EPA 609 MVAC System Components & Operation 3

Question 1

What does 'superheat' refer to in MVAC system diagnostics?

Accepted Answer

The temperature of refrigerant vapor above its boiling point at a given pressure

Answer

The temperature of the compressor oil

Answer

The temperature difference between ambient air and cabin air

Answer

The heat generated by the compressor clutch

Question 2

What does 'subcooling' measure in an MVAC system?

Accepted Answer

How much the liquid refrigerant is cooled below its condensing temperature at high-side pressure

Answer

How far below freezing the evaporator gets

Answer

The temperature of the air entering the evaporator

Answer

The amount of refrigerant in vapor form

Question 3

What component prevents compressor damage by shutting off the system when pressure is too low or too high?

Accepted Answer

Pressure switches (low-pressure and high-pressure cutout switches)

Answer

The TXV (Thermal Expansion Valve)

Answer

The receiver-drier

Answer

The orifice tube

Question 4

When retrofitting an R-12 system to R-134a, which component should always be replaced?

Accepted Answer

The receiver-drier or accumulator

Answer

The compressor

Answer

The condenser

Answer

The evaporator

Question 5

What is the purpose of an MVAC system accumulator (used with orifice tube systems)?

Accepted Answer

To store excess liquid refrigerant and separate liquid from vapor on the low side

Answer

To filter the refrigerant and oil mixture on the high side

Answer

To pressurize refrigerant before it enters the condenser

Answer

To measure superheat automatically

Question 6

What is indicated when an MVAC compressor cycles on and off rapidly (short cycling)?

Accepted Answer

Low refrigerant charge triggering the low-pressure cutout switch

Answer

Normal operation in cold weather

Answer

Condenser fan running too fast

Answer

The system is in economy mode