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Question 1HVAC System Components, Operation, and Air Distribution

What is the primary job of the compressor in an automotive air conditioning system?

  1. It condenses refrigerant vapor into liquid by removing heat from it
  2. It removes moisture and debris from the refrigerant charge
  3. It raises refrigerant pressure and moves it through the circuit Correct answer.
  4. It meters liquid refrigerant into the evaporator at a controlled rate

Explanation

The compressor is the only pump in the system; it draws low-pressure vapor from the evaporator outlet and compresses it so the condenser can reject heat. Moving the refrigerant also carries lubricating oil throughout the circuit.

Question 2HVAC System Components, Operation, and Air Distribution

What does the condenser do in an A/C system?

  1. It separates refrigerant oil from the refrigerant vapor
  2. It stores liquid refrigerant until the evaporator needs it
  3. It absorbs heat from the air entering the passenger compartment
  4. It releases refrigerant heat to the outside air Correct answer.

Explanation

High-pressure, high-temperature vapor from the compressor enters the condenser, where outside airflow carries heat away and the refrigerant condenses to a liquid. The condenser is mounted ahead of the radiator or on a body panel to receive airflow.

Question 3HVAC System Components, Operation, and Air Distribution

As refrigerant passes through the evaporator, it...

  1. boils and absorbs heat from air moving across the core Correct answer.
  2. is filtered of metal particles and debris by the accumulator
  3. is cooled by the condenser before it returns to the compressor
  4. is compressed to a higher pressure and temperature by the compressor

Explanation

The expansion device has already lowered the refrigerant's pressure so it boils at a low temperature inside the evaporator. The heat of vaporization is drawn from the air stream, which cools and dehumidifies the cabin air.

Question 4HVAC System Components, Operation, and Air Distribution

A clogged cabin air filter most directly affects which of these?

  1. Engine coolant temperature at the radiator outlet
  2. The volume of air delivered through the vents Correct answer.
  3. The refrigerant charge level in the system
  4. The pressure at which the compressor clutch engages

Explanation

The cabin filter sits in the outside-air or recirculation path ahead of the blower, so a restriction there reduces airflow at every blower speed and every mode. It has no effect on refrigerant pressure or engine cooling.

Question 5HVAC System Components, Operation, and Air Distribution

Why do R-134a and R-1234yf service ports use different fitting designs?

  1. To permit faster evacuation of the system
  2. To prevent charging with the wrong refrigerant Correct answer.
  3. To allow either refrigerant to be used in any system
  4. To identify which service port is the high side

Explanation

Each refrigerant has a unique service-port size and shape so only the matching recovery and charging equipment can be connected. This prevents cross-contamination, which can damage the system and create a handling hazard.

Question 6HVAC System Components, Operation, and Air Distribution

In a typical vehicle, where does passenger-compartment heat come from?

  1. Air warmed as it passes over the condenser
  2. An electric element built into the evaporator case
  3. Refrigerant vapor leaving the compressor
  4. Engine coolant circulating through the heater core Correct answer.

Explanation

The heater core is a small radiator inside the HVAC case; hot engine coolant flows through it and the blower pushes cabin air across its fins. The blend door determines how much air passes through the core versus around it.

Question 7HVAC System Components, Operation, and Air Distribution

What is the purpose of the expansion valve or orifice tube?

  1. To remove moisture and debris from the refrigerant
  2. To lower refrigerant pressure and meter flow Correct answer.
  3. To store refrigerant oil for the compressor
  4. To raise refrigerant pressure before it enters the condenser

Explanation

The expansion device is the dividing point between the high and low sides; it throttles liquid refrigerant so pressure and temperature drop before the evaporator. A TXV varies its opening to hold superheat, while a fixed orifice tube provides a calibrated restriction.

Question 8HVAC System Components, Operation, and Air Distribution

Water accumulating on the passenger floor while the A/C is running is most likely caused by...

  1. An overcharged refrigerant system
  2. A leaking heater core
  3. A failed blower motor
  4. A plugged evaporator drain hose Correct answer.

