A technician is out of nitrogen and considers using the oxygen cylinder from the torch outfit to pressurize a system for a leak search. Why must that never be done?
Correct Answer
D) Oxygen under pressure in contact with refrigerant oil can ignite and explode violently
A refrigeration system is full of oil. Oxygen under pressure in contact with a hydrocarbon oil can ignite from nothing more than the heat of compression, and the result is an explosion rather than a fire. This is one of the few absolute rules in the trade. Compressed shop air is also unacceptable, for a different reason: it carries water vapor and compressor oil into the system. Dry nitrogen fed through a regulator is the only correct gas for pressurizing a refrigeration system.
Why This Is the Correct Answer
Oxygen dramatically accelerates combustion, and oil is fuel. Under pressure the combination can ignite without any spark or flame present, driven by the heat of compression alone, which is why oxygen is never permitted anywhere near a system containing oil.
Why the Other Options Are Wrong
Option A: Oxygen molecules are small enough to pass through copper tubing walls and escape
Gases do not migrate through the wall of copper tubing, and molecular size has nothing to do with the prohibition. The hazard from oxygen in a refrigerant circuit is chemical and immediate.
Option B: Oxygen leaves a residue behind that ruins the compressor motor windings when it is charged
Oxygen leaves no residue on windings or anywhere else. Treating this as a slow contamination problem misses the point, because the hazard shows up during the pressure test itself.
Option C: Oxygen interferes with the readings from an electronic leak detector during the test
Detector interference is trivial next to the real hazard and is not why oxygen is forbidden. An electronic detector is calibrated for refrigerant and is simply not the concern here.
Memory Technique
Oxygen plus oil plus pressure equals a bomb. The green bottle never touches a refrigeration system.
Reference Hint
Only dry nitrogen through a regulator may be used to pressurize a refrigeration system. Oxygen with oil under pressure is an explosion hazard.
More epa-608-type-2 Questions
A walk-in cooler condensing unit holds a full charge of twenty-five pounds of R-404A, which is below the fifty pound threshold that brings an appliance under the leak repair provisions. What still applies to this unit?
An office building has thirty water source heat pumps on a common water loop, and each one left the factory assembled, hermetically sealed and charged with four pounds of R-410A. How is one of those units classified?
A data sheet for an unfamiliar refrigerant lists a boiling point of about fifty-five degrees Fahrenheit at atmospheric pressure. What does that tell a technician holding Core and Type II certification?
A technician holds Core, Type I and Type III certification and is sent to recover the charge from a twenty ton rooftop unit charged with R-410A. What does that combination of sections allow on this job?
A fleet garage technician holds only the vehicle air conditioning certification issued under Section 609 and is asked to recover the charge from the shop's own rooftop air conditioner. What does that credential allow?
A split system's outdoor unit, indoor coil and the line set the installer ran and brazed between them are being considered. For the purposes of the refrigerant rules, what makes up the appliance here?
On a new installation the line set is brazed to a factory charged outdoor unit and an indoor coil shipped under a nitrogen holding charge, with the outdoor unit's service valves still closed. What does the recovery requirement call for before that brazing?
A rooftop unit's data plate has weathered until the charge figure cannot be read, and the technician needs the full charge to place the appliance under the evacuation and leak provisions. Where should that figure come from?
A computer room air conditioning unit holds forty pounds of R-407C and connects to a remote air cooled condenser through refrigerant piping run and brazed by the installer. How is that unit classified?
A shop's office manager, who holds no technician certification, is sent to a supply house to pick up a new recovery machine for the commercial crew. What does the sales restriction require at that counter?
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