Heating, Ventilation and Air Conditioning (HVAC) Flashcards

What refrigerant replaced R-12 (Freon) in automotive A/C systems to reduce ozone depletion?

Answer: R-134a

R-134a replaced R-12 due to its significantly lower ozone depletion potential, becoming mandatory in North American vehicles after 1995.

What is the primary function of the receiver-drier in an automotive A/C system?

Answer: To remove moisture and filter contaminants from the refrigerant

The receiver-drier stores liquid refrigerant, removes moisture using a desiccant, and filters contaminants from the high-pressure liquid line.

In an A/C system using a fixed orifice tube, which component stores refrigerant and separates liquid from vapour on the low side?

Answer: Accumulator

The accumulator is located on the low-pressure side between the evaporator and compressor, storing excess refrigerant and preventing liquid slugging at the compressor.

In what physical state does refrigerant enter the evaporator during normal A/C system operation?

Answer: Low-pressure liquid/vapour mixture

After passing through the expansion device, refrigerant enters the evaporator as a low-pressure liquid/vapour mixture, absorbing heat from cabin air as it evaporates.

What is the primary function of the condenser in an automotive A/C system?

Answer: To release heat from the refrigerant to the outside air

The condenser removes heat from high-pressure refrigerant vapour, causing it to condense into a liquid as outside air flows through its fins.

In a TXV-type A/C system, what does the sensing bulb on the thermostatic expansion valve monitor?

Answer: Evaporator outlet temperature and pressure

The TXV sensing bulb monitors evaporator outlet temperature and pressure to regulate refrigerant flow, maintaining optimal evaporator superheat.

What is the typical low-side (suction) pressure range for a properly charged R-134a system at approximately 25°C ambient temperature?

Answer: 138–207 kPa (20–30 psi)

A properly charged R-134a system typically shows low-side pressures of 138–207 kPa (20–30 psi) at 25°C ambient, corresponding to evaporator temperatures just above 0°C.