read

Part 1

1.A rotary screw compressor keeps shutting down on high discharge temperature. Walk me through how you'd find the cause.

Why they ask

This is the most common fault call on screw units, and it tells them straight away whether you troubleshoot in a logical order or start throwing parts at it.

How to answer

  • Start with the easy checks: oil level, the condition of the cooler and whether the room is too hot or starved for ventilation
  • Check the thermal valve and oil filter, since a stuck thermal valve or clogged filter will cut oil flow to the air end
  • Confirm the temperature sensor reads true against an infrared thermometer before trusting the controller
  • Look at the oil itself and the service history for signs of varnish or the wrong fluid
  • Explain that you'd write up what you found so the next tech doesn't start from scratch

2.Tell me about a time you fixed a compressor that another tech couldn't.

Why they ask

They want a real story with a real machine in it, because it shows how you think under pressure and if you're honest about what you didn't know.

How to answer

  • Name the type of unit and the setting, such as a reciprocating unit in a body shop or a screw unit in a food plant
  • Describe what had already been tried and why it didn't hold
  • Walk through the test or reading that pointed you to the real cause
  • Say what you changed and how you confirmed the fix held over the following visits

3.How do you do a lockout before working on a compressor?

Why they ask

Stored air pressure and automatic restarts injure people, so they need to hear that you isolate every energy source, not just the breaker.

How to answer

  • Tell the customer's contact before you start and follow their lockout procedure as well as your own
  • Shut down the unit, open and lock the disconnect, and apply your own lock and tag
  • Close and lock the isolation valve and bleed down the receiver and lines until gauges read zero
  • Verify with a meter and a restart attempt that the unit is truly dead before you open anything
4.What's the difference between servicing a reciprocating compressor and a rotary screw?

Why they ask

Plenty of shops service both, and your answer shows whether you've actually had your hands on each or only read about them.

How to answer

  • Reciprocating units have valves, rings, packing and crankcase oil, and you'll inspect or replace valves on a set interval
  • Screw units are oil-flooded, so separator elements, oil filters, oil analysis and thermal valves carry more of the PM
  • Recips are more tolerant of intermittent duty; screws prefer long run times and suffer if they short cycle
  • Mention a specific repair you've done on each type
5.A customer says their plant air pressure drops every afternoon. How do you figure out whether it's the compressor or the system?

Why they ask

A lot of so-called compressor problems are leaks, undersized piping or new demand, and a good tech saves the customer money by finding that.

How to answer

  • Check the compressor's own output, load and unload behavior and controller history first
  • Compare pressure at the compressor discharge with pressure at the far end of the plant to spot piping or dryer drop
  • Look at clogged filters and dryer pressure drop before blaming the compressor
  • Run an ultrasonic leak survey and ask what equipment was added recently
  • Recommend a fix in writing, whether that's repair, a leak program or a second unit

Part 2

6.How comfortable are you troubleshooting motor controls and VFDs?

Why they ask

Electrical faults are where most mechanically strong techs get stuck, and it's the skill that's hardest for a shop to teach.

How to answer

  • Be honest about your level, from basic starter and contactor work up to drive faults
  • Describe reading a ladder or wiring diagram and tracing a control circuit with a meter
  • Give one example, such as a failed contactor, a bad pressure transducer or a drive tripping on overcurrent
  • Mention where you'd stop and call a licensed electrician if the work goes beyond your scope
7.What do you look for in an oil analysis report on a screw compressor?

Why they ask

Predictive work is where service contracts earn their keep, and they want techs who can read a report and act on it.

How to answer

  • Wear metals that point to bearing or rotor wear
  • Water content, which hints at a drain or temperature problem
  • Viscosity and oxidation, which say whether the oil is breaking down early
  • Trend over several samples rather than reacting to one reading
  • What you'd recommend to the customer based on each finding
8.How do you handle a plant manager who's angry because production is down?

Why they ask

You're the face of the company on a bad day, and a tech who argues or disappears loses the account.

How to answer

  • Acknowledge the pressure they're under and tell them what you're checking first
  • Give short, honest updates instead of guessing at a finish time
  • Offer options like a rental unit or a temporary bypass if the repair will take a while
  • Follow up with a clear written report once it's running
9.Walk me through a typical preventive maintenance visit on a screw unit.

Why they ask

Most of the job is PMs, and a sloppy one causes the breakdown calls later.

How to answer

  • Review the service history and controller fault log before starting
  • Lock out, then change filters, separator and oil on the right interval and check belts or coupling
  • Clean coolers, check drains, test safety shutdowns and pull an oil sample
  • Take vibration and temperature readings for trending
  • Write the report with findings and any recommended repair
10.How do you feel about on-call, overtime and travel?

Why they ask

Every compressor shop has to cover nights and weekends, and people who aren't honest about this quit fast.

How to answer

  • Say plainly what you can commit to and ask how the rotation actually works
  • Mention a past role where you covered call and how you managed it
  • Ask about response time expectations and how call pay is handled

Part 3

11.Why do you want to work on compressors instead of general maintenance?

Why they ask

They're checking whether you'll stick around long enough to be worth the factory training.

How to answer

  • Point to something specific you like, such as troubleshooting rotating equipment or working independently on a route
  • Connect it to a job or task you've already done
  • Show interest in the equipment lines this company services

Questions to ask them

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

  • Which compressor lines and controllers do your techs service most, and what factory training do new techs get?
  • How long do new techs work in the shop or ride along before they get their own route?
  • How does the on-call rotation work, and how many calls does a tech usually get on a call week?
  • What does a good service report look like here, and who reads them?
  • What's the most common reason a new tech hasn't worked out on this team?

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