Explanation

Condensate collected on the evaporator case is routed outside through a drain hose. If the hose or case outlet is blocked, water backs up and spills into the cabin.

Question 9HVAC System Components, Operation, and Air Distribution

On a system with a fixed orifice tube, what does the cycling clutch switch do?

  1. It disengages the clutch at low evaporator pressure Correct answer.
  2. It increases blower speed as the cabin cools
  3. It closes the heater control valve whenever the A/C is on
  4. It disengages the clutch when condenser pressure becomes excessive

Explanation

The cycling switch senses low-side pressure at the accumulator; as the evaporator approaches freezing the pressure drops and the switch opens the clutch circuit. When pressure rises again the clutch re-engages, holding evaporator temperature in a safe range.

Question 10HVAC System Components, Operation, and Air Distribution

What does the accumulator do in a CCOT (cycling clutch orifice tube) system?

  1. It varies the size of the orifice with evaporator load
  2. It keeps liquid refrigerant from reaching the compressor Correct answer.
  3. It stores liquid refrigerant at the condenser outlet
  4. It filters the air entering the blower case

Explanation

In a CCOT system the accumulator sits between the evaporator outlet and the compressor, holding any liquid that did not boil off along with desiccant and a screen. Only vapor is released to the compressor, and the low-pressure cycling switch is often mounted on it.

Question 11HVAC System Components, Operation, and Air Distribution

Where is the receiver-drier located in a TXV system?

  1. Between the evaporator outlet and the compressor inlet
  2. Between the condenser outlet and the expansion valve Correct answer.
  3. In the suction line next to the compressor
  4. Inside the evaporator inlet tank

Explanation

The receiver-drier sits on the high side after the condenser and before the TXV; it stores liquid refrigerant for varying loads and its desiccant removes moisture. Its high-side location is what distinguishes it from an accumulator.

Question 12HVAC System Components, Operation, and Air Distribution

A blower motor works on high speed only. Which is the most likely cause?

  1. A blower motor with a seized bearing and worn brushes
  2. A blower motor with shorted windings drawing excess current
  3. An open blower relay coil that prevents high speed
  4. An open blower resistor Correct answer.

Explanation

Lower blower speeds are produced by routing current through resistor steps or by pulse-width modulation, while the high-speed circuit bypasses them. If only the resistor or control module fails, the direct high-speed path still runs the motor.

Question 13HVAC System Components, Operation, and Air Distribution

A vehicle cools well on the highway but poorly when idling in traffic. Which is the most likely cause?

  1. A low refrigerant charge in the system
  2. A heater core that is bypassing hot coolant
  3. A restricted cabin air filter element
  4. Weak condenser airflow at idle Correct answer.

Explanation

At road speed ram air carries heat out of the condenser; at idle the system depends on the electric fan or fan clutch. If that fan is weak or inoperative, high-side pressure climbs and cooling fades at low speed but returns on the highway.

Question 14HVAC System Components, Operation, and Air Distribution

What does a binary (dual-function) pressure switch do?

  1. It opens the clutch circuit at pressure extremes Correct answer.
  2. It regulates coolant flow through the heater core
  3. It varies blower speed in direct proportion to system pressure
  4. It sets the opening point of the expansion valve

Explanation

A binary switch protects the compressor at both ends of the pressure range, opening the clutch circuit when high-side pressure is excessive and when pressure falls low enough to indicate a loss of charge. A trinary switch adds a condenser fan request.

Question 15HVAC System Components, Operation, and Air Distribution

Which lubricant is required in most R-134a automotive A/C systems?

  1. SAE 30 engine oil from the crankcase
  2. Polyalkylene glycol (PAG) oil Correct answer.
  3. DOT 3 brake fluid from the hydraulic system
  4. Mineral oil, which is used with R-12 systems

Explanation

R-134a does not carry mineral oil reliably, so these systems use PAG oil, often in a specific viscosity called out by the manufacturer. The oil circulates with the refrigerant and must stay compatible and moisture-free.

Question 16HVAC System Components, Operation, and Air Distribution

Airflow from all outlets is weak at every blower speed, and the blower motor sounds normal. Which is most likely?

