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Leak Detection & Repair — EPA 608 Practice Questions

31 questions · 25% of the Type II — High Pressure exam

Worked questions

1. A technician is sweeping an electronic leak detector along the brazed joints of an R-134a rack looking for a small leak. How should the probe be handled to give the best chance of finding it?

  • AHeld about a foot back from the joints and swept quickly along the line, so the sensor does not saturate on background vapor and false-trigger

    Distance and speed both work against the sweep. A foot of separation lets the plume disperse below what the sensor can detect, and a fast pass gives it no time to respond, so a small leak is walked right past.

  • BPassed a few inches above each joint and moved slowly, since refrigerant vapor is lighter than air and drifts upward

    This treats refrigerant as a light gas. Common refrigerant vapors are heavier than air and sink away from the joint, so a probe held above it samples clean air while the leak is escaping downward.

  • Moved slowly along the underside of each joint about an inch away, since these refrigerant vapors are heavier than air and settle downward
  • DParked in one spot in the machine room for several minutes to sample the whole space, then moved to the far wall

    A stationary probe reads general room background instead of a specific fitting. It may confirm that refrigerant is escaping somewhere in the room, but it will never say which joint needs the repair.

Why C is correct

Refrigerant vapor is denser than air and falls away from the leak, so the sensor has the best chance of picking it up just below and very close to the joint. Slow movement gives the detector time to respond, which is what catches small leaks.

What this question is testing

This tests hands-on leak detection technique rather than definitions, specifically the physical behavior of refrigerant vapor around a leak and how probe speed, probe distance, and probe position affect whether a small leak is caught. It rewards the field habits that separate a productive leak search from a wasted afternoon.

On the job

On a rack with a hundred brazed joints, technique is the difference between a two-hour leak search and a callback next week. Techs shut off ceiling fans and condenser fans where they can, let the room settle, then work bottom to top and slow. A detector that is too sensitive alarms constantly in a room with background refrigerant, so most techs step outside to zero the unit, then come back in. Confirming every detector hit with bubbles before firing up a torch is standard discipline.

Memory technique

Refrigerant falls, so hunt low and go slow.

Exam tip

Remember that refrigerant vapor sinks. Any answer that has you scanning above a joint or hurrying the probe along is wrong.

Where to look it up

Electronic detector practice: probe below the joint, roughly one inch away, moving about one to two inches per second.

2. A technician sweeps an ultrasonic leak detector along the piping of a pressurized system. What is that instrument actually responding to?

  • AThe temperature drop created where refrigerant expands as it escapes

    Temperature drop at a small leak is far too slight and too localized to be the operating principle, and no field ultrasonic detector measures temperature.

  • The high-frequency sound produced by gas rushing through a small opening
  • CChemical traces the escaping refrigerant leaves behind on nearby metal surfaces

    Refrigerant leaves oil residue at some leak sites, but that is something a technician looks for by eye. No handheld instrument analyzes surface chemistry.

  • DThe change in electrical resistance caused by refrigerant vapor at the probe tip

    Resistance and ionization sensing describe electronic refrigerant detectors, which respond to the refrigerant itself and are blind to nitrogen.

Why B is correct

The instrument is a microphone tuned to ultrasonic frequencies. Turbulence at a leak orifice generates that sound regardless of what gas is passing through, which is why the same tool finds a nitrogen leak, a refrigerant leak, or a compressed air leak with equal ease.

What this question is testing

The candidate must identify the physical principle behind an ultrasonic detector and infer from that principle where the tool fits, particularly its ability to work with nitrogen.

On the job

The ultrasonic detector earns its keep during nitrogen pressure testing, when an electronic refrigerant detector is useless, and on large systems where you can stand back and sweep quickly. It is also the tool for large leaks that saturate an electronic detector and leave it alarming everywhere. The limitation is a noisy plant room, where compressors, fans and steam traps generate ultrasound of their own, so techs often shut equipment down or work during off hours.

Memory technique

Ultrasonic hears the hiss. If gas is moving, it does not care which gas.

