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Recovery & Evacuation — EPA 608 Practice Questions

45 questions · 33% of the Type III — Low Pressure exam

Worked questions

1. Why is the recovery level for a low-pressure appliance stated as an absolute pressure instead of as inches of vacuum on a compound gauge?

  • An absolute reading shows how close the machine is to a perfect vacuum, and a compound gauge cannot resolve that range
  • BA compound gauge cannot be connected to a machine that spends its running time below atmospheric pressure

    A compound gauge attaches to the machine without any trouble. The objection is resolution: the last inch of its scale spans the entire range the required recovery level lives in.

  • CAbsolute readings are required only on machines that were manufactured before nineteen ninety three, when the levels changed

    Manufacture date does change the required recovery level for some equipment classes, which is where this idea comes from, but it never changes which unit of measure the level is stated in.

  • DInches of vacuum start reading backward once the pressure falls far below atmospheric pressure

    A gauge does not read backward below atmospheric pressure. It simply runs out of usable scale long before the machine reaches the required level, which is why an absolute reading is used.

Why A is correct

Absolute pressure is measured from a perfect vacuum, so the numbers stay meaningful all the way down. A compound gauge measures relative to atmosphere and crowds the entire deep vacuum range into the last fraction of its dial, where two very different conditions look identical. Only an absolute reading can confirm the machine reached the required level.

What this question is testing

This tests whether you understand the measurement itself rather than just the number. The exam wants to confirm you know why the low-pressure standard is written in absolute terms and what instrument that implies. It also measures whether you can name the practical consequence, which is that a compound gauge cannot document compliance on this equipment.

On the job

Bring the wrong instrument and you will swear the job is done while the machine still holds a substantial amount of refrigerant. The compound gauge pins at the bottom of its scale and stops telling you anything, so the technician disconnects, opens the machine, and vents whatever is left into the room. An electronic absolute reading instrument costs little compared to a chiller charge and is the only way to honestly document that the required level was reached before the machine was opened.

Memory technique

Absolute counts up from nothing; gauge counts from the room. Deep vacuums need the one that starts at nothing.

Exam tip

Absolute means counted up from a perfect vacuum. Gauge or compound readings are counted from atmosphere, and they run out of resolution first.

Where to look it up

Low-pressure appliance recovery levels are expressed as absolute pressure because a compound gauge has no resolution in the deep vacuum range.

2. How can a technician speed up removal of the last of the vapor from a cold low-pressure machine without risking the tubes?

  • AOpen the machine briefly to the room so air pressure pushes the vapor out to the hose

    Opening the machine to the room lets air in and lets refrigerant out, which defeats the purpose of recovery and is a prohibited release. Atmospheric pressure is not a recovery tool.

  • BRun the chiller's compressor while the recovery machine is connected to the shell

    Running the chiller's own compressor during recovery risks damaging it with no oil return and no load, and it does nothing to move the last of the vapor out of the machine.

  • Circulate warm water through the tubes to raise the refrigerant's saturation pressure
  • DAdd nitrogen to the shell to sweep the remaining vapor toward the recovery hose faster

    Adding nitrogen mixes a non-condensable into the charge being recovered, contaminating the cylinder and leaving the machine working against a partial pressure it cannot remove.

Why C is correct

Warm circulating water raises the temperature of the refrigerant remaining in the vessel, which raises its saturation pressure and increases the amount of vapor the recovery machine can move per minute. Because the water is warm and flowing, the freeze hazard disappears at the same time, so the technique solves two problems at once.

What this question is testing

This tests applied understanding of the pressure temperature relationship during recovery. It also checks that you reject the shortcuts that vent refrigerant or contaminate the recovery cylinder. It also measures whether you reject shortcuts that vent refrigerant or introduce non-condensables, both of which look attractive when a job is running long.

On the job

Every plant that does this work regularly has a way to feed warm water or condenser water through the evaporator bundle during recovery. It turns a job that stalls out overnight into one that finishes the same day, and it keeps the freeze protection built in. If no warm water source exists, the fallback is a very long, patient vapor pull with the water pumps left running so nothing freezes while you wait.

Memory technique

Warm water is your friend twice: it makes the vapor move and it keeps the tubes from splitting.

Exam tip

Any answer that involves venting to the room or adding nitrogen into refrigerant you plan to recover is wrong on the exam and wrong in the field.

Where to look it up

Heat raises saturation pressure, so warm circulating water speeds vapor recovery and prevents freezing at the same time.