  1. A blower motor that has failed and does not turn
  2. A restricted cabin air filter Correct answer.
  3. An open blower resistor that limits operation to high speed
  4. An A/C system that is significantly undercharged

Explanation

If the motor runs at every speed but delivers little air, the restriction lies in the air path - a loaded cabin filter, debris in the case, or a clogged evaporator face. Electrical faults in the blower circuit change speed rather than airflow at all speeds.

Question 17HVAC System Components, Operation, and Air Distribution

The engine reaches normal temperature, the heater blows cold, and both heater hoses at the firewall are cool. What is the most likely cause?

  1. The A/C compressor clutch is not engaging
  2. No coolant flow through the heater core Correct answer.
  3. The refrigerant system is overcharged
  4. The condenser cooling fan is inoperative

Explanation

Heat comes from hot coolant flowing through the core. Cool hoses at both fittings mean hot coolant never arrives, pointing to a closed coolant control valve, an air lock, a kinked hose, or a plugged core. If the hoses were hot, the fault would instead be in the air-side doors.

Question 18HVAC System Components, Operation, and Air Distribution

On an HVAC case that uses engine vacuum to position the mode doors, what happens when vacuum is lost?

  1. The doors move to the defrost position Correct answer.
  2. The doors move to the panel position
  3. The doors stay wherever they were when vacuum was lost
  4. The doors cycle continuously between positions

Explanation

Mode actuators are spring-loaded so that losing vacuum produces a fail-safe default of defrost, which keeps the windshield clear. That is why a broken or disconnected vacuum line so often shows up as air stuck on defrost.

Question 19HVAC System Components, Operation, and Air Distribution

A thermostatic expansion valve (TXV) regulates refrigerant flow to maintain a constant...

  1. Superheat at the evaporator outlet Correct answer.
  2. Subcooling at the condenser outlet
  3. Compressor discharge pressure
  4. Blower motor current draw

Explanation

The TXV responds to evaporator outlet temperature and pressure through its sensing bulb and internal passages, opening or closing to hold superheat at a set value. That keeps the evaporator fully utilized without allowing liquid to reach the compressor.

Question 20HVAC System Components, Operation, and Air Distribution

The compressor clutch does not engage, the charge is correct, and there is no voltage at the clutch coil connector with A/C requested. What should be checked next?

  1. The compressor internal reed valves
  2. The evaporator case drain hose
  3. The refrigerant charge level in the system
  4. The clutch control circuit Correct answer.

Explanation

No voltage at the coil means the supply circuit must be traced rather than the coil assumed bad. Fuses, the clutch relay, the pressure switch (which opens on low charge or high pressure), and the control module command all sit upstream of that connector.

Question 21HVAC System Components, Operation, and Air Distribution

Both low-side and high-side gauge readings are below normal, cooling is poor, and the compressor cycles frequently. What is the most likely cause?

  1. The condenser is restricted
  2. The blower motor is drawing excessive current
  3. The refrigerant charge is low Correct answer.
  4. The system is overcharged

Explanation

With less refrigerant in circulation the compressor moves less mass, so both pressures fall and the low-pressure switch cycles the clutch to protect the compressor. The correct repair is to locate and fix the leak before recharging.

Question 22HVAC System Components, Operation, and Air Distribution

The low-side gauge pulls down toward vacuum while the high side reads near normal, and frost forms at the expansion device. What does this indicate?

  1. An inoperative condenser cooling fan that raises high-side pressure
  2. A restriction at the expansion device Correct answer.
  3. An overcharged system
  4. A slipping compressor clutch

Explanation

A restriction blocks flow into the evaporator, so the compressor pulls the low side toward vacuum while the high side stays near normal, and the pressure drop across the restriction produces localized frost. Restoring free flow through the expansion device or orifice tube corrects the readings.

Question 23HVAC System Components, Operation, and Air Distribution

On an automatic climate control system, the small aspirator blower that pulls cabin air across the in-car temperature sensor fails. What is the result?

