EPA 609 MVAC System Components & Operation 5

Question 1

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

Accepted Answer

In the liquid line, usually at the evaporator inlet

Answer

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.

Question 2

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

Accepted Answer

Low-pressure vapor

Answer

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

Question 3

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

Accepted Answer

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

Answer

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

Question 4

Moisture left in an MVAC system can cause which problem?

Accepted Answer

Ice at the metering device and acid that corrodes components

Answer

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

Question 5

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

Accepted Answer

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

Answer

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

EPA 609 - EPA Section 609 Refrigerant Certification Practice Test