Applied Methods and Techniques Flashcards

A high-pressure appliance with 250 lb of HCFC-22 was made after November 15, 1993. What evacuation level is required before opening it?

Answer: 10 in. Hg vacuum

HCFC-22 appliances with 200 lb or more must be evacuated to 10 in. Hg with post-1993 equipment.

When recovering a large high-pressure system, why remove liquid refrigerant first?

Answer: Liquid recovery moves the most refrigerant fastest

Liquid is much denser than vapor, so removing it first cuts recovery time a lot.

What causes the refrigerant charge in a recovery cylinder to rise after a technician has stopped the recovery unit?

Answer: Liquid refrigerant left in the hoses or trapped in the unit draining into the cylinder

Liquid left in the hoses and unit can keep moving into the cylinder, which is why technicians watch the scale against the 80% limit.

Why must a technician wait a few minutes after reaching the required recovery vacuum on a high-pressure system?

Answer: To see if the pressure rises, which shows refrigerant is still trapped in the oil or system

A pressure rise means refrigerant is still coming out, so recovery should continue until the vacuum holds.

Which device on a high-pressure system can be damaged and stop working if a technician brazes near it without protection?

Answer: The pressure relief valve

Heat can damage relief valves and other heat-sensitive parts, so they must be protected or taken off before brazing.

Before charging a system that has been opened for repair, what must be done after the leak repair?

Answer: Pressure-test with nitrogen, then evacuate to remove air and moisture

A nitrogen pressure test confirms the repair, and evacuation removes the non-condensables and moisture that got in.

What is the main hazard of a high-pressure system filled with too much refrigerant during charging?

Answer: Excess head pressure and liquid slugging to the compressor

Overcharging raises discharge pressure and can send liquid back to the compressor, which damages it.