A7 Heating &
Air Conditioning
An R-134a system is tested at 85°F ambient. The condenser fins are clean and the cooling fan runs at full speed. Which of these could be the cause of these readings?
| Measurement | Specification | Actual |
|---|---|---|
| Low-side pressure | 25–35 psi | 55 psi |
| High-side pressure | 200–250 psi | 320 psi |
| Center vent temperature | 40–50°F | 62°F |
Technician A says organic acid technology coolant may be topped off with green conventional coolant in an emergency. Technician B says mixing coolant chemistries shortens the additive package service life. Who is right?
Air comes only from the defrost outlets on an electronically controlled HVAC system. Any of these could be the cause EXCEPT:
With the engine at operating temperature, an infrared thermometer shows cold areas across the lower third of the radiator core. Coolant level and cap are correct. Which of these could be the cause?
The high-pressure relief valve mounted on an A/C compressor is designed to:
Technician A says a cooling fan relay may be tested by substituting an identical relay from the same fuse box. Technician B says an inoperative fan can also result from an open module driver circuit. Who is right?
The low-side gauge drops into a vacuum while high-side pressure stays near normal. Frost forms on the liquid line just past the orifice tube. What is the MOST likely cause?
When leak testing with an electronic detector, the probe should be moved:
Which of these is the LEAST likely cause of an exhaust odor entering the cabin with the HVAC set to fresh air?
Cooling is weak, low-side pressure reads high, and high-side pressure reads low. Pressures equalize immediately when the engine is shut off. Which of these could be the cause?
With the A/C requested, the compressor clutch coil draws 0.8 amps at 13.9 volts. Specification is 3.0 to 4.5 amps. This indicates:
Technician A says a mode door actuator with stripped gears will set a bus communication code. Technician B says stripped gears typically set a door position performance code. Who is right?
A pulse-width modulated cooling fan control module allows the fan to:
A serpentine belt squeals on cold start-up and the tensioner arm oscillates heavily at idle. Belt condition and routing are correct. What is the MOST likely cause?
Before removing a Schrader-type service valve core from an A/C line, the technician must:
Cabin air stays warm with the control set to full cold and the A/C on. The blend door actuator sweeps through full travel on command. Which of these could be the cause?
Technician A says an HVAC vacuum reservoir stores vacuum for use during deceleration. Technician B says a vacuum check valve should pass air freely in both directions. Who is right?
Which is the LEAST likely cause of high-side pressure that climbs steadily at idle on a hot day?
A refractometer shows the coolant protects to 0°F. The manufacturer specifies protection to −34°F. The technician should:
The aspirator tube used with an in-car temperature sensor is designed to:
Technician A says a stored P0128 means coolant temperature did not reach the thermostat regulating value in the expected time. Technician B says clearing the code confirms the repair without a drive cycle. Who is right?
The blower operates on all speeds except high, and all other HVAC functions work normally. What is the MOST likely cause?
Only the specified POE refrigerant oil may be used in a hybrid vehicle electric A/C compressor because PAG oil:
Which is the LEAST likely cause of the passenger side blowing hot air while the driver side blows cold?
The compressor clutch will not engage. Static pressure reads 80 psi at 75°F ambient, and the scan tool shows the module commanding the clutch on. Which of these could be the cause?
Reading Your Results: A7 Heating and Air Conditioning, Test 2
This test comes at the same content areas from the gauge set and the service procedure rather than the vents. More of these questions turn on reading two pressures together, on knowing what a refrigerant or coolant service step is protecting against, and on the safety rules that come with the newer systems.
If you missed the questions where two pressures tell the story
A gauge set gives you two numbers, and the relationship between them names the fault far more reliably than either one alone. A low side pulling into a vacuum while the high side stays near normal, with frost at one point in the liquid line, is refrigerant being held back at a restriction, and the frost marks where. A high low-side and a low high-side that equalize the moment the engine is shut off is a compressor that is no longer building a difference between them. High-side pressure climbing steadily at idle on a hot day is heat that is not being rejected, which points at condenser airflow, an overcharge, or air in the system. Read the pair before you read the options.
If you missed the service procedure questions
Several questions here are about doing the job in a way that protects the technician, the equipment, or the system. Certified R-1234yf equipment identifies the refrigerant before it will begin recovery, because a contaminated or mixed charge will ruin the machine and everything it touches afterward. A Schrader core is never removed until the system has been recovered, since the line is under pressure and the core is the only thing holding it. An electronic leak detector probe is moved slowly and low around fittings and seams, because refrigerant is heavier than air and a fast pass will walk right past a small leak. Coolant that tests well short of its specified protection is corrected by adjusting the mix rather than by topping off, and different coolant chemistries are not mixed in an emergency or otherwise.
If you missed the questions built on a measurement
Three questions here give you readings, and each one is asking whether you know what the number is describing.
If you missed the EXCEPT and LEAST likely questions
Four appear on this test, and the method is the same one that works on the real exam. Identify what the three real causes share before hunting for the odd one out. On the defrost-only question, three answers all leave the mode doors unable to move to any other position, and one affects temperature rather than mode. On the dual-zone question, three answers all break the passenger side's ability to control its own blend, and one would affect both sides equally. Naming the shared trait first is faster and far more reliable than working through four options one at a time.