Applied Methods and Techniques Flashcards

During a standing vacuum test, the micron gauge reading rises after the pump is isolated and then levels off. What does this most likely indicate?

Answer: Moisture is still present in the system

A rise that levels off means moisture is boiling off until it reaches equilibrium, while a rise that keeps going points to a leak.

Which practice speeds up evacuation of a refrigeration system?

Answer: Using short, large-diameter hoses and removing Schrader valve cores

Short, wide hoses with the valve cores removed restrict flow less and pull a vacuum faster.

What is the safest way to pressurize a system for leak testing?

Answer: Dry nitrogen with a trace amount of HCFC-22

Dry nitrogen is inert and dry, and a trace of HCFC-22 lets an electronic detector find the leak.

A technician wants to speed up vapor recovery into a recovery cylinder. Which technique helps?

Answer: Cooling the recovery cylinder

A cooler cylinder has lower pressure, so the pressure difference that moves refrigerant into it is larger.

Why should zeotropic blends such as R-407C be charged into a system as a liquid?

Answer: To prevent fractionation, which changes the blend's composition

Zeotropic components boil at different temperatures, so vapor charging takes uneven amounts of each and changes the blend.

How do you check a recovery cylinder for non-condensable gases?

Answer: Let it reach ambient temperature, then compare its pressure with the refrigerant's saturation pressure at that temperature

If the cylinder pressure is above the saturation pressure for the ambient temperature, non-condensables are present.

Why would a technician heat a system during evacuation?

Answer: To raise the vapor pressure of trapped moisture so it boils off faster

Warming raises the vapor pressure of the water, so it evaporates and is pulled out more quickly.