ASE Automobile (A1–A8) — All Questions

In an automotive A/C system, the compressor's job is to:

• a.Store refrigerant
• b.Absorb moisture from the refrigerant
• c.Raise refrigerant pressure and circulate it through the system✓
• d.Condense refrigerant into a liquid

The compressor pressurizes low-pressure refrigerant vapor and pumps it through the system, raising its temperature and pressure before the condenser. It is the pump that drives the refrigeration cycle. A failed compressor clutch or internal damage stops cooling.

The component that changes high-pressure refrigerant vapor into a liquid by removing heat is the:

• a.Expansion valve
• b.Accumulator
• c.Condenser✓
• d.Evaporator

The condenser, mounted in front of the radiator, rejects heat so the high-pressure vapor condenses into a liquid. Airflow across it is essential; a blocked or dirty condenser causes high pressures and poor cooling. The evaporator, by contrast, absorbs heat inside the vehicle.

The evaporator in the passenger compartment:

• a.Rejects heat to the outside air
• b.Stores excess refrigerant
• c.Absorbs heat from cabin air, cooling it✓
• d.Compresses the refrigerant

As low-pressure liquid refrigerant boils in the evaporator, it absorbs heat from the cabin air blown across it, cooling and dehumidifying the air. A restricted or iced evaporator reduces airflow and cooling. Proper refrigerant charge and airflow keep it working correctly.

Technician A says overcharging an A/C system improves cooling. Technician B says overcharging raises system pressures and can reduce cooling and damage the compressor. Who is correct?

• a.Technician B only✓
• b.Both A and B
• c.Technician A only
• d.Neither A nor B

Overcharging raises high-side pressure, reduces cooling efficiency, and can damage the compressor with liquid slugging. The correct charge, measured by weight, is critical. Technician A is wrong; more refrigerant is not better.

The expansion valve or orifice tube controls:

• a.The flow of refrigerant into the evaporator, causing a pressure drop✓
• b.Compressor speed
• c.Blower motor voltage
• d.Cabin air recirculation

The metering device drops the refrigerant pressure and controls flow into the evaporator, allowing it to boil and absorb heat. A restricted orifice or stuck valve causes poor cooling and abnormal pressures. It separates the high side from the low side of the system.

The desiccant in a receiver-drier or accumulator is used to:

• a.Add oil to the system
• b.Absorb moisture from the refrigerant✓
• c.Increase refrigerant pressure
• d.Cool the condenser

The desiccant removes moisture that would otherwise form acids and ice, protecting the system. It should be replaced whenever the system is opened for major service. Saturated desiccant can break down and contaminate the system.

Technician A says a low refrigerant charge typically shows low readings on both gauges with poor cooling. Technician B says the leak should be repaired before recharging to the correct weight. Who is correct?

• a.Neither A nor B
• b.Technician B only
• c.Both A and B✓
• d.Technician A only

An undercharge shows low readings on both gauges with weak cooling and rapid cycling, and any leak must be repaired before recharging by weight. Both technicians are correct. Dye or an electronic detector locates the leak source.

Technician A says cabin heat comes from engine coolant flowing through the heater core. Technician B says a leaking heater core can fog the windshield and leave a sweet smell. Who is correct?

• a.Neither A nor B
• b.Technician B only
• c.Technician A only
• d.Both A and B✓

The heater core transfers heat from hot engine coolant to cabin air, and a leaking core lets coolant fog the glass and produce a sweet odor. Both technicians are correct. A clogged core or low coolant reduces heat output.

Technician A says a stuck-closed blend-air door can cause no heat even with a good heater core. Technician B says a failed blower motor can cause no airflow from the vents. Who is correct?

• a.Technician B only
• b.Technician A only
• c.Both A and B✓
• d.Neither A nor B

A blend door controls how much air passes over the heater core, so a stuck door can cause no heat, and a failed blower stops airflow entirely. Both technicians are correct. Actuator and door faults are common causes of temperature-control complaints.

Before servicing an A/C system, refrigerant must be:

• a.Mixed with fresh oil
• b.Vented outdoors quickly
• c.Recovered with approved equipment, not vented to the atmosphere✓
• d.Frozen in the condenser

Regulations require recovering refrigerant with certified equipment rather than releasing it, because it is a controlled substance. Recovery, recycling, and recharging equipment protects the environment and allows accurate recharging. Technicians handling refrigerant must be certified.

