GM GM HVAC and Climate Control 2 — Questions and Answers
Question 1: What DTC would typically indicate a faulty blend door actuator on a GM vehicle?
- P0128
- B0223 or similar B-code related to the HVAC actuator position (Correct answer)
- C0035
- U0100
Correct answer: B0223 or similar B-code related to the HVAC actuator position
Blend door actuator faults are reported as B-prefix body DTCs (e.g., B0223) related to the HVAC temperature door position sensor or motor circuit.
Question 2: How should a GM technician verify the correct refrigerant charge after an AC system recharge?
- By feel — if air from vents is cold, charge is correct
- By measuring high and low side pressures and comparing to temperature-pressure charts (Correct answer)
- By weighing the refrigerant can before and after
- By checking only the sight glass on the receiver-drier
Correct answer: By measuring high and low side pressures and comparing to temperature-pressure charts
Proper charge verification requires measuring both high and low side pressures with a manifold gauge set and comparing readings to the temperature-pressure chart for the specific refrigerant.
Question 3: What is the function of the GM HVAC system's recirculation mode?
- Draws fresh outside air into the cabin
- Recirculates cabin air to improve cooling efficiency and block outside odors (Correct answer)
- Activates the rear window defroster
- Switches to maximum heat output
Correct answer: Recirculates cabin air to improve cooling efficiency and block outside odors
Recirculation mode closes the outside air inlet and recirculates interior cabin air, which is already cooled and allows the AC to reach target temperature faster while blocking outside odors.
Question 4: A GM vehicle's automatic climate control is not responding to temperature inputs. The blower operates normally. Which component should be diagnosed first?
- The blower motor resistor
- The HVAC control module and blend door actuators (Correct answer)
- The evaporator temperature sensor
- The AC compressor clutch relay
Correct answer: The HVAC control module and blend door actuators
When blower function is normal but temperature control is unresponsive, the HVAC control module and blend door actuators should be diagnosed as they govern temperature door positioning.
Question 5: Which GM component cycles the AC compressor on and off to prevent evaporator freeze-up on systems without an expansion valve?
- Thermal expansion valve (TXV)
- Pressure cycling switch (Correct answer)
- Accumulator desiccant pack
- Condenser pressure relief valve
Correct answer: Pressure cycling switch
The pressure cycling switch monitors low-side pressure and cycles the compressor off when pressure drops too low (indicating near-freeze conditions) to prevent evaporator icing.
Question 6: What precaution is required when handling R-1234yf refrigerant that is NOT required for R-134a?
- R-1234yf requires no special precautions beyond R-134a
- R-1234yf is mildly flammable and requires use of dedicated non-sparking equipment and proper ventilation (Correct answer)
- R-1234yf must be stored at sub-zero temperatures at all times
- R-1234yf reacts violently with water and must be kept completely dry
Correct answer: R-1234yf is mildly flammable and requires use of dedicated non-sparking equipment and proper ventilation
R-1234yf is classified as mildly flammable (A2L), requiring dedicated recovery/recharge equipment that is approved for flammable refrigerants and adequate ventilation during service.
GM GM HVAC and Climate Control 2
What DTC would typically indicate a faulty blend door actuator on a GM vehicle?