EPA 608 practice questions, with worked answers

C: No more than 80% of its capacity. The 20% of space left lets the liquid expand as the temperature rises without hydrostatic pressure building up and rupturing the cylinder.

The trap: Filling to 100%. Liquid refrigerant expands as it warms, and a full cylinder can rupture.

D: September 2028. Refillable DOT recovery cylinders must be retested every 5 years: September 2023 + 5 years = September 2028. Do not fill a cylinder that is out of date.

C: A2L: lower toxicity, lower flammability. R-32 is in group A2L. The letter is toxicity (A lower, B higher); the number is flammability (1 no flame propagation, 2L lower flammability, 3 higher flammability).

A: 99.7 psia. A gauge reads pressure above the atmosphere. Absolute pressure adds atmospheric pressure at sea level: 85 + 14.7 = 99.7 psia.

1. psia = psig + 14.7.
2. 85 + 14.7 = 99.7.
3. So about 99.7 psia.

The trap: Subtracting 14.7 (70.3). That converts the wrong way.

A: Recycling cleans refrigerant for reuse, often on site; reclaiming reprocesses it to new-product purity, verified by chemical analysis. Recovering is removing refrigerant into a container. Recycling cleans it (oil separation, filter-driers) for reuse, often in the same shop. Reclaiming reprocesses it to the purity of new refrigerant, confirmed by chemical analysis, usually at a certified reclaimer.

1. Recover: take it out and store it.
2. Recycle: clean it for reuse.
3. Reclaim: reprocess it to new-product purity and test it.

The trap: Treating "recover" and "reclaim" as the same. Recovery is only the removal.

A: 5 pounds or less of refrigerant. A small appliance is fully manufactured, charged and hermetically sealed in a factory with five pounds or less of refrigerant.

The trap: Using 15 or 50 pounds, the leak repair and other thresholds. A small appliance is 5 pounds or less.

D: 24 pounds. Fill a recovery cylinder to no more than 80% of its capacity: 30 × 0.8 = 24 pounds. The space left lets the liquid expand safely.

B: No; it holds more than 5 pounds. A small appliance is manufactured, charged and hermetically sealed in a factory with 5 pounds or less. This one was factory sealed with 6 pounds, so it is not, because the charge is over 5 pounds.

D: HC (hydrocarbon). R-290 is propane: a hydrocarbon, which is highly flammable. Knowing the type tells you which recovery cylinder and precautions to use.

A: 80% of the refrigerant, or a 4-inch Hg vacuum. For small appliances, equipment made after November 15, 1993 must recover 90% when the compressor works and 80% when it does not, or achieve a 4-inch Hg vacuum. This compressor does not run, so 80%.

1. Equipment date: 2015, after November 15, 1993.
2. Compressor: not running.
3. Rule: 80%, or a 4-inch Hg vacuum.

The trap: Using 90%. That figure is for a working compressor.

A: 0.5625 pound. There are 16 ounces in a pound: 9 ÷ 16 = 0.5625 pound, well under the 5-pound small appliance limit.

1. 16 ounces = 1 pound.
2. 9 ÷ 16 = 0.5625.
3. So 0.5625 pound.

The trap: Dividing by 10 (0.9 pound). Ounces and pounds are not decimal.

C: 10% per year. Since January 1, 2019, the thresholds are 10% for comfort cooling, 20% for commercial refrigeration and 30% for industrial process refrigeration.

The trap: Swapping the thresholds. Comfort cooling is the strictest at 10%; commercial refrigeration is 20% and industrial process 30%.

A: 3°F. Subcooling = saturation temperature − measured liquid line temperature = 125 − 122 = 3°F.

D: A medium-pressure refrigerant; a field-built system using it needs Type II. By its saturation pressure at 104°F, R-500 is medium-pressure (low below 45 psia, medium 45 to 170, high 170 to 355, very high above 355). Low-pressure equipment is Type III; medium-, high- and very high-pressure equipment is Type II.

A: 15 inches of mercury vacuum. R-134a is a medium-pressure refrigerant. For a medium-pressure appliance with 200 pounds or more, recovered with equipment made on or after November 15, 1993, table 1 of 40 CFR 82.156 requires 15 inches of mercury vacuum.

1. R-134a: medium pressure.
2. Charge: 250 lb, so 200 pounds or more.
3. Equipment after November 15, 1993: 15 inches.

The trap: Using 10 inches, the figure for under 200 pounds.

A: 14°F. Subcooling is how far the liquid has been cooled below its condensing (saturation) temperature: 112 − 98 = 14°F.

1. Subcooling = saturation temperature − liquid line temperature.
2. 112 − 98 = 14.
3. So 14°F of subcooling.

The trap: Subtracting the other way round, or confusing it with superheat, which is measured on the suction side.

A: 50% per year; yes, it is over the 20% threshold. Using the annualizing method: (pounds added ÷ full charge) × (365 ÷ days since the last charge) × 100 = (30 ÷ 120) × (365 ÷ about 182) × 100 ≈ 50% per year. Commercial refrigeration with 50 pounds or more must be repaired above 20%.

1. Share of the charge: 30 ÷ 120 = 25% in about half a year.
2. Projected over a year: about 50%.
3. Commercial refrigeration threshold: 20%. 50% is over, so repair.

The trap: Forgetting to project to a full year (25%). The leak rate is per year.

C: 15 psig. Low-pressure chillers are not built for high pressure. The rupture disc opens at 15 psig to protect the vessel.

The trap: Choosing a high-pressure figure. Low-pressure chillers are built for low pressures, so the disc opens at 15 psig.

D: About 12.7 psia. 4 in Hg × 0.491 = 1.96 psi below atmospheric. 14.7 − 1.96 ≈ 12.7 psia.

A: 10 psig. The rupture disc on a low-pressure chiller opens at 15 psig, so leak testing raises the pressure to no more than 10 psig, usually with controlled hot water or heating blankets (or a pressurizing kit).

1. Rupture disc setting: 15 psig.
2. Stay below it with a margin.
3. So no more than 10 psig.

The trap: Choosing 15 psig. That is where the disc bursts, not a safe test pressure.

A: It removes most of the charge quickly before vapor recovery. Most of a chiller's charge is liquid, and liquid moves far faster than vapor. Recovering liquid first, then vapor down to the required level, saves hours, and water is kept circulating in the tubes to stop them freezing as the pressure drops.

1. Most of the charge is liquid.
2. Liquid transfers much faster than vapor.
3. So recover liquid first, then vapor.

The trap: Thinking the order is about safety of the purge unit. It is about speed.