A helper suggests running the appliance's own compressor to assist the vacuum pump in pulling the system down after a repair. Why is that the wrong move?
Correct Answer
C) Running a compressor in a deep vacuum can arc across the motor terminals and burn the windings, and any leak pulls air and moisture straight into the system
A hermetic or semi-hermetic compressor depends on refrigerant vapor for motor cooling and for the dielectric strength between its internal electrical connections. Under a deep vacuum both are gone, and voltage can arc across terminals that are perfectly safe at normal pressure, burning the motor. The compressor is also running with no refrigerant to carry oil, and any leak in the system feeds atmosphere in rather than letting refrigerant out. The vacuum pump is the only tool for this job.
Why This Is the Correct Answer
Vapor inside a compressor shell provides both cooling and electrical insulation. Pull that vapor away and the same voltage that was safe before can arc, which is how a technician turns a working compressor into a burnout in a few seconds. On top of that, an evacuating system with a leak admits air and moisture, undoing the whole purpose of the pull.
Why the Other Options Are Wrong
Option A: The compressor would push whatever refrigerant is left in the system back into the recovery cylinder instead of helping the vacuum pump pull the whole system down
By this point the repair is finished, the recovery cylinder is off the system, and nothing is left inside to push anywhere. The objection is what a deep vacuum does to the motor, not where refrigerant would end up.
Option B: The compressor cannot produce a vacuum deep enough to register on a micron gauge, so it adds nothing to what the pump is doing
Depth of vacuum is not the objection, and a running compressor would in fact move the gauge. The reason to leave it off is that operating it in a vacuum destroys the motor windings.
Option D: The compressor's own oil pump would draw vacuum pump oil back into the crankcase and flood it partway through the evacuation
Vacuum pump oil stays in the pump; nothing carries it up the hoses and into the compressor's crankcase. The two oil systems are not connected to each other at any point during evacuation.
Memory Technique
No vapor, no insulation. A compressor in a vacuum is an arc waiting to happen.
Reference Hint
40 CFR 82.156 requires evacuation using certified equipment and a vacuum pump. Running the appliance compressor under vacuum is a known cause of motor burnout.
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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On a compressor changeout the technician first pulls the charge into a cylinder, and later, after the new compressor is brazed in, pulls the system down with a vacuum pump. What separates those two operations?
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