3. How does a technician tell when a recovery cylinder taking an R-123 charge has reached its filling limit?

  • By keeping the cylinder on a scale and watching the net weight
  • BBy waiting for the cylinder pressure to reach its marked service pressure

    The service pressure marked on a cylinder is a design rating, not a fill indicator, and a low-pressure refrigerant will never approach it at room temperature.

  • CBy feeling the outside of the cylinder for a frost line

    Frost lines can suggest a liquid level on some cold refrigerants, but R-123 near room temperature produces no reliable frost line.

  • DBy counting the running hours logged on the recovery machine

    Run time varies with vapor density, hose size and machine condition, so it cannot be converted into pounds transferred. Two identical machines can take very different amounts of time to give up the same weight.

Why A is correct

Weight is the only dependable indicator with a low-pressure refrigerant, because its vapor pressure at room temperature is too low to move the cylinder gauge meaningfully. Working from tare weight and rated capacity lets the technician stop at the correct fill level rather than guessing.

What this question is testing

This tests measurement method rather than the fill limit number, and it checks that you understand why pressure based judgment fails with low-pressure refrigerants. It measures whether you can select a measurement method appropriate to the refrigerant rather than reaching for the pressure gauge habit built on high-pressure work.

On the job

Put the cylinder on the scale before you start and leave it there. On a long chiller recovery you may go through several cylinders, and the transitions are where mistakes happen: someone swaps cylinders, forgets to re-tare, and overfills. An overfilled cylinder of any refrigerant is a serious hazard if it warms up, because a liquid full cylinder has no vapor space to absorb thermal expansion. The scale is cheap insurance on a job that already takes all day.

Memory technique

No pressure, no clue. Weigh it, because the gauge will lie to you all day.

Exam tip

When a question involves a low-pressure refrigerant and a cylinder, expect the answer to involve weight. Pressure based methods do not work here.

Where to look it up

Recovery cylinder fill is judged by net weight on a scale, because low-pressure refrigerant develops almost no pressure at room temperature.

4. A technician has just taken a water-contaminated charge out of a chiller with a split tube, and the next job that day is a clean machine across town. What has to be done to the recovery unit first?

  • AIts high pressure switch has to be reset so that the next machine can be pulled down deeper

    Resetting a pressure switch has nothing to do with contamination, and a recovery unit's protective switches are not what limits how deep it can pull.

  • Its filters and its oil have to be changed so that the next machine is not contaminated
  • CIts nameplate has to be relabeled so that the next machine's paperwork shows the refrigerant

    The nameplate identifies the equipment, not its last load. Paperwork does nothing about the moisture and acid actually sitting inside the machine.

  • DIts cylinder fittings have to be swapped so that the next machine gets a clean hose set

    New hoses are worth having, but the contamination that matters is inside the recovery unit's own filter, lines and oil, and swapping fittings does not touch it.

Why B is correct

Recovery equipment carries whatever it has just pumped. Moisture and acid soak into the compressor oil and load the filter, and both will be pushed into the next appliance the unit is connected to. Changing the oil and filter and evacuating the machine between jobs is the standard practice that keeps contamination from moving between customers.

What this question is testing

This tests cross-contamination awareness, which sits between the regulations and good practice. The exam looks for candidates who think about what the equipment carries between jobs rather than treating the recovery unit as a neutral pump.

On the job

Shops that do chiller work keep a spare filter core and a quart of oil on the truck for exactly this. The technician who skips it on a Friday afternoon can put a compressor burnout's worth of acid into a machine that was healthy that morning, and the failure will not show up until the following season. Some contractors keep a separate recovery unit tagged for contaminated work so the question never comes up.

Memory technique

The recovery machine remembers its last job. Change its oil and filter before it tells the next customer about it.

Exam tip

Whatever came out of the last machine is still in the recovery unit until you change the filter and the oil.

Where to look it up

Recovery equipment must be maintained so it does not carry contamination from one appliance into the next.

41 more in the bank

Answers and explanations for these are in the app.

