310T HVAC and Cab Systems 3

Question 1

A truck's cab heater produces warm air only at idle but blows cool air at highway speeds. What is the most likely cause?

Accepted Answer

Low coolant level causing air pockets at higher RPM

Answer

Faulty blower motor resistor

Answer

Clogged cabin air filter

Answer

Defective compressor clutch

Question 2

When recovering refrigerant from a 310T-compliant truck A/C system, the technician must:

Accepted Answer

Use EPA-certified recovery equipment and store refrigerant in approved containers

Answer

Vent the refrigerant outside the shop

Answer

Mix recovered refrigerant with new refrigerant before reuse

Answer

Only recover refrigerant if the system pressure exceeds 200 psi

Question 3

A coach A/C system uses a thermostatic expansion valve (TXV). The evaporator is frosting over. What is the most probable cause?

Accepted Answer

TXV stuck closed restricting refrigerant flow

Answer

Overcharged system

Answer

Condenser fan running too fast

Answer

High ambient temperature

Question 4

What does a sight glass with bubbles during A/C system operation typically indicate?

Accepted Answer

The system is low on refrigerant

Answer

The system is fully charged

Answer

The compressor is overloaded

Answer

The condenser is blocked

Question 5

A truck cab blower motor runs only on high speed. Which component is most likely faulty?

Accepted Answer

Blower motor resistor or speed control module

Answer

Blower motor itself

Answer

HVAC control head

Answer

Evaporator temperature sensor

Question 6

On a coach with dual-zone HVAC, the rear zone blows warm air while the front zone cools correctly. What should the technician check first?

Accepted Answer

Rear zone blend door actuator and control valve

Answer

Compressor output pressure

Answer

Refrigerant charge level

Answer

Condenser coil cleanliness

Question 7

What is the purpose of a receiver-drier in a truck A/C system?

Accepted Answer

To store liquid refrigerant and remove moisture and contaminants

Answer

To increase refrigerant pressure before the compressor

Answer

To regulate evaporator pressure

Answer

To cool refrigerant after it leaves the condenser