An A/C compressor clutch that will not engage could be caused by all of the following EXCEPT:

• a.A low-refrigerant lockout from the pressure switch
• b.A clogged cabin air filter✓
• c.A blown clutch fuse or relay
• d.An open clutch coil

The clutch may fail to engage due to a low-charge lockout, electrical faults, or an open coil, but a dirty cabin filter only reduces airflow, not clutch engagement. Diagnosis checks power, ground, and the pressure switches. A cabin filter affects volume, not the refrigerant cycle.

Higher-than-normal readings on both the high and low sides of an A/C system, with poor cooling, could indicate:

• a.A stuck-open thermostat
• b.An overcharge or a condenser airflow/cooling problem✓
• c.An open blower resistor
• d.A low refrigerant charge

High readings on both gauges often point to an overcharge or inadequate condenser cooling from a blocked condenser or inoperative cooling fan. Verifying charge weight and fan operation is the next step. Correcting airflow and charge restores normal pressures.

R-1234yf, used in newer vehicles instead of R-134a, is notable because it:

• a.Is chemically identical to the older R-12 refrigerant it replaced
• b.Can be freely mixed with R-134a in any proportion without a problem
• c.Requires no special handling, fittings, or recovery equipment at all
• d.Has a much lower global-warming impact and is mildly flammable✓

R-1234yf was adopted for its low global-warming potential, but it is mildly flammable and must not be mixed with other refrigerants. It uses unique fittings and equipment to prevent cross-contamination. Correct identification and handling are required.

The high-side and low-side service ports on a modern A/C system use different fitting sizes so that:

• a.Refrigerant is able to flow through the system at a much faster rate
• b.Equipment cannot be connected to the wrong side✓
• c.The compressor runs at a cooler temperature during heavy cooling loads
• d.Compressor oil is automatically added to the system during operation

Different quick-couple sizes on the high and low sides prevent connecting the manifold set or charging equipment backward. This protects the technician and the system. The ports are also marked H and L.

A manifold gauge set connected to an A/C system is used to:

• a.Check the remaining tread depth on each of the vehicle's tires
• b.Test the vehicle battery's voltage and cold-cranking performance
• c.Read high- and low-side pressures for diagnosis✓
• d.Measure the engine's oil pressure at idle and at operating speed

The manifold gauges show both system pressures, which the technician interprets to judge charge level, restrictions, and component operation. It also controls evacuation and charging. Pressure readings are compared with ambient temperature.

Before recharging an A/C system that has been opened, the system should be:

• a.Pressurized with ordinary compressed shop air to check for leaks
• b.Evacuated with a vacuum pump to remove air and moisture✓
• c.Placed in a freezer overnight to condense the remaining moisture
• d.Filled quickly with refrigerant without pulling any vacuum first

Pulling a deep vacuum removes non-condensable air and lowers the boiling point of any moisture so it evaporates and is drawn out. Moisture left inside forms acids and ice. A proper evacuation precedes charging by weight.

Using the wrong or incompatible compressor oil in an A/C system can cause:

• a.Poor lubrication and compressor damage✓
• b.A stronger and hotter output from the vehicle's cabin heater core
• c.A faster windshield defrost with no effect on the compressor at all
• d.A noticeable increase in the vehicle's overall highway fuel economy

A/C compressors require the specific oil type for their refrigerant; the wrong or contaminated oil breaks down lubrication and can destroy the compressor. PAG and POE oils are matched to system requirements. The correct oil and amount are specified by the manufacturer.

The air gap on a magnetic A/C compressor clutch is important because:

• a.It controls the blower motor speed selected on the HVAC control head
• b.Too large a gap can keep the clutch from engaging✓
• c.It cools the condenser by directing extra airflow across its fins
• d.It sets the exact refrigerant charge weight for the whole system

The clutch engages when the coil pulls the plate across the air gap; if the gap grows too wide, the clutch slips or will not engage. The gap is measured and shimmed to spec. A worn or improperly gapped clutch causes intermittent cooling.

A low-pressure cutout switch in an A/C system protects the compressor by:

• a.Adding more refrigerant into the system automatically when it runs low
• b.Opening the blend-air door to direct additional air over the core
• c.Disengaging the clutch when pressure or charge is too low✓
• d.Increasing the blower motor speed to move more air across the coils

If the charge drops too low, the low-pressure switch cuts the clutch so the compressor is not run without adequate refrigerant and oil circulation. This prevents damage from lack of lubrication. It is a common reason a clutch will not engage.

A high-pressure cutout switch is used to:

• a.Charge the vehicle's battery through the air conditioning system
• b.Shut off the compressor if pressure rises dangerously high✓
• c.Boost the output of the cabin heater when the engine is fully warm
• d.Regulate the flow of engine coolant through the heater core

The high-pressure switch or transducer disengages the clutch or signals the module when pressures climb too high, protecting components from a blocked condenser or overcharge. It works with the fan controls to manage pressure. Excess pressure can rupture parts if unchecked.

