Heating, ventilation and air conditioning is 4 of the 55 scored G1 questions (7%), from seven tasks. It's the A/C service visit: check how the system works, identify the refrigerant, recover and recharge, look for leaks, and the cabin filter and drains.
Verify HVAC operation: vent temperature, blower and condenser fan, compressor engagement, blend and mode doors (G.1).
Identify the A/C refrigerant type; recover and recharge to the manufacturer's specifications (G.2).
Check A/C components visually for signs of leaks (G.3).
Inspect the condenser for restricted airflow (G.4).
Inspect and replace the cabin air filter (G.5).
Check the drive belt for wear and tension; adjust or replace (G.6).
Inspect and clean the evaporator drains (G.7).
HVAC questions
0 of 12 answered · 0 correct
Question 1 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
A vehicle has poor heater performance. The cooling system is full and has been bled of air. With the engine at normal operating temperature, a technician measures the heater hoses at the firewall. The inlet (supply) heater hose temperature is 195°F and the outlet (return) heater hose temperature is 105°F. Which of the following is the most likely cause?
Explanation
Incorrect: A failed water pump impeller lowers flow everywhere and would cause overheating, while the engine here runs at normal temperature.
Incorrect: A stuck blend door changes air mixing inside the case; coolant would still flow and both hoses would be hot.
Incorrect: A clogged cabin air filter cuts airflow, but it does not create a large temperature drop across the heater hoses.
Incorrect: A thermostat stuck open keeps coolant cool, so the inlet hose would not read 195°F.
Correct: A 90°F drop across the heater core means little coolant is flowing through it; a restricted (plugged) core gives a hot inlet and a much cooler outlet.
Question 2 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
A customer complains of weak airflow from the dashboard vents and persistent window fogging during rain. The blower motor is audible and changes speed correctly when commanded. What should be checked first?
Explanation
Incorrect: The blower changes speed correctly, so the blower resistor is working.
Incorrect: Evacuating and recharging the system affects air temperature, not the volume of air from the vents.
Incorrect: A blend door actuator controls the temperature mix; it does not reduce total airflow.
Incorrect: Replacing the heater core is a major job and is not suggested by weak airflow with a normal blower.
Correct: The blower runs at every speed, so weak airflow points to a restriction; a clogged cabin air filter also holds moisture and adds to window fogging.
Question 3 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
A customer complains of poor airflow from the vents. The technician replaces a heavily soiled cabin air filter, but the airflow at the vents remains lower than specified. Which action should be performed next?
Explanation
Incorrect: A failed resistor block shows up as missing fan speeds, not as weak airflow on every speed.
Incorrect: Blend door actuators set the temperature mix and do not limit the total volume of air.
Incorrect: Evacuating and recharging the A/C system affects how cold the air is, not how much air comes out.
Correct: With a new filter and still-low airflow, the next checks are the blower motor's speed and draw and the ducting and intake for blockages such as leaves or a loose duct.
Incorrect: Replacing the control head is guessing when the blower runs and responds to commands.
Question 4 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
An A/C system is found to have 15 psi on the low side and 75 psi on the high side while the compressor is engaged. Which procedure should be performed before opening the system for repair?
Explanation
Incorrect: Fluorescent dye helps find a leak but does not prepare the system to be opened.
Correct: Before any A/C component is opened, the refrigerant left in the system is recovered with certified equipment; venting it is illegal.
Incorrect: Service port valves are replaced only after recovery; doing it first releases refrigerant.
Incorrect: Venting refrigerant to the atmosphere is prohibited under the Clean Air Act.
Incorrect: Charging to specification just before the system is opened wastes refrigerant and releases it during the repair.
Question 5 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
Technician A says that an A/C system should be charged by weight to the manufacturer's specified mass. Technician B says that charging until the pressures look correct on the manifold gauge set is the preferred method. Who is correct?
Explanation
Correct: Technician A is right: manufacturers specify the A/C charge by weight, and charging by weight with a scale or machine is the accurate method.
Incorrect: Technician B is wrong: pressures depend on temperature, humidity and airflow, so charging to 'correct-looking' pressures is not reliable.
Incorrect: Charging by pressure is not the preferred method, so both cannot be correct.
Incorrect: Technician A describes the specified method, so rejecting both is wrong.
Question 6 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
The A/C compressor clutch does not engage on a vehicle with an R-134a system. The ambient temperature is 80°F (27°C). The static pressure on both the high and low sides reads 45 psi (310 kPa). What does this pressure reading indicate?
Explanation
Incorrect: A fully charged system would read near 87 psi at 80°F, not 45 psi.
Incorrect: Condenser airflow matters only while the system runs; it does not change static pressure.
Correct: Static pressure with liquid refrigerant present matches the saturation pressure, about 87 psi for R-134a at 80°F; 45 psi means little liquid is left, and the low-pressure switch keeps the clutch off.
Incorrect: With the engine off both sides equalize, so a stuck expansion valve cannot cause a low static reading.
