HVAC Troubleshooting 3

Question 1

A technician finds high suction pressure and high discharge pressure with low superheat on an R-410A system. What is the most likely problem?

Accepted Answer

Refrigerant overcharge

Answer

Both elevated suction and discharge pressures combined with low superheat are classic signs of an overcharged refrigerant system.

Question 2

An oil furnace fails to fire and the reset button on the primary control trips repeatedly. What should be checked first?

Accepted Answer

Fuel supply and oil filter condition

Answer

A clogged oil filter or empty fuel tank is the most common reason for repeated primary control lockout, as the burner cannot establish flame without adequate fuel.

Question 3

A packaged rooftop unit produces insufficient cooling. Subcooling is 5°F and superheat is 18°F. What does this suggest?

Accepted Answer

Refrigerant undercharge

Answer

Low subcooling combined with elevated superheat indicates a refrigerant undercharge, reducing system capacity and efficiency.

Question 4

A gas furnace produces a yellow, flickering flame. What is the most common cause?

Accepted Answer

Insufficient primary air to the burner

Answer

Insufficient primary air mixing with gas causes incomplete combustion, producing a yellow, sooty, or flickering flame instead of a clean blue flame.

Question 5

After replacing a compressor, the system has high head pressure and high amp draw. The technician suspects what?

Accepted Answer

Non-condensables (air) in the system

Answer

Non-condensable gases like air raise head pressure significantly because they cannot condense, adding to the pressure burden on the compressor.

HVAC Practice Test

HVAC Practice Test

HVAC Troubleshooting 3