ASE G1 heating and air conditioning practice questions.

Five free practice questions on heating and air conditioning: content area G of the ASE G1 Auto Maintenance & Light Repair test, 4 of its 55 scored questions (7.3%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Recall · Heating, Ventilation, and Air Conditioning

   With the engine running and the A/C turned on, which of these confirms that a compressor's electromagnetic clutch has engaged?

   1. The low-side pressure rises above static
   2. The pulley turns whenever the engine runs
   3. The idle speed rises as A/C is selected
   4. The clutch hub turns with the pulley
   Show the answer

   D. Correct. The pulley spins on its own bearing whenever the belt turns; only when the coil is energized is the hub (armature plate) pulled against the pulley, so a hub turning with the pulley proves engagement. A hub that stays still with the coil powered points to the coil or the clutch air gap.

   Why not the others

   A. When the compressor pumps, it pulls the low side down below the static pressure, not above it. A low side that stays at static suggests the compressor is not running; the hub turning with the pulley is the direct check.

   B. The pulley is driven by the belt and spins on its bearing whether the clutch is engaged or not. Only the hub, which is splined to the compressor shaft, shows that the compressor itself is being driven.

   C. Many PCMs raise idle as soon as they receive the A/C request, which can happen even if the clutch never pulls in. Watch the clutch hub for proof of engagement.

2. Recall · Heating, Ventilation, and Air Conditioning

   On an orifice-tube A/C system with a cycling clutch, the compressor clutch engages and releases every so often on a mild day while the vent air stays cold. What is this cycling for?

   1. To keep the evaporator from icing up
   2. To hold high-side pressure below its limit
   3. To cut compressor load on hard acceleration
   4. To let oil drain back to the compressor
   Show the answer

   A. Correct. The cycling switch senses low-side pressure, which tracks evaporator temperature (some systems sense the core temperature directly), and opens the clutch circuit before the core gets cold enough to freeze its condensate. Ice on the fins would block airflow, so steady cycling with cold vent air on a mild day is normal operation, not a fault.

   Why not the others

   B. Limiting high-side pressure is the job of the high-pressure cutout switch, which opens only when pressure climbs abnormally high, as with poor condenser airflow. Routine cycling with cold vent air comes from the low-side cycling switch protecting the evaporator from icing.

   C. Cutting the compressor on hard acceleration is a separate PCM strategy and happens only at heavy throttle. Regular cycling while cruising or idling with cold vent air is the cycling switch keeping the evaporator above freezing.

   D. Oil travels around the system with the refrigerant while the compressor runs; the clutch is not cycled to return it. The cycling keeps the evaporator from freezing its condensate.

3. Recall · Heating, Ventilation, and Air Conditioning

   A technician tries to connect the couplers of an R-134a recovery/recycling/recharging machine to a vehicle charged with R-1234yf, and they will not fit its service ports. Why?

   1. R-1234yf ports are sized for higher pressures
   2. R-1234yf systems must have unique fittings
   3. The R-134a couplers need an R-1234yf adapter
   4. R-1234yf ports are on the high side only
   Show the answer

   B. Correct. Federal rules allow R-1234yf in new cars and light trucks only with the SAE J639 safety requirements, which include unique service fittings, so an R-134a coupler cannot connect and mix the two refrigerants in the system or the machine. The vehicle is serviced with a machine certified for R-1234yf (SAE J2843) or for both refrigerants (SAE J3030).

   Why not the others

   A. R-1234yf operates at pressures within a few psi of R-134a's at the same temperature, so pressure is not why the ports differ. The fittings differ by design so equipment for one refrigerant cannot be connected to the other.

   C. No adapter makes an R-134a machine right for this vehicle: R-1234yf must be recovered, recycled and recharged with equipment certified for it, and an adapted R-134a machine would mix the two refrigerants. The ports are made unique so that cannot happen.

   D. R-1234yf systems have both a high-side and a low-side service port. The couplers fit neither because R-1234yf systems carry their own unique fittings, unlike R-134a's.