Exam tip

Ask what each detector senses. Refrigerant detectors sense refrigerant, ultrasonic detectors sense sound, and that difference decides which one works during a nitrogen test.

Where to look it up

Leak detection methods and verification testing are addressed under 40 CFR Part 82, Subpart F. Ultrasonic detection responds to gas turbulence, not refrigerant chemistry.

3. A technician pressurizes a system with dry nitrogen in the afternoon and comes back the next morning to find that the pressure has dropped noticeably. What has to be checked before calling that a leak?

  • The ambient temperature at both readings, because a colder system holds less pressure even with no leak at all
  • BWhether the nitrogen cylinder still had pressure left in it when the system was charged for the test

    What remains in the supply cylinder says nothing about what happened inside the system after it was charged, valved off and disconnected. The cylinder could be empty and the standing test still be perfectly valid.

  • CWhether the system was left with the compressor running overnight, which would have circulated the nitrogen charge

    A system holding a nitrogen test charge is not running and must not be run. Circulating nitrogen with the compressor would be a separate and serious problem, not an explanation for an overnight pressure change.

  • DThe oil level in the compressor crankcase, since oil absorbs nitrogen and lowers the standing pressure

    Oil does not absorb enough nitrogen to move a gauge, and crankcase level is unrelated to what a sealed volume holds. The change here is about temperature, not about where the oil is sitting.

Why A is correct

Pressure and temperature move together for a gas held in a fixed volume. Without a temperature reading at both ends of the test, a pressure change cannot be attributed to a leak, and rooftop temperature swings between afternoon and early morning are easily large enough to move the gauge.

What this question is testing

This item tests understanding that a standing pressure test compares pressure at matched temperatures, and that an unexplained drop is not automatically evidence of a leak.

On the job

Technicians who skip the temperature reading chase leaks that do not exist, or worse, dismiss a real leak because the pressure drop looked small. The habit is simple: write down the gauge pressure and the ambient temperature when the test starts and again when it ends, right on the service ticket. On multi-day tests, a data-logging gauge takes the argument out of it entirely and gives the customer a record.

Memory technique

Cold gas reads low. Write down the temperature or the test is just a guess.

Exam tip

Standing pressure test questions almost always hinge on temperature. Record it at both readings or the test proves nothing.

Where to look it up

Leak repair verification under 40 CFR Part 82, Subpart F relies on valid test results; a standing pressure test requires matched temperature readings to be interpretable.

4. A commercial unit has been topped off with refrigerant three separate times in one cooling season instead of having its leak located and repaired. What is wrong with continuing that practice?

  • The refrigerant keeps escaping into the atmosphere, and adding charge is not an accepted substitute for repairing the leak
  • BAdding charge more than twice in a single cooling season voids the technician's certification for the rest of the year

    Certification is not revoked by counting recharges, and no seasonal limit of that kind appears in the rule. The obligation is to repair leaks, and enforcement runs against the owner and the servicing contractor.

  • CTopping off is permitted only on systems charged with a chlorine-free substitute refrigerant rather than an older one

    The venting prohibition and the leak repair requirements were extended to substitutes, so a chlorine-free refrigerant gets no easier treatment. Refrigerant chemistry never creates permission to keep replacing a lost charge.

  • DRefrigerant added on top of an existing charge cannot mix properly with the compressor oil, so the added pounds never circulate

    Added refrigerant mixes with the existing charge and circulates with the oil normally. The objection is not a mixing problem inside the machine, it is the refrigerant that keeps leaving through the unrepaired leak.

Why A is correct

Refrigerant that leaks out is a release, and the rules require leaks to be found and repaired rather than compensated for with more refrigerant. Repeated recharging also means the owner pays for refrigerant repeatedly while the equipment operates undercharged between visits, which shortens compressor life.

What this question is testing

The item checks that the candidate treats leak repair as the required response to refrigerant loss and can reject plausible-sounding but invented rules about recharging.