  1. The heater core will be bypassed by the blend door
  2. Cabin temperature control becomes inaccurate Correct answer.
  3. The compressor clutch will not engage at all
  4. The blower motor will run only on high speed

Explanation

The in-car sensor must continuously sample cabin air, and the aspirator provides that sample. Without it the sensor reads stagnant air near the dash, so the control module miscalculates and discharge temperature wanders or overshoots the set point.

Question 24HVAC System Components, Operation, and Air Distribution

On a CCOT system the compressor runs continuously and the evaporator core ices over. Which is the most likely cause?

  1. A cycling switch that stays closed Correct answer.
  2. A low refrigerant charge in the system
  3. An inoperative condenser fan
  4. A restricted orifice tube

Explanation

The cycling switch is what opens the clutch circuit when evaporator pressure drops to the freeze point. If it never opens, the compressor keeps running, the core falls below freezing, and condensate freezes on the fins and blocks airflow.

Question 25HVAC System Components, Operation, and Air Distribution

Technician A says a variable-displacement compressor can change its stroke to control evaporator pressure without cycling the clutch. Technician B says a fixed-displacement compressor controls evaporator temperature by cycling the clutch. Who is correct?

  1. Neither technician
  2. Technician B only
  3. Both technicians Correct answer.
  4. Technician A only

Explanation

Variable-displacement compressors vary piston stroke, usually through a control valve that responds to suction pressure, so the clutch can stay engaged while output matches demand. Fixed-displacement systems such as CCOT instead cycle the clutch to keep the evaporator from freezing, so both statements are true.

Question 26HVAC System Components, Operation, and Air Distribution

Which statement best describes the job of the condenser in an automotive A/C system?

  1. It stores liquid refrigerant and removes moisture from the system.
  2. It drops refrigerant pressure before the refrigerant reaches the evaporator.
  3. It releases refrigerant heat to the outside air so vapor condenses. Correct answer.
  4. It absorbs heat from the passenger compartment and boils the refrigerant.

Explanation

The condenser is the heat-rejection coil of the system. High-pressure vapor discharged by the compressor gives up heat to the air flowing through the fins and condenses into a liquid, so it leaves the condenser as a high-pressure liquid. Pressure reduction and moisture removal take place at other components.

Question 27HVAC System Components, Operation, and Air Distribution

In a typical HVAC case, what determines how much air passes through the heater core and how much bypasses it?

  1. The mode door position
  2. The refrigerant charge level
  3. The blend door position Correct answer.
  4. The blower motor speed

Explanation

The blend (air-mix) door varies the ratio of air routed through the heater core to air routed around it, so outlet temperature is set by mixing heated and cooled air. The mode door only chooses which outlets receive the air, and blower speed changes volume rather than temperature.

Question 28HVAC System Components, Operation, and Air Distribution

What is the compressor's role in the refrigeration cycle?

  1. It lowers refrigerant pressure so the evaporator can absorb heat.
  2. It removes moisture from the refrigerant before it reaches the expansion device.
  3. It cools the high-pressure refrigerant by passing it through fins at the front of the vehicle.
  4. It raises refrigerant pressure and temperature and circulates the refrigerant. Correct answer.

Explanation

The compressor draws low-pressure vapor from the evaporator and pumps it to a higher pressure, which also raises its saturation temperature so the condenser can reject heat to outside air. In doing so it circulates both refrigerant and lubricating oil through the system.

Question 29HVAC System Components, Operation, and Air Distribution

A system was just serviced. High-side pressure is above normal for the ambient temperature, low-side pressure is slightly above normal, and cooling is poor. The condenser is clean and both cooling fans operate. What is the most likely cause?

  1. The system is low on refrigerant
  2. The system is overcharged with refrigerant Correct answer.
  3. The compressor is worn and not pumping
  4. The condenser has restricted airflow

Explanation

Extra refrigerant backs liquid up in the condenser, reducing the area available for condensing, so high-side pressure climbs above normal and cooling drops off. Because condenser airflow has already been verified as good, an excessive charge is the remaining explanation for the high side being high.