Incorrect: A failed clutch coil stops engagement, but it does not lower static pressure; 45 psi itself points to a low charge.
Question 7 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
An A/C system cools poorly at idle with recirculation mode selected. Diagnostics show the air intake temperature at the evaporator is 85°F while the cabin temperature is 70°F. What is the likely cause of this condition?
Explanation
Correct: Air entering the evaporator at 85°F while the cabin is 70°F means outside air is coming in, so the recirculation door is not closing.
Incorrect: A leaking heater control valve warms air after the evaporator; it does not raise the intake air temperature.
Incorrect: An expansion valve stuck open changes evaporator pressure and cooling, not the temperature of air entering the evaporator.
Incorrect: A faulty evaporator temperature sensor misreads the core but does not let outside air in.
Incorrect: The mode door picks the outlets (dash, floor, defrost); it does not choose between fresh and recirculated air.
Question 8 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
During a routine multipoint inspection, a technician removes the cabin air filter and observes significant black mold growing on the filter pleats. Which of the following is the correct service action to take?
Explanation
Incorrect: A fungicidal spray does not remove mold from the media; the filter is a disposable part.
Incorrect: Shaking out debris leaves the mold in place and puts it back in the air supply.
Correct: A moldy cabin filter cannot be cleaned; it is replaced, and the evaporator and drain are checked for the moisture source.
Incorrect: Blowing the filter out with air spreads mold spores and leaves the growth in the pleats.
Incorrect: Washing with soap and water ruins the filter media, and a damp filter grows more mold.
Question 9 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
While servicing an automotive A/C system, a high-pressure line fitting suddenly disconnects, rapidly releasing a large cloud of refrigerant into the work area. What is the first thing the technician should do?
Explanation
Incorrect: Reaching in to close a valve exposes the technician to liquid refrigerant at very low temperature.
Incorrect: Reaching in to turn off the engine puts the technician in the refrigerant cloud; getting clear comes first.
Incorrect: A rag over the leak puts the hand in the spray and does not stop the release.
Correct: Escaping refrigerant can cause frostbite and displaces oxygen in an enclosed bay, so the technician first steps back and lets the area ventilate.
Incorrect: Reaching into the spray to reconnect the line risks frostbite to hands and eyes.
Question 10 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
A vehicle arrives for A/C service. Before connecting the recovery machine to the service ports, what is the mandatory first step to prevent equipment contamination?
Explanation
Incorrect: Vent temperature checks performance, not what refrigerant is in the system.
Correct: A refrigerant identifier confirms the type and purity before connection, so a contaminated or wrong refrigerant never enters the recovery machine.
Incorrect: Compressor oil is checked during component service, not before connecting the recovery machine.
Incorrect: Ambient humidity matters for reading performance charts, not for protecting the recovery equipment.
Incorrect: Static pressure does not reveal contamination or a mixed refrigerant.
Question 11 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
During an inspection, a cabin air filter is found to be saturated with moisture and clogged with heavy debris. A strong musty odor is present in the vehicle interior. Which service action is recommended?
Explanation
Incorrect: A new cabin filter alone leaves the mold on the evaporator, so the odor returns.
Incorrect: Deodorizer on the cowl intake does not reach the evaporator where the smell starts.
Incorrect: Blowing out a wet, moldy filter spreads spores and puts the same filter back.
Incorrect: A charcoal cabin filter masks odor but leaves the moldy evaporator untreated.
Correct: A wet, clogged filter with a musty smell means mold is growing on the evaporator too; the core is cleaned (and its drain checked) and the filter replaced.
Question 12 of 12 · Heating, Ventilation, and Air Conditioning · 7%Not answered
A technician observes higher-than-normal pressure readings on both the high and low sides of an A/C system. The compressor clutch is engaged, and the refrigerant charge has been verified by weight. Which area should be checked for obstruction?
Explanation
Incorrect: A blocked expansion valve starves the evaporator, which drops low-side pressure instead of raising it.
Correct: With the charge correct, high pressure on both sides means the condenser cannot shed heat; debris on its fins or a weak fan blocks the airflow across it.
Incorrect: An iced evaporator core restricts airflow and pulls low-side pressure down, not up.
Incorrect: A wide compressor clutch air gap makes the clutch slip or not engage, and the clutch is engaged here.
Incorrect: A cabin temperature sensor affects automatic climate control, not system pressures.
Answer every question to see your score
Identify before you connect
Task G.2 starts with identifying the refrigerant, and that comes before recovery. R-134a and R-1234yf systems use different service fittings and need separate equipment, and a contaminated or mixed charge shouldn't go into a recovery machine. The charge amount is set by weight on the under-hood label, so a recharge goes by the scale, not by gauge pressures alone.
Where A/C work becomes an A-test
Diagnosing compressor, control and temperature faults is the A7 Heating and Air Conditioning test, which this site doesn't cover yet. Separately, servicing vehicle A/C for pay in the US requires EPA Section 609 technician certification, which G1 does not replace (EPA).