EPA 609 MVAC System Components & Operation 2 — Questions and Answers
Question 1: What does a typical MVAC manifold gauge set measure?
- Only high-side pressure
- Only low-side pressure
- Both high-side and low-side pressures simultaneously (Correct answer)
- Refrigerant purity and moisture content
Correct answer: Both high-side and low-side pressures simultaneously
A manifold gauge set has two gauges — a blue low-side gauge and a red high-side gauge — to simultaneously monitor both system pressures.
Question 2: What is a typical low-side pressure reading for a properly charged R-134a MVAC system at idle?
- 0–5 psi
- 25–45 psi (Correct answer)
- 100–150 psi
- 200–250 psi
Correct answer: 25–45 psi
A properly functioning R-134a system typically shows 25–45 psi on the low side at idle in normal ambient conditions.
Question 3: What is a typical high-side pressure reading for a properly charged R-134a MVAC system?
- 25–45 psi
- 50–100 psi
- 150–250 psi (Correct answer)
- 400–500 psi
Correct answer: 150–250 psi
The high side of an R-134a system typically operates between 150–250 psi depending on ambient temperature and load.
Question 4: What causes abnormally HIGH low-side pressure and HIGH high-side pressure in an MVAC system?
- Refrigerant undercharge
- Restriction in the high-side liquid line
- Overcharge or condenser cooling failure (Correct answer)
- Compressor clutch slipping
Correct answer: Overcharge or condenser cooling failure
Both pressures being high indicates an overcharged system or a condenser that cannot reject heat properly.
Question 5: Which service port connects to the LOW side of an MVAC system?
- The larger port (typically near the compressor inlet/accumulator) (Correct answer)
- The smaller port on the high side near the compressor outlet
- Either port — they are interchangeable
- The port on the condenser outlet
Correct answer: The larger port (typically near the compressor inlet/accumulator)
The low-side service port is larger and is located on the suction side of the compressor or near the accumulator.
Question 6: A sight glass showing bubbles in an R-134a system indicates:
- The system is fully charged and operating normally
- The system may be low on refrigerant (Correct answer)
- The system is overcharged
- The compressor is failing
Correct answer: The system may be low on refrigerant
Bubbles in the sight glass indicate that refrigerant is not fully liquid at that point, suggesting a low charge or restriction.
EPA 609 MVAC System Components & Operation 2
What does a typical MVAC manifold gauge set measure?