Question 30HVAC System Components, Operation, and Air Distribution

Why does the A/C compressor usually run when the mode selector is set to defrost?

  1. It raises the temperature of the air entering the heater core.
  2. It prevents the evaporator from freezing at low ambient temperatures.
  3. Dehumidified air clears the windshield faster. Correct answer.
  4. It keeps the compressor shaft seal lubricated in cold weather.

Explanation

When the compressor runs, the evaporator removes moisture from the air before that air is reheated and sent to the windshield. Dry air does not re-fog the glass as readily, so the windshield clears faster and stays clear.

Question 31HVAC System Components, Operation, and Air Distribution

On a system equipped with a refrigerant pressure transducer, what does the PCM use that signal for?

  1. To report refrigerant charge weight to the scan tool
  2. To open the heater control valve as pressure rises
  3. To control the compressor clutch and cooling fans Correct answer.
  4. To vary alternator output according to A/C load

Explanation

The transducer produces a voltage that varies proportionally with refrigerant pressure. The PCM uses that input to engage or disengage the compressor clutch for low- and high-pressure protection and to command the cooling fan(s) as pressure rises. Unlike a simple switch, it reports the actual pressure value.

Question 32HVAC System Components, Operation, and Air Distribution

The blower fuse blows as soon as the blower is switched on. The blower wheel turns freely by hand and the wiring harness shows no damage. What is the most likely cause?

  1. A blower motor with an internal short Correct answer.
  2. A blower motor resistor with an open circuit
  3. A blower relay with burned contacts
  4. High resistance in the blower ground circuit

Explanation

A fuse that fails instantly points to excessive current from a short to ground rather than from added resistance. Since the motor turns freely and the harness is intact, the short is most likely inside the motor itself, in the windings or brush area.

Question 33HVAC System Components, Operation, and Air Distribution

The compressor clutch engages, the belt and pulley turn normally, and the charge is correct, but cooling is poor. High-side and low-side readings stay nearly equal to each other and both track ambient temperature. What is the most likely cause?

  1. A restriction in the liquid line
  2. A condenser fan that is not operating
  3. A compressor that is not pumping Correct answer.
  4. A thermostatic expansion valve that has lost its bulb charge

Explanation

When a compressor stops pumping, the high and low sides equalize and both simply follow ambient temperature because no pressure differential is being produced. Because the clutch is engaged and the belt is turning, the fault is inside the compressor, such as failed reed valves, a broken shaft, or worn pistons.

Question 34HVAC System Components, Operation, and Air Distribution

The thermostatic expansion valve on a system sticks in the open position. Which condition is most likely to result?

  1. The high-side pressure falls below the low-side pressure.
  2. Refrigerant oil is trapped in the condenser and the compressor seizes from lack of oil.
  3. The evaporator starves for refrigerant and cools poorly.
  4. Liquid refrigerant reaches the compressor and can damage it. Correct answer.

Explanation

A valve stuck open overfeeds the evaporator, so not all the refrigerant boils before it leaves the coil. Liquid carryover reaches the accumulator or suction line and then the compressor, which cannot compress liquid; the result is slugging, high low-side pressure, and possible internal damage.

Question 35Refrigeration System Components and Operation

What is the primary job of the compressor in an automotive A/C system?

  1. Removes moisture and solid debris from the refrigerant charge
  2. Meters liquid refrigerant flow into the evaporator coil
  3. Circulates engine coolant through the heater core and back to the engine
  4. Raises refrigerant pressure and temperature so heat can be rejected Correct answer.

Explanation

The compressor takes low-pressure vapor from the evaporator and raises its pressure and temperature so the condenser can reject heat to the outside air. It is the only pumping device in the refrigerant circuit and does no drying or metering.

Question 36Refrigeration System Components and Operation

In which component does refrigerant change from a high-pressure vapor to a high-pressure liquid?

  1. The receiver-drier, where the desiccant releases stored heat
  2. The compressor, which cools the gas as it raises its pressure
  3. The evaporator, where the low-pressure liquid absorbs heat
  4. The condenser, where heat is released to the outside air Correct answer.

