310T HVAC and Cab Systems 4

Question 1

A 310T technician measures A/C high-side pressure of 350 psi and low-side pressure of 55 psi on a hot day. What does this indicate?

Accepted Answer

Overcharged system or condenser airflow restriction

Answer

Abnormally high high-side pressure with elevated low-side suggests excess refrigerant or heat not being dissipated, often from a blocked or dirty condenser.

Question 2

Which refrigerant is currently approved for use in heavy-duty truck and coach A/C systems in the United States?

Accepted Answer

R-134a or HFO-1234yf depending on system design

Answer

R-134a has been the standard for heavy-duty mobile A/C, with HFO-1234yf being adopted in newer systems as regulations tighten on global warming potential.

Question 3

During cab pressurization testing on a coach, excessive cab pressure drop indicates:

Accepted Answer

Air leaks in door seals, windows, or cab penetrations

Answer

Rapid pressure loss during a cab pressurization test points to unsealed gaps where pressurized air escapes, compromising dust and noise isolation.

Question 4

What causes a compressor to short-cycle (turn on and off rapidly) in a truck A/C system?

Accepted Answer

Low refrigerant charge causing the low-pressure cutout switch to trip repeatedly

Answer

Low refrigerant causes suction pressure to drop below the low-pressure switch threshold, cycling the compressor off; when pressure recovers slightly, it cycles on again.

Question 5

A technician finds oil residue around an A/C hose fitting on a truck. This most likely indicates:

Accepted Answer

A refrigerant leak at that fitting, since refrigerant oil escapes with refrigerant

Answer

Refrigerant carries compressor oil with it; oil residue at a joint is a reliable indicator of a refrigerant leak at that location.

(310t) Truck and Coach Technician Certification Practice Test

(310t) Truck and Coach Technician Certification Practice Test

310T HVAC and Cab Systems 4