310T HVAC and Cab Systems Questions and Answers

Question 1

A technician connects a manifold gauge set to a truck's A/C system and finds the static pressure (engine off) is 30 PSI on both high and low sides, with an ambient temperature of 25°C (77°F).
When the A/C is turned on, the compressor clutch does not engage.
What is the most likely cause?

Accepted Answer

A significant refrigerant leak.

Answer

A faulty compressor clutch relay.

Answer

An overcharged refrigerant system.

Answer

A clogged thermal expansion valve (TXV).

Question 2

Which of the following is a key characteristic of R-1234yf refrigerant compared to the older R-134a refrigerant?

Accepted Answer

It is classified as mildly flammable and requires specific service equipment.

Answer

It has a significantly higher Global Warming Potential (GWP).

Answer

It is a direct drop-in replacement for R-134a systems without modification.

Answer

It operates at much higher pressures than R-134a.

Question 3

A driver complains of no heat from the vents. The technician confirms the engine reaches normal operating temperature and the blower motor functions correctly on all speeds. Which of the following is the LEAST likely cause of this problem?

Accepted Answer

A faulty blower motor resistor.

Answer

A heater control valve that is stuck closed.

Answer

A blend door actuator that has failed in the cold position.

Answer

A completely clogged heater core.

Question 4

What is the primary function of a receiver/drier in a commercial vehicle A/C system equipped with a thermal expansion valve (TXV)?

Accepted Answer

To store liquid refrigerant and remove moisture using a desiccant.

Answer

To meter refrigerant into the evaporator based on heat load.

Answer

To protect the compressor from liquid refrigerant slugging.

Answer

To cycle the compressor on and off based on system pressure.

Question 5

A driver reports a persistent whistling noise coming from the top of the passenger-side window at highway speeds. The window appears to be fully closed. Which of the following is the most effective and logical first diagnostic step?

Accepted Answer

Apply masking tape over the exterior window and door seals, then road test.

Answer

Immediately replace the door's weatherstripping.

Answer

Use a smoke machine to pressurize the cab and look for leaks.

Answer

Disassemble the door panel to inspect the window regulator alignment.

A technician connects a manifold gauge set to a truck's A/C system and finds the static pressure (engine off) is 30 PSI on both high and low sides, with an ambient temperature of 25°C (77°F).When the A/C is turned on, the compressor clutch does not engage.What is the most likely cause?

A technician connects a manifold gauge set to a truck's A/C system and finds the static pressure (engine off) is 30 PSI on both high and low sides, with an ambient temperature of 25°C (77°F).
When the A/C is turned on, the compressor clutch does not engage.
What is the most likely cause?