Recovery on a rooftop unit is crawling along on a very cold day, with the appliance and its remaining charge sitting at outdoor temperature. How does the cold slow the job down?
Correct Answer
B) The refrigerant remaining in the cold appliance vaporizes slowly, so the machine has very little vapor available to move
Saturation pressure follows temperature. A cold appliance holds its remaining refrigerant at a low pressure, and the liquid clinging in the evaporator, the accumulator and the oil boils off slowly because there is little heat available to drive it. The recovery machine can only move what reaches it as vapor, so the job stretches out. Technicians speed it up by adding heat to the appliance, for example by running the indoor fan across the coil, and by keeping the recovery cylinder cooler than the appliance so the pressure difference stays in their favor.
Why This Is the Correct Answer
Vapor has to be generated before it can be pumped. In a cold appliance the liquid refrigerant sits at a low saturation pressure with almost no heat flowing into it, so it boils off slowly and the recovery machine spends its time pumping very little mass. Adding heat to the appliance is the direct fix.
Why the Other Options Are Wrong
Option A: Cold refrigerant thickens and will not pass through the recovery machine's filter drier until it warms
Filter driers do not care about temperature. They restrict flow when they are loaded with debris or moisture, and refrigerant does not thicken into something a drier cannot pass on a cold rooftop.
Option C: The recovery cylinder has to be warmed above the appliance temperature before any transfer can begin, and a cold cylinder stalls the job
The cylinder should be the cold end of the transfer, not the warm end. Warming it raises its pressure and pushes back against the machine, which is the opposite of what a slow recovery needs.
Option D: Recovery machines shut themselves down automatically once the ambient temperature drops below fifty degrees
No such ambient lockout exists. Recovery machines carry high and low pressure switches and a thermal overload on the motor, none of which watch the outdoor temperature.
Memory Technique
Warm the system, chill the cylinder. Refrigerant runs from hot to cold.
Reference Hint
Recovery is governed by saturation pressure and temperature. 40 CFR 82.156 sets the requirement to recover; the physics sets the pace.
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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Previous Question
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?
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