MVAC System Components & Operation Flashcards

In a typical R-134a orifice tube system, where is the fixed orifice tube usually found?

Answer: In the liquid line, usually at the evaporator inlet

The orifice tube is a fixed restriction in the liquid line, usually at or near the evaporator inlet, where high pressure drops to low pressure.

Under normal operation, what state should the refrigerant be in when it leaves the evaporator?

Answer: Low-pressure vapor

Refrigerant boils as it absorbs cabin heat in the evaporator, so it should leave as low-pressure vapor heading to the compressor.

Why do the high-side and low-side service ports on R-134a systems have different sizes?

Answer: So service hoses can't be connected to the wrong side

SAE-specified quick-connect fittings come in different sizes for each side so a technician can't hook a hose to the wrong port.

Moisture left in an MVAC system can cause which problem?

Answer: Ice at the metering device and acid that corrodes components

Water can freeze at the orifice tube or TXV and reacts with refrigerant and oil to form corrosive acids.

What is the purpose of the high-pressure relief valve found on many MVAC compressors?

Answer: To open and release pressure only if it reaches a dangerously high level

The relief valve is a last-resort device that opens at excessive pressure to keep components from rupturing, then reseats.

R-744 (CO2) MVAC systems use a gas cooler instead of a conventional condenser mainly because:

Answer: CO2 runs above its critical point on the high side, so it doesn't condense

R-744 operates transcritically at very high pressures, so heat is removed in a gas cooler without the refrigerant ever condensing to liquid.

What does a muffler installed in the compressor discharge line do?

Answer: Reduces pulsation noise from the compressor

The discharge muffler dampens pressure pulses from the compressor pistons so less noise reaches the cabin.