GM HVAC and Climate Control Flashcards

What is the correct procedure when replacing a GM evaporator core regarding the receiver-drier or accumulator?

Answer: The receiver-drier/accumulator must also be replaced since the system is being opened

GM service procedures require replacing the receiver-drier or accumulator any time the system is opened, as the desiccant becomes saturated when exposed to atmospheric moisture.

On GM vehicles equipped with rear HVAC, where is the secondary expansion device typically located?

Answer: At the rear HVAC module under the rear cargo area or rear of the passenger compartment

The rear HVAC module contains its own expansion device (orifice tube or TXV) located within the rear heating/cooling unit, separate from the front system's expansion device.

A GM technician performs a leak test on an AC system using which preferred method per current GM service procedures?

Answer: Electronic refrigerant leak detector or UV dye with UV lamp

GM recommends using an electronic refrigerant leak detector or ultraviolet dye with a UV lamp to precisely locate leaks, as these methods can detect small leaks accurately.

What is the typical PAG oil specification concern when servicing a GM system that has been converted from R-134a to R-1234yf?

Answer: R-1234yf requires PAG oil with a specific viscosity grade approved for use with that refrigerant — do not mix with R-134a PAG oil

R-1234yf systems require PAG oil certified compatible with R-1234yf; using R-134a-grade PAG oil can cause compatibility issues and void warranty on system components.

When evacuating a GM AC system prior to recharging, what is the minimum vacuum level and hold time typically specified?

Answer: 500 microns or below, held for at least 15–30 minutes

GM service procedures typically require pulling the system down to 500 microns or less and holding that vacuum for a minimum of 15–30 minutes to ensure all moisture is boiled off before recharging.

A GM customer reports musty odor from the vents only when the AC first turns on. What is the most likely cause and recommended fix?

Answer: Microbial growth on the evaporator core — clean with approved HVAC disinfectant and replace cabin air filter

Musty odor on AC startup is caused by mold and bacteria growth on the damp evaporator core surface; the repair involves applying an approved HVAC disinfectant treatment and replacing the cabin air filter.