Explanation

The condenser receives hot high-pressure vapor from the compressor and rejects heat to the air moving across its fins, so the refrigerant condenses into a high-pressure liquid. Condensation is what changes the state; storage, drying, and compression do not.

Question 37Refrigeration System Components and Operation

What happens to the refrigerant as it passes through the evaporator?

  1. It condenses while rejecting heat to the air passing over the fins
  2. It is compressed to a higher pressure before it leaves the coil
  3. It loses pressure as it passes through the desiccant bed
  4. It boils at low pressure while absorbing heat from the air Correct answer.

Explanation

Low-pressure liquid enters the evaporator and boils into vapor, absorbing heat from the air the blower moves across the coil. That heat removal cools and dehumidifies the passenger compartment.

Question 38Refrigeration System Components and Operation

Which statement correctly matches a refrigerant component with the system design that uses it?

  1. A receiver-drier prevents liquid floodback on orifice-tube systems
  2. An accumulator stores liquid refrigerant on expansion-valve systems only
  3. A receiver-drier stores liquid and dries the charge on TXV systems Correct answer.
  4. An accumulator meters the refrigerant flow on expansion-valve systems

Explanation

Expansion-valve systems use a receiver-drier in the high-pressure liquid line to store liquid refrigerant and hold the desiccant. Orifice-tube systems use a low-side accumulator to keep liquid refrigerant from reaching the compressor.

Question 39Refrigeration System Components and Operation

Which statement describes the orifice tube used in a CCOT system?

  1. A small pump that circulates refrigerant through the evaporator coil
  2. A fixed restriction that meters refrigerant into the evaporator Correct answer.
  3. A valve that varies flow continuously in response to evaporator superheat
  4. A bypass that dumps liquid back to the accumulator when the clutch cycles

Explanation

An orifice tube is a calibrated, fixed restriction, usually located in the liquid line at the evaporator inlet on CCOT systems. Because it cannot change size, cooling output is regulated by cycling the compressor clutch rather than by varying the restriction.

Question 40Refrigeration System Components and Operation

The sensing bulb of a thermostatic expansion valve is clamped to the evaporator outlet. What is its function?

  1. It senses evaporator outlet temperature to control superheat Correct answer.
  2. It opens the valve as evaporator pressure rises to prevent freezing
  3. It senses condenser pressure to limit maximum discharge pressure
  4. It measures liquid line temperature so the valve can control subcooling

Explanation

The bulb is charged with refrigerant and responds to the temperature of the line it is clamped to. As outlet temperature changes, bulb pressure changes and repositions the valve, holding a small amount of superheat so liquid does not reach the compressor.

Question 41Refrigeration System Components and Operation

What is the purpose of the high-pressure cutout switch in an A/C system?

  1. It cycles the condenser fan to hold a constant low-side pressure
  2. It opens the liquid line when evaporator pressure drops below freezing
  3. It disengages the compressor clutch when discharge pressure gets too high Correct answer.
  4. It limits blower motor current when duct pressure is high

Explanation

The high-pressure switch interrupts clutch power when discharge pressure exceeds a set limit, protecting hoses, seals, and the compressor from overpressure damage. It normally resets on its own once pressure returns to a safe range.

Question 42Refrigeration System Components and Operation

On a cycling-clutch orifice-tube system, what does the low-pressure switch do?

  1. Controls blower speed as evaporator temperature changes
  2. Opens the system when high-side pressure exceeds the relief setting
  3. Senses discharge pressure and turns on the condenser fan
  4. Disengages the clutch as suction pressure falls near freezing Correct answer.

Explanation

The low-pressure switch opens and closes the clutch circuit in response to suction pressure. As the evaporator approaches freezing, pressure drops and the switch opens the circuit; when pressure rises again, the clutch re-engages.

Question 43Refrigeration System Components and Operation

On a CCOT system, what are the main jobs of the accumulator?

