The repair on a household refrigerator is finished, the system has been evacuated, and the technician is ready to put refrigerant back in. How is the correct amount determined on a capillary tube small appliance?
- ABy running the unit and adding vapor until suction pressure matches a chart for the refrigerant
Suction pressure on a capillary tube system moves with box temperature and load, so matching a chart figure says nothing definite about how many ounces are inside.
- BBy adding refrigerant until frost reaches the end of the evaporator with the door closed
Frost patterns shift with door openings, ambient temperature and how long the unit has run. Chasing frost routinely overcharges a small system by a large fraction.
- CBy filling until the sight glass at the drier clears of bubbles at normal room temperature
Small appliances almost never have a sight glass, and on a capillary tube system a clear glass would say nothing about whether the weighed charge is right.
- By weighing in the exact amount the data plate lists, using an accurate charging scale
Why D is correct
Small appliances meter refrigerant through a capillary tube and hold no reserve charge, so the correct amount is a specific weight rather than a pressure to chase. That weight is on the data plate. Charging by scale reproduces the factory figure exactly, which is why every manufacturer's service literature for a sealed system gives a charge in ounces or grams rather than an operating pressure.
What this question is testing
This item tests service practice on the recharge step that follows recovery and repair. It checks that you recognise a capillary tube system as critically charged, that you know where the correct amount comes from, and that you can rule out indirect indicators that work only on larger systems.
On the job
The charging scale is the most used tool on a sealed system repair after the recovery machine. Cabinets in the field carry charges as small as four to six ounces, so the scale has to resolve tenths of an ounce and sit on a level surface out of the draft. Techs weigh the charging cylinder before and after, or set the scale to count down. Overcharging a refrigerator by an ounce shows up as a warm box with a flooded evaporator and a compressor running cool; undercharging shows up as a partially frosted coil and long run times. Neither is fixed by guessing.
Memory technique
Capillary tube means no reserve. No reserve means no guessing. Weigh it.
Exam tip
Anything described as factory sealed with a capillary tube is charged by weight. If a choice involves reading a pressure or watching frost, it belongs to a larger system with an adjustable metering device.
Where to look it up
Small appliances are critically charged. Weigh in the exact data plate charge with a scale.