  • In what unit is the required final recovery vacuum for a low-pressure appliance normally expressed?
  • What should a technician do about the water in the chiller tubes before pulling a deep vacuum on the machine?
  • Which reading is the warning that water remaining in the tubes may be about to freeze and split them?
  • To what level may a recovery cylinder be filled when refrigerant is taken out of a low-pressure appliance?
  • Which instrument does a technician use to confirm that a low-pressure appliance has reached the required recovery level?
  • In what order does a technician remove the charge from a low-pressure chiller to keep the job from dragging on?
  • Many large low-pressure chillers are built with an onboard device for moving the charge out of the machine. What is that device called?
  • What is the result if standing chilled water is left in the tubes and freezes while a deep vacuum is pulled on the machine?
  • A technician reaches the required level, closes the machine up, and finds refrigerant pressure building again hours later. What is the most likely reason?
  • What makes the vapor phase of recovery from a low-pressure chiller so much slower than from a comparable high-pressure machine?
  • What hose arrangement keeps the vapor phase of a low-pressure recovery from dragging on longer than necessary?
  • After the required recovery level is reached, how does a technician confirm the reading is genuine rather than a temporary pump down?
  • What does a technician use to bring a low-pressure machine back up to atmospheric pressure before opening it for tube work?
  • Why does a technician introduce the first portion of the charge into a low-pressure machine slowly?
  • What must a technician do with the charging hoses before opening them to a machine that is holding a deep vacuum?
  • What kind of container may a technician pump a recovered low-pressure refrigerant charge into?
  • After a low-pressure machine is closed back up following an open repair, what has to happen before the charge goes in?
  • A technician has finished pulling the charge out of an R-123 centrifugal chiller and now has to decide when the machine may be opened. What level must the appliance itself reach first?
  • Two low-pressure chillers in one plant both need their charges recovered, one built in nineteen eighty-eight and the other in nineteen ninety-eight. How do the required evacuation levels for the two machines compare?
  • A technician's electronic vacuum gauge reads in microns rather than in millimeters of mercury. Which reading on that gauge corresponds to the level a low-pressure appliance is required to reach?
  • An operator asks how the required low-pressure recovery level compares with the vacuum scale printed on an ordinary compound gauge. Roughly how far below atmospheric pressure does that level sit at sea level?
  • A plant operator suggests leaving the chiller's purge unit running overnight to empty the machine so the crew can open it in the morning. Why will that plan not work?
  • The purge unit on an R-123 chiller has failed and its compressor has to be replaced. What has to happen to the refrigerant sitting inside that purge unit before it is opened up?
  • A chiller is fitted with a factory pump-out unit and a storage tank, and the entire charge is now sitting in that tank. What still has to be done before the machine's waterbox covers come off?
  • An evaporator tube splits and chilled water floods into the refrigerant side of a low-pressure machine. What happens to the refrigerant that is recovered out of that machine?
  • Several gallons of water got into the shell of a low-pressure chiller through a ruptured tube. Beyond repairing the tube, what has to be done to that machine before a charge goes back into it?
  • During the final pull down on a low-pressure chiller the technician's absolute pressure gauge is holding steady at forty millimeters of mercury. What does that reading mean for the job?
  • Once the liquid is out of a low-pressure chiller, where should the technician make the connection for the vapor phase of the recovery?
  • An owner objects to the rental line for a certified recovery unit, arguing that his refrigerant is being put right back where it came from. What does the rule require for taking it out?
  • A rebuilt low-pressure chiller is ready to take its charge back after a complete retube. How does the technician establish how much refrigerant to put into it?
  • A low-pressure chiller has taken on several gallons of water from a burst tube, and that water is standing in the bottom of the evaporator shell. What has to happen before a vacuum pump goes on the machine?
  • Recovery from a two-vessel low-pressure chiller is running slowly with a single hose on the evaporator. Which connection change usually shortens the job the most?
  • After a low-pressure machine has reached the required level and the charge is out in cylinders, the technician wants to pull it deeper still to dry it out. Is a plain vacuum pump allowed for that?
  • Some jobs on a chiller count as a major repair under the refrigerant rules, which changes what a technician is allowed to do with a badly leaking machine. Which job falls into that category?
  • An owner asks how many pounds of refrigerant the rules allow to be left inside a chiller once the recovery has been signed off. What is the correct answer to give him?
  • A low-pressure chiller is several hundred pounds light and the plant wants refrigerant added without any other work being done. What does the evacuation requirement mean for that job?
  • During recovery from a centrifugal chiller the technician needs to know when the liquid phase has finished and the slow vapor phase is starting. What tells him that?
  • A technician remembers that the evacuation table splits appliances at a two hundred pound charge. How does that split apply to a chiller holding one hundred and fifty pounds of R-123?
  • A technician used to reciprocating equipment asks why the chiller's own compressor cannot simply be run to push the charge over into the condenser. What is the reason?
  • As the recovery unit begins pulling the charge out of a chiller, what should the technician do with the machine's purge unit?
  • A chiller is being scrapped and the owner wants to skip the recovery because the machine has held a vacuum for two years and is probably empty already. What has to be done?

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