NAPA Heating and Air Conditioning 2

Question 1

With the A/C running, gauges show low-side pressure higher than normal and high-side pressure lower than normal. What is the most likely cause?

Accepted Answer

Worn or failing compressor

Answer

A compressor with internal leakage can't build head pressure, so the low side reads high and the high side reads low.

Question 2

Both low-side and high-side pressures read higher than specification, and the condenser fan is working. What should be checked next?

Accepted Answer

Refrigerant overcharge or debris blocking the condenser fins

Answer

Too much refrigerant or poor heat rejection at the condenser raises pressure on both sides.

Question 3

On an orifice tube system, frost forms on the liquid line just ahead of the orifice tube and both pressures are low. What is indicated?

Accepted Answer

Restricted orifice tube

Answer

A restriction causes a pressure drop and cooling at the blockage point, producing frost there.

Question 4

A system cools well for a while, then blows warm air, then cools again after being shut off. What is the most likely cause?

Accepted Answer

Moisture in the system freezing at the metering device

Answer

Moisture freezes at the expansion valve or orifice and blocks flow, then thaws when the system is off.

Question 5

Before connecting a recovery machine to a vehicle with unknown refrigerant history, what should the technician do first?

Accepted Answer

Use a refrigerant identifier to check purity

Answer

An identifier prevents contaminated or mixed refrigerant from entering and ruining the shop's recovery equipment and supply.

NAPA - National Automotive Parts Association Certified Mechanic Practice Test