In an orifice tube (CCOT) A/C system, the accumulator is located:

• a.On the high-pressure liquid line, before the condenser inlet fitting
• b.Inside the compressor housing between the pistons and the reed valves
• c.Within the heater core assembly on the passenger cabin side of the case
• d.On the low-pressure suction side, after the evaporator✓

The accumulator sits on the suction line in orifice-tube systems to store excess refrigerant and protect the compressor from liquid slugging, and it holds desiccant. A receiver-drier, by contrast, is used on the liquid line of expansion-valve systems. Its location matches the metering device type.

The receiver-drier in a thermostatic expansion valve (TXV) system is located:

• a.Inside the blower motor housing on the passenger side of the case
• b.On the low-pressure suction line just after the evaporator outlet
• c.On the high-pressure liquid line, before the expansion valve✓
• d.Within the radiator core alongside the engine coolant passages

The receiver-drier stores liquid refrigerant and removes moisture on the high side ahead of the TXV, ensuring only liquid reaches the valve. Orifice-tube systems instead use a suction-side accumulator. Matching the component to the system type is important during service.

An evaporator that repeatedly freezes over, cutting off airflow, is often caused by:

• a.A control that fails to cycle the compressor off in time✓
• b.A leaking axle seal letting gear oil reach the brake linings
• c.A worn front wheel bearing that drones and roughens with speed
• d.A cracked engine exhaust manifold ticking loudly on a cold start

If the compressor does not cycle off as the evaporator nears freezing, condensation freezes on the fins and blocks airflow. A thermostat, temperature sensor, or pressure switch normally prevents this. Restoring proper cycling stops the icing.

A blower motor that works only on the highest speed, with lower speeds dead, most likely has:

• a.A stuck blend-air door leaving the vent temperature uncontrollable
• b.A clogged orifice tube restricting refrigerant into the evaporator
• c.A low refrigerant charge that shows low on both service gauges
• d.A failed blower motor resistor or speed control module✓

The resistor pack or solid-state control sets the lower fan speeds, so its failure often leaves only high speed working, which bypasses the resistor. Replacing the resistor or module restores all speeds. A blower that does not run at all points elsewhere.

A stuck blend-air door actuator will most likely cause:

• a.A dead battery that cannot start the vehicle after it sits overnight
• b.A refrigerant leak from the low side that slowly empties the system
• c.A brake pull to one side felt whenever the vehicle is slowed down
• d.Incorrect or uncontrollable vent temperature✓

The blend door meters air across the heater core to set temperature, so a stuck actuator leaves the output stuck hot, cold, or unresponsive to the controls. Actuators can be tested and recalibrated or replaced. Clicking noises often signal a failing actuator.

A dirty or clogged cabin air filter most commonly causes:

• a.Reduced airflow from the dashboard vents✓
• b.A compressor clutch that stays engaged and will not release at all
• c.A sudden high-side pressure spike that trips the cutout switch
• d.A refrigerant overcharge that raises the system's high-side pressure

A restricted cabin filter chokes the air the blower can move, so vent output drops even though the system is otherwise fine. Replacing the filter restores airflow. It also affects both heating and cooling volume.

An A/C performance test is typically evaluated by measuring the:

• a.Engine oil pressure at idle and again at normal operating speed
• b.Battery cold-cranking amps under load with a carbon-pile tester
• c.Vent discharge air temperature plus the system pressures✓
• d.Tire tread depth at several points across each of the four tires

Technicians judge A/C performance by the temperature at the center vent, together with high- and low-side pressures at a known ambient temperature and humidity. These readings reveal charge and component problems. Manufacturer specs give the target vent temperature.

A very low low-side pressure with frost forming at the metering device inlet usually indicates:

• a.A restriction at the orifice tube or expansion valve✓
• b.A worn front wheel bearing that drones and roughens with speed
• c.An overcharge of refrigerant that raises pressure on both service sides
• d.A slipping serpentine belt that cannot fully drive the compressor

A blockage at the orifice or a stuck-closed expansion valve starves the evaporator, dropping low-side pressure and causing localized frost from the pressure drop at the restriction. Cooling suffers because little refrigerant flows. Replacing the metering device or clearing the restriction restores flow.

In a system with a heater control valve, no cabin heat could be caused by the valve being:

• a.Frozen solid by the cold evaporator core mounted next to it
• b.Stuck wide open and sending too much refrigerant into the evaporator
• c.Electrically bypassed by the blower motor speed control resistor
• d.Stuck closed and blocking coolant to the heater core✓

A heater control valve regulates hot coolant to the core; if it sticks closed, no hot coolant reaches the core and there is no heat. A stuck-open valve can make heat hard to shut off. Not all vehicles use such a valve, relying on the blend door instead.