On the job

This is the single most common conversation on a commercial service call, because a repair costs more than a jug of refrigerant on the day. The counterargument that actually lands with an owner is money over a season: three recharges plus three trip charges usually exceeds the cost of finding and fixing the leak, and the equipment runs better in between. Documenting each recharge on the ticket also builds the record that justifies the repair.

Memory technique

Refrigerant is not a consumable. If you are adding it every season, you are venting it every season.

Exam tip

On any question about repeated topping off, the correct answer is the one about repairing the leak. Distractors invent penalties or chemistry problems.

Where to look it up

40 CFR Part 82, Subpart F prohibits knowingly venting and requires leaks to be repaired and the repairs verified.

5. A pressure relief valve on a rack receiver lifted during a hot spell and has been losing refrigerant slowly ever since, even though system pressure is now normal. What is the correct repair?

  • ATighten the valve down against its seat until the weeping stops

    Adjusting a relief valve changes the pressure at which it protects the vessel and voids its listing. It is not a field-adjustable component.

  • BLeave it in service, since it will reseat once cooler weather returns

    The weep will continue in any weather, because it is caused by a damaged or fouled seat rather than by current system pressure.

  • Replace the relief valve, because a valve that has discharged may not reseat
  • DCap the valve outlet so the escaping refrigerant is contained in the system

    Capping the outlet disables the vessel's overpressure protection. That converts a refrigerant loss into the possibility of a receiver rupture.

Why C is correct

Relief valves are not designed to reseal reliably after they have relieved. Anything that passed the seat can hold it open, and the seat can deform under the discharge. A weeping valve is therefore replaced rather than adjusted, which restores both a tight refrigerant circuit and a working overpressure protection for the receiver.

What this question is testing

This tests the correct disposition of a safety device after it has operated, which sits at the intersection of leak repair and safe service practice. The distractors are all things technicians are tempted to do when a valve weeps on a busy day.

On the job

Relief valve weeps are easy to miss because the discharge is often piped away from the machine and the loss is slow. On a hot roof after a condenser fan failure, a lifted valve can be the whole explanation for a system that has been low ever since. Recording the discharge when it happens and scheduling the valve for replacement is the practice that keeps a one-time event from becoming a season of losses.

Memory technique

A relief valve is a one-shot bodyguard. Once it takes the hit, it retires.

Exam tip

Anything that opened to protect the system is replaced, not readjusted. Never cap a relief path.

Where to look it up

A pressure relief valve that has discharged may not reseat tightly and should be replaced rather than adjusted or capped.

6. Oil is found under the brass cap of a service valve stem on a rooftop unit that loses a small amount of charge each season. What is leaking there?

  • AThe brazed joint where the valve body meets the liquid line

    A brazed joint at the valve body would show oil at the joint itself, on the outside of the valve, rather than collecting inside the stem cap.

  • The packing around the valve stem, which seals against the stem shaft
  • CThe Schrader core in the gauge port on the side of the valve body

    A leaking gauge port core shows oil at the port, under the separate port cap. That is a different cap on a different part of the valve.

  • DThe threads of the cap itself, which are not a sealing surface

    Cap threads are not a pressure joint on their own, but the cap with its gasket is the secondary seal, which is why oil is found trapped beneath it.

Why B is correct

The stem is a rotating shaft passing through the pressure boundary, sealed by packing that wears and loosens with every use. Oil appearing under the cap is refrigerant and oil working past that packing. The valve cap is the secondary seal that catches it, which is why the cap must be refitted and tightened after every service call.

What this question is testing

This tests the ability to locate a leak precisely from where the oil is found, and it reinforces why the small hardware on a service valve is treated as part of the pressure boundary rather than as an accessory.

On the job

Service valves get operated on every call, and stem packing is the part of a rooftop unit most directly worn by the technician's own work. Backing a stem out fully to the back seat and then giving it a quarter turn in is the habit that keeps the packing sealed during operation. The caps themselves are frequently missing on old equipment, and putting proper caps back on is a real reduction in seasonal losses across a site.

Memory technique

The cap is not a hat, it is a second door. Oil behind it means the first door leaks.