  1. Separate liquid from vapor and hold the desiccant and oil Correct answer.
  2. Meter refrigerant into the evaporator and hold the total charge
  3. Raise suction pressure before the compressor to prevent slugging
  4. Store liquid refrigerant and provide subcooling before the orifice tube

Explanation

The accumulator sits between the evaporator outlet and the compressor. It lets any liquid carried out of the evaporator boil off, returns oil to the compressor, and holds a desiccant bag that absorbs moisture.

Question 44Refrigeration System Components and Operation

Which of these components operates on the low-pressure side of the system?

  1. The accumulator Correct answer.
  2. The receiver-drier
  3. The discharge muffler
  4. The condenser

Explanation

Everything between the expansion device and the compressor inlet is the low side, and the accumulator is located there on CCOT systems. The condenser, receiver-drier, and discharge-line components all see high-side pressure.

Question 45Refrigeration System Components and Operation

Which lubricant is normally specified for an R-134a automotive A/C system?

  1. PAG oil, because it circulates with R-134a and lubricates the compressor Correct answer.
  2. Silicone oil, because R-134a does not attack it
  3. Ester oil, because it is the only lubricant approved for HFC refrigerants
  4. Mineral oil, because it mixes readily with R-134a at low temperature

Explanation

R-134a does not carry mineral oil, so polyalkylene glycol (PAG) oil is used in most R-134a automotive systems; it circulates with the refrigerant and lubricates the compressor. Ester oil appears in some retrofit applications but is not the only approved lubricant.

Question 46Refrigeration System Components and Operation

The electromagnetic clutch on an A/C compressor is energized by:

  1. Battery voltage through the clutch relay and control circuit Correct answer.
  2. The high-side pressure transducer signal only, with no relay in the circuit
  3. The blower motor resistor pack
  4. The evaporator thermistor alone, with no switch

Explanation

The clutch coil is an electromagnet that pulls the drive plate in when the control circuit completes its path through the pressure switches, temperature control, and relay. Current comes from the battery through the relay contacts, not from a sensor signal alone.

Question 47Refrigeration System Components and Operation

What is the function of the pressure relief valve on a compressor or discharge line?

  1. Vent refrigerant if pressure rises above a safe limit Correct answer.
  2. Release oil back to the crankcase during low load
  3. Open the suction line when the evaporator freezes
  4. Bleed air out of the system after a recharge

Explanation

The relief valve is a safety device that opens at a preset high pressure and discharges refrigerant, protecting hoses, seals, and the compressor from rupture. It is not a service or maintenance valve and plays no role in routine charging.

Question 48Refrigeration System Components and Operation

A system has near-normal high-side pressure, low suction pressure, and the liquid line is frosted just downstream of the orifice tube. What is the most likely cause?

  1. A blower motor resistor that is open, stopping the blower
  2. A restriction at the orifice tube or liquid line Correct answer.
  3. A slipping compressor clutch
  4. An overcharge of refrigerant

Explanation

A restriction creates a large pressure drop at that point, so the evaporator is starved and suction pressure falls while the high side stays roughly normal. Refrigerant flashing as it passes the restriction chills that spot, producing frost or heavy sweating on the line.

Question 49Refrigeration System Components and Operation

How does a variable-displacement automotive compressor control its capacity?

  1. It uses a fixed swash plate and cycles the clutch rapidly to change output
  2. It is driven by an electric motor instead of an engine belt
  3. It changes piston stroke to match demand while remaining engaged Correct answer.
  4. It has no clutch and is controlled only by blower speed

Explanation

A variable-displacement compressor changes the angle of its swash plate or wobble plate, which changes piston stroke and therefore how much refrigerant it pumps. That lets it hold steady cooling without constant clutch cycling.

Question 50Refrigeration System Components and Operation

On a system with a sight glass in the receiver, continuous bubbles during steady operation usually indicate:

  1. Normal operation of the expansion valve
  2. An overcharge of refrigerant
  3. Excess oil in the system
  4. A low refrigerant charge Correct answer.

Explanation

Bubbles mean vapor is passing through the liquid line, which normally happens when the charge is low and the line cannot stay full of liquid. With the correct charge the glass remains clear under steady conditions.