4. Recall · Heating, Ventilation, and Air Conditioning

   During a visual check of an A/C system, the technician finds an oily, dirt-caked film around one hose crimp. Why does this suggest a refrigerant leak at that spot?

   1. Condensation on the cold crimp traps road dust
   2. Escaping refrigerant condenses into an oily liquid
   3. Escaping refrigerant carries oil out with it
   4. Leak detection dye turns oily when exposed to air
   Show the answer

   C. Correct. Compressor oil circulates with the refrigerant, so wherever refrigerant seeps out, oil comes with it and stays behind after the refrigerant evaporates; road dirt then sticks to it. Confirm the spot with an electronic leak detector or dye before replacing the hose.

   Why not the others

   A. Water that condenses on a cold line dries off and leaves no oily film. The oil is the system's own lubricant, carried out by refrigerant escaping at that crimp.

   B. Refrigerant escaping to the atmosphere boils off into a vapor; it does not stay behind as an oily liquid. The film is the system's lubricating oil, which the escaping refrigerant carries out with it.

   D. Dye rides in the system oil and glows under an ultraviolet lamp, but it does not turn into an oily film by itself, and many systems have no dye added. The film is the system's oil left behind by escaping refrigerant.

5. EXCEPT · Heating, Ventilation, and Air Conditioning

   Any of these can reduce the airflow through an A/C condenser EXCEPT:

   1. leaves packed between the condenser and the radiator.
   2. condenser fins flattened by road debris.
   3. an electric cooling fan that does not run.
   4. a partly restricted orifice tube.
   Show the answer

   D. Correct. An orifice tube restricts the refrigerant flowing inside the system, not the air moving across the condenser's fins, so it shows up as abnormal pressures and poor cooling rather than less airflow. The other three all block or weaken the air the condenser needs to shed heat.

   Why not the others

   A. Debris trapped between the condenser and the radiator blocks air through both cores and is often hidden from the front, so it is checked by looking between the cores with a light. It can reduce condenser airflow.

   B. Fins bent flat close the air passages between the tubes, so less air crosses the condenser. Lightly bent fins can be straightened with a fin comb.

   C. At idle and low speed there is little ram air, so the condenser depends on the fan to pull air through it. A fan that does not run leaves the condenser short of air, and cooling suffers most in traffic.

02Answer key

03What area G covers

This content area covers the HVAC checks and services done in maintenance and light repair: verifying vent temperature, blower, condenser fan, compressor clutch and door operation, identifying the refrigerant, recovering and recharging to the manufacturer's specifications, looking for signs of leaks, checking condenser airflow, and servicing cabin air filters, compressor belts and evaporator drains.

The ASE test specification calls this content area “Heating, Ventilation, and Air Conditioning”. It carries 4 of the 55 scored questions, 7.3% of the test.

• Check vent temperature, blower, fan and clutch operation
• Check blend and mode door operation
• Identify refrigerant before recovery
• Recover and recharge to the label weight
• Look for oily residue and other leak signs
• Check condenser airflow and cabin air filters
• Inspect compressor belts and clear evaporator drains

04What the questions turn on

Cold suction line, warm vents

When the compressor runs and the suction line is cold but the vents blow warm at full cold, the refrigerant side is working. A blend door stuck at full heat reheats the chilled air, and moving the temperature control changes nothing.

Identify before you recover

A refrigerant identifier samples the system and reports whether it holds pure R-134a or R-1234yf or is contaminated. Checking before the recovery machine is connected keeps the machine and its stored refrigerant from being contaminated.

Charge by weight after a vacuum

After recovery and evacuation the system is empty, so the full label weight goes back in, charged by weight. A vacuum that rises during the hold means air leaking in or moisture boiling off, and that is fixed before charging.

Water on the passenger floor

Clear, odorless water on the passenger floor after humid weather with the A/C in use points to a plugged evaporator drain. The condensate that should drip out under the car overflows the case into the cabin instead.

05The other content areas

The G1 test has seven content areas. Each has its own page of free questions:

The ASE G1 Auto Maintenance & Light Repair practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.

ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.