Exam tip

Oil under a cap means the cap was doing its job as a seal. The leak is at whatever the cap covers.

Where to look it up

Service valve stem packing seals a rotating shaft and weeps with wear; the cap is the secondary seal.

25 more in the bank

Answers and explanations for these are in the app.

  • A slow R-410A leak has been narrowed down to a cluster of flare fittings at the outdoor unit, and the technician now needs to identify which single fitting is losing charge. Which method points to the leaking joint most directly at that spot?
  • A leak on the liquid line of a 60-ton R-410A rooftop unit has been brazed shut. What does the technician still owe on that repair before the unit is considered properly returned to service?
  • A technician finds a halide leak detector torch in an older toolbox and wonders whether to use it while looking for a leak on an R-410A system. Why is that tool the wrong choice today?
  • A system loses part of its charge over the course of several months, but a careful search during a service call turns up nothing at all. Which detection approach fits that situation best?
  • A system has been pressurized with dry nitrogen for a leak test, and a technician sweeps an electronic refrigerant detector along every joint without getting a single alarm. What does that result tell the technician?
  • After brushing soap solution over a unit that loses a small amount of charge every year, a technician sees bubbles forming right at one of the service ports. What is the appropriate repair?
  • A small leak is suspected somewhere inside an evaporator coil, in tubing buried among the fins and the rows of the bundle. What makes that kind of leak so hard to pin down?
  • A low-temperature system is undercharged enough that the low side operates below atmospheric pressure whenever the compressor runs. What happens at a leak on that part of the system?
  • A technician has finished locating and repairing a leak on a large commercial refrigeration system. What belongs in the service record for that visit?
  • A verification test performed after a leak repair shows that the repaired joint is still losing refrigerant. What is the correct response to that result?
  • An electronic leak detector alarms continuously as soon as it is switched on inside a closed mechanical room. What should the technician do before trusting any reading from it?
  • A brazed joint made without flowing nitrogen through the tubing develops a pinhole leak after a season of operation, and the system also shows a restricted metering device. What did the missing nitrogen contribute to?
  • A technician is about to set the regulator for a dry nitrogen leak test on a split system that includes an accumulator and a receiver. What determines how high that test pressure may be set?
  • A technician is trying to use soap bubble solution to locate a leak on a rooftop unit on a windy and hot afternoon. What limits that method under those conditions?
  • A leak above the action level is found on an industrial process refrigeration system, and the repair cannot be made without shutting down the process the system serves. How much time does the regulation allow for that repair?
  • An electronic leak detector that uses a heated sensing element has grown sluggish and misses leaks the technician can find with bubbles. What does that instrument most likely need?
  • A leak detector's specification sheet gives a sensitivity figure stated as a weight of refrigerant per year. What does that figure describe about the instrument?
  • A rack uses an open drive compressor with a motor mounted alongside and a belt between them. Which point on that compressor is the one most likely to leak refrigerant?
  • A restaurant near the ocean has lost two evaporator coils in five years, each to tiny pinholes scattered through the copper tubing rather than at any joint. What condition produces that pattern?
  • A small diameter equalizer tube on a rack is found weeping refrigerant exactly where it crosses a steel frame member, with the copper worn bright and thin at that point. What has caused the leak?
  • A technician considers injecting a chemical sealing additive into a commercial system that keeps losing a small amount of charge. What is the practical objection to putting that product into this system?
  • A leaking joint on a commercial system has been brazed and the technician now has nitrogen, a vacuum pump and the refrigerant charge available. In what order should those three steps be carried out?
  • A semi-hermetic compressor that has been opened for valve plate work twice now shows an oil film along the seam between the head and the body. What should the technician do about that joint?
  • A technician adds refrigerant to a large commercial appliance during a service call while a leak search is still to be scheduled. What information about that addition belongs on the service record?
  • A water cooled condensing unit loses charge steadily but no oil stain or detector reading can be found anywhere on the machine or its piping. What should the technician suspect about a tube failure in the condenser bundle?

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