No cabin heat with the engine at normal temperature and a full cooling system is often caused by a:

• a.Low refrigerant charge reading low on both of the service gauges
• b.Clogged heater core or a stuck blend-air door✓
• c.Worn compressor clutch that slips and cannot drive the compressor
• d.Faulty high-pressure cutout switch on the refrigerant high side

With the engine warm and coolant full, a lack of heat points to restricted coolant flow through the core or a blend door not directing air over it. Flushing the core or repairing the actuator restores heat. Refrigerant components affect cooling, not heating.

In an automatic climate control system, the in-car temperature sensor is used to:

• a.Measure refrigerant pressure on the high and low sides of the system
• b.Provide feedback so the system holds the set temperature✓
• c.Read the individual wheel speeds for the traction control system
• d.Sense the engine oil level and warn the driver when it drops low

The in-car sensor tells the module the actual cabin temperature so it can adjust blend, blower, and compressor to hold the setpoint. A faulty or blocked sensor causes poor temperature control. A small aspirator fan often draws air across it.

Refrigerant leaks are commonly located using:

• a.An electronic leak detector or UV dye with a UV light✓
• b.A test light probed across the vehicle battery's positive terminal
• c.A compression tester threaded into each of the engine's spark plug holes
• d.A vacuum gauge connected to a port on the engine's intake manifold

An electronic sniffer or fluorescent dye traced with a UV lamp pinpoints where refrigerant is escaping. The leak must be repaired before recharging. Soap solution can help confirm a suspected spot.

Severe internal compressor failure that spreads metal debris through the system requires:

• a.Flushing or replacing contaminated parts and adding a filter✓
• b.Replacing only the cabin air filter and returning the vehicle to service
• c.Only adding a larger amount of fresh refrigerant to flush the debris out
• d.Simply raising the engine idle speed to spin the new compressor faster

When a compressor comes apart, debris and acid contaminate the system, so the affected parts are flushed or replaced and an inline filter is often added to protect the new compressor. Simply installing a compressor invites repeat failure. Proper cleanup and oil balancing are essential.

The condenser cooling fan should run when the A/C is on because it:

• a.Cools the front brake rotors during repeated hard braking on descents
• b.Charges the vehicle's battery whenever the engine is at operating speed
• c.Provides airflow so the condenser can reject heat✓
• d.Increases the fuel pressure delivered to the engine's fuel injectors

The condenser needs airflow to condense the refrigerant; at idle or low speed the electric fan supplies it, so a fan failure raises high-side pressure and hurts cooling. The module commands the fan based on A/C and pressure inputs. Verifying fan operation is part of A/C diagnosis.

High high-side pressure with normal or low low-side pressure and poor cooling often indicates:

• a.A worn tie rod end introducing play into the vehicle's steering
• b.A low refrigerant charge that reads low on both of the service gauges
• c.A condenser airflow problem or a system overcharge✓
• d.Air that has become trapped inside one of the hydraulic brake lines

Restricted condenser airflow, from a blocked condenser or a dead fan, or an overcharge, raises high-side pressure and reduces cooling. Verifying fan operation, condenser cleanliness, and charge weight isolates it. Correcting airflow or charge normalizes pressures.

Before recovering refrigerant from an unknown system, a technician should:

• a.Add fresh compressor oil to the system to protect the recovery machine
• b.Disconnect the vehicle battery to prevent the compressor from cycling
• c.Run the engine at full throttle to warm the refrigerant before recovery
• d.Check it with a refrigerant identifier for contamination✓

A refrigerant identifier verifies the type and purity so contaminated or mixed refrigerant is not pulled into the shop's clean recovery tank. Cross-contamination ruins equipment and refrigerant. This check protects the machine and future jobs.

An A/C compressor clutch that stays engaged and will not disengage could be caused by a:

• a.Low refrigerant charge that reads low on both of the service gauges
• b.Clogged orifice tube starving the evaporator of liquid refrigerant
• c.Stuck (welded) clutch relay or a control-circuit fault✓
• d.Torn cabin air filter that restricts airflow through the HVAC case

A relay with welded contacts or a shorted control circuit can keep power on the clutch coil so it never releases. Checking the relay and control signal isolates it. A clutch that never disengages can overcool or overwork the system.

