Nine ounces came out of a refrigerator whose data plate calls for a ten ounce charge, and the technician plans to put that same recovered refrigerant back in after the repair. What does the recharge require?
- AReturning the nine ounces and running the unit, since it came out of this same cabinet
A refrigerant's origin does not make an incomplete charge correct. Nine ounces in a ten ounce system runs warm with long cycles no matter where those nine ounces came from.
- BReturning the nine ounces and adding vapor until the suction pressure looks correct
Suction pressure on a capillary tube system tracks load and ambient rather than charge, so it is far too coarse to land on the last ounce.
- CReturning the nine ounces and topping up until frost covers the whole evaporator
Frost patterns shift with door openings and room temperature, and chasing frost on a small system routinely produces an overcharge.
- Returning the nine ounces plus enough more to reach the full ten ounce data plate charge
Why D is correct
The recovery requirement and the charging requirement are two different numbers doing two different jobs. Recovery is satisfied at a percentage of the charge or at a vacuum reading; charging is satisfied only at the exact weight the data plate specifies. Since recovery always leaves a portion behind in the oil, the recovered refrigerant has to be supplemented from a clean cylinder of the same refrigerant until the scale reads the full charge.
What this question is testing
This item tests whether you can carry the reason behind the percentage recovery requirement forward into the recharge step. It checks that you do not confuse the amount recovered with the amount the appliance needs, and that you know the data plate weight governs the charge.
On the job
This is where the physics from the recovery side shows up as money and callbacks. Techs who assume the cylinder holds the whole charge send units back out an ounce light, and the customer calls back a week later about a warm crisper drawer. The van needs a small cylinder of clean refrigerant of each type in common use, alongside the recovery cylinders, precisely so the shortfall can be made up. Keep the recovered material and the clean material clearly separated, because a mixed cylinder is worth nothing to anybody.
Memory technique
What comes out is a percentage. What goes back in is the whole number.
Exam tip
Recovery is a percentage, charging is a weight. Whenever a stem gives you both an amount recovered and a data plate figure, the gap is the point of the question.
Where to look it up
Recovery leaves refrigerant behind in the oil, so the recharge is topped up to the full data plate weight with a scale.