Five ASE A7 Heating & Air Conditioning practice test questions, answers included.

1. Recall · Heating, Ventilation, A/C (HVAC), and Engine Cooling System Service, Diagnosis, and Repair

   On hot days, a customer hears a hiss from behind the dash for several seconds after the engine is shut off, but only when the A/C was running before shutdown. The A/C cools normally, and last week's recovery found the full label charge. What causes the hiss?

   1. Refrigerant escaping from a leak in the evaporator
   2. Pressures equalizing through the metering device
   3. Air rushing into the HVAC case as the blower stops
   4. Coolant percolating in the hot heater core
   Show the answer

   B. Correct. When the compressor stops, the high side is still at high pressure, and refrigerant keeps flowing through the expansion valve or orifice tube until both sides even out, which can be heard as a short hiss or gurgle behind the dash. A brief hiss like this is the system at work, not a leak; only an unusually loud or long noise calls for a check of the manufacturer's bulletins.

   Why not the others

   A. A leak loud enough to hear would empty a system quickly, and this one held its full charge; a leak would also hiss whenever the system holds pressure, not just after shutdown.

   C. The blower winds down quietly when the ignition is switched off, and air settling in the case does not make a hiss that lasts several seconds.

   D. Coolant noises follow the engine's heat, not A/C use; this hiss happens only when the A/C was running, which ties it to the refrigerant system.

2. Recall · Heating, Ventilation, A/C (HVAC), and Engine Cooling System Service, Diagnosis, and Repair

   A technician wants to store recovered R-134a in an empty 30 lb disposable (DOT 39) cylinder that virgin R-134a was sold in. Why is this cylinder not used for recovered refrigerant?

   1. Its inner lining reacts with oil in recovered refrigerant.
   2. Its valve draws air in each time it is opened.
   3. It is built and marked as a cylinder that is never refilled.
   4. Its pressure rating is too low for R-134a at shop temperature.
   Show the answer

   C. Correct. A DOT 39 cylinder is a non-refillable cylinder, and federal law forbids transporting one that has been refilled. Recovered or recycled refrigerant goes into a refillable storage tank approved for it and labeled with the refrigerant it holds.

   Why not the others

   A. The trace oil in recovered refrigerant does not attack the cylinder. The cylinder is ruled out because it is a non-refillable type; recovered refrigerant goes into an approved refillable tank.

   B. A cylinder holding refrigerant is above atmospheric pressure, so opening its valve lets refrigerant out rather than drawing air in. The real problem is that a DOT 39 cylinder is designed to be filled only once.

   D. The same cylinder held virgin R-134a at the same temperatures, so its rating is not the issue. It is ruled out because it is built to be filled once and never refilled.

3. Recall · Refrigeration System Component Diagnosis and Repair

   On an expansion-valve A/C system, a receiver/drier is mounted in the liquid line between the condenser and the expansion valve. Which of these is one of its jobs?

   1. Keeping liquid refrigerant out of the compressor
   2. Holding a reserve of liquid for the valve
   3. Metering refrigerant into the evaporator
   4. Turning high-pressure vapor into liquid
   Show the answer

   B. Correct. The receiver/drier stores liquid refrigerant on the high side so the expansion valve has a steady supply of liquid as the cooling load changes, and its desiccant absorbs moisture from the refrigerant. Because the desiccant can hold only so much water, the receiver/drier is replaced whenever the manufacturer's procedure calls for it.

   Why not the others

   A. Keeping liquid out of the compressor is the job of an accumulator, which sits on the low side of an orifice-tube system. A receiver/drier is on the high side and stores liquid for the expansion valve.

   C. The expansion valve, downstream of the receiver/drier, meters the refrigerant. The receiver/drier stores liquid so the valve always has liquid to meter.

   D. The condenser turns the high-pressure vapor into liquid before it reaches the receiver/drier, which then stores that liquid for the expansion valve.

4. Recall · Operating Systems and Related Controls Diagnosis and Repair

   With the blower switch off and the ignition on, a new blower circuit fuse blows the moment it is installed. To find the short to ground without blowing more fuses while the harness is moved and sections are unplugged, which of these can be installed in the fuse's place?

   1. A fuse of the next higher rating
   2. A jumper wire across the fuse terminals
   3. A test light across the fuse terminals
   4. A DMM set to ohms across the fuse terminals
   Show the answer

   C. Correct. The test light's bulb limits the current, and it lights brightly while the short is present; when the shorted section is unplugged or the chafed wire is moved off metal, it goes out. That pinpoints the fault without heating the wiring or using up fuses.

   Why not the others

   A. A larger fuse lets more current through wiring sized for the original fuse, so the wire can overheat before the fuse opens, and with a dead short it still blows. A fuse is never replaced with a higher rating; a test light traces the short safely.

   B. A jumper puts no limit on the current, so the short would draw enough to overheat or burn the wiring. A test light in the fuse's place limits the current and shows when the short is gone.

   D. An ohmmeter is never connected to a powered circuit: the voltage makes the reading meaningless and can damage the meter. A test light in the fuse's place carries a limited current and shows when the short is removed.

5. EXCEPT · Operating Systems and Related Controls Diagnosis and Repair

   With the engine at normal operating temperature, a dual-zone climate system set to 85°F in both zones blows cold air from every outlet. Hot coolant reaches its heater core through an electric coolant control valve. Any of these could be the cause EXCEPT:

   1. a coolant control valve stuck closed.
   2. a compressor clutch that will not engage.
   3. an in-car temperature input reading far too high.
   4. air trapped in the heater core.
   Show the answer

   B. Correct. The compressor only cools and dries the air; heat comes from hot coolant in the heater core, so a compressor that never runs cannot turn heated air cold. Each of the other faults either keeps the core from warming the air or tells the module to cool.

   Why not the others

   A. A valve stuck closed stops hot coolant from reaching the heater core, so neither zone can warm its air even with both blend doors at full heat. Both zones share the core, which fits cold air from every outlet.

   C. If the module believes the cabin is far hotter than the 85°F setting, it drives both blend doors toward full cold to cool it, so cold air can come from every outlet. Comparing the scan-tool in-car reading with a thermometer shows the error.

   D. An air pocket keeps coolant from circulating through the heater core, so the core stays cool and both zones blow cold. Bleeding the cooling system as the manufacturer directs restores the flow.

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