Heating, Ventilation and Air Conditioning (HVAC) Flashcards

When diagnosing an A/C system with manifold gauges, what should be done FIRST to ensure accurate readings?

Answer: Run the engine and A/C system for 10 minutes to stabilize conditions

Running the engine and A/C for 10 minutes allows the system to reach stable operating conditions, ensuring accurate and comparable manifold gauge readings.

Both the high-side and low-side pressures are higher than normal specifications. This MOST likely indicates:

Answer: System overcharge or restricted condenser airflow

High pressures on both sides indicate the condenser cannot dissipate heat efficiently due to blocked airflow, damaged fins, or the system is overcharged with refrigerant.

Before opening an A/C system component for replacement, the technician MUST:

Answer: Recover the refrigerant using certified recovery equipment

Federal and provincial regulations require all refrigerant to be recovered using certified equipment before opening any A/C system component.

After replacing an A/C system component, what is the main purpose of evacuating the system with a vacuum pump?

Answer: To remove air and moisture from the system

Evacuation removes non-condensable air and moisture, which could cause corrosion, acid formation, and ice blockage in the expansion device.

What vacuum level should be achieved when evacuating an A/C system to ensure adequate moisture removal?

Answer: 500 microns (0.5 mm Hg) or lower

Pulling the system to 500 microns or below causes moisture to boil off at ambient temperature and be removed by the vacuum pump, preventing contamination.

An A/C compressor clutch that rapidly cycles on and off during operation is MOST likely caused by:

Answer: Low refrigerant charge activating the low-pressure protection switch

Low refrigerant charge causes low suction pressure, repeatedly triggering the low-pressure protection switch and causing rapid compressor clutch cycling.

What type of oil must be used when servicing an R-134a automotive A/C system compressor?

Answer: PAG (Polyalkylene Glycol) oil

PAG oil is required for R-134a compressors because it is miscible with R-134a and provides proper lubrication; mineral oil used with R-12 is not compatible.