A musty or moldy smell when the A/C first turns on is most often caused by:

• a.Microbial growth on the damp evaporator, often from a blocked drain✓
• b.A refrigerant overcharge that raises pressure on both service gauges
• c.A cracked condenser leaking refrigerant into the airflow at the front
• d.A worn compressor clutch that slips under load and cannot engage

Moisture condensing on the cold evaporator can grow mold, producing a musty odor, especially if the condensate drain is blocked and water pools. Cleaning or treating the evaporator and clearing the drain helps. Running the fan to dry the core before shutdown reduces it.

Charging an A/C system by weight (the specified amount) is preferred over charging by pressure because it:

• a.Is required only on older systems that still use R-12 refrigerant
• b.Gives the exact correct charge regardless of conditions✓
• c.Lets the technician ignore the system's rated refrigerant capacity
• d.Uses far less service equipment than any other charging method available

The manufacturer specifies an exact refrigerant weight, and charging to that weight avoids the errors of estimating by pressure, which varies with temperature and humidity. Precise charge maximizes cooling and protects the compressor. A recovery/recharge machine measures the charge accurately.

A cracked or leaking heater core will typically produce:

• a.A refrigerant leak from the low side along with unusually warm vents
• b.A sweet smell, foggy windows, and coolant loss✓
• c.A high, hard brake pedal that requires extra effort to fully stop
• d.An overcharged battery from extra load placed on the alternator

Coolant leaking from the heater core inside the dash fogs the glass with a sweet-smelling film and slowly drops the coolant level. The core is pressure-tested and replaced. A greasy film on the windshield is a classic sign.

The mode (air distribution) doors in the HVAC case control:

• a.Whether air comes from the dash, floor, or defrost outlets✓
• b.The temperature of the engine coolant flowing to the heater core
• c.The exact refrigerant charge weight held within the A/C system
• d.The alternator output that charges the battery while driving

Mode doors direct the conditioned air to the panel, floor, defrost, or a blend of outlets as selected. A stuck mode door or actuator leaves airflow at the wrong vents. They are separate from the blend (temperature) door.

Selecting recirculation mode on the HVAC controls causes the system to:

• a.Add more refrigerant into the system to lower the vent temperature
• b.Draw air from inside the cabin rather than from outside✓
• c.Route the incoming air around the evaporator, bypassing the coil
• d.Increase the engine's idle speed to spin the compressor faster

Recirculation closes the fresh-air door and reuses cabin air, which cools faster on hot days and blocks outside odors. A stuck recirculation door can cause weak defrost or stale air. Fresh-air mode brings in outside air for ventilation and defrosting.

A blower motor that does not run at any speed, with a good fuse, most likely has a:

• a.Failed motor, connector, or control switch or module✓
• b.Stuck expansion valve starving the evaporator of liquid refrigerant
• c.Low refrigerant charge that reads low on both of the service gauges
• d.Clogged condenser restricting airflow at the front of the vehicle

No operation at any speed points to the motor itself, its wiring/connector, or the control circuit rather than the resistor, which affects only lower speeds. Power, ground, and control signal are checked at the motor. A common failure is the motor or a burned connector.

A refrigerant identifier is connected before recovery mainly to protect the shop's:

• a.Recovery machine and refrigerant supply from contamination✓
• b.Engine oil supply from being diluted by refrigerant during the process
• c.Battery charger from an electrical overload while the system runs
• d.Brake fluid reservoir from absorbing moisture out of the humid air

Identifying the refrigerant first prevents pulling sealants, air, or mixed refrigerants into the clean recovery tank and machine. Contamination can ruin the equipment and the recovered supply. It is a quick check that safeguards costly gear.

Technician A says an overcharged A/C system can raise high-side pressure and reduce cooling. Technician B says inadequate condenser airflow can do the same. Who is correct?

• a.Technician B only
• b.Technician A only
• c.Both A and B✓
• d.Neither A nor B

Both an overcharge and poor condenser airflow drive up high-side pressure and hurt cooling. Both technicians are correct. Verifying charge weight and fan operation separates the two causes.

Technician A says refrigerant must be recovered rather than vented. Technician B says a technician handling refrigerant must be certified. Who is correct?

• a.Neither A nor B
• b.Both A and B✓
• c.Technician B only
• d.Technician A only

Regulations require recovering refrigerant with approved equipment and having certified personnel handle it. Both technicians are correct. This protects the environment and ensures proper service.

Technician A says a low refrigerant charge shows low readings on both gauges. Technician B says any leak should be repaired before recharging. Who is correct?

• a.Both A and B✓
• b.Technician B only
• c.Technician A only
• d.Neither A nor B

An undercharge reads low on both sides with weak cooling, and the leak must be fixed before recharging by weight. Both technicians are correct. Dye or an electronic detector locates the leak.