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65 terms


Heating, Ventilation, Air Conditioning
Tech A says that evacuating an AC system will remove air and moisture from the system. Tech B says evacuating an AC system removes dirt particles. Who is right?
A. Evacuating the system removes air and moisture. The receiver drier may contain a filter or strainer to catch and trap foreign particles and dirt, but this remains in the drier and is not removed during evacuation.
There is a growling/rumbling noise at the AC compressor when the system is off and the engine is running. The noise stops when the system is turned on.Tech A says that a bad compressor bearing could be the cause. Tech B says that a bad compressor clutch bearing could be the cause. Who's correct?
B. The compressor clutch bearing allows the rotor/pulley assembly to spin independently of the compressor shaft when the AC is off. When the AC is on, the rotor/pulley assembly and the armature are locked together by the magnetic action of the compressor clutch coil.
The readings on a manifold gauge are 5psi low and 80 psi high with the AC system operating at an ambient temp of 85 degrees Farenheit. What do the readings indicate? Normal operation, low refrigerant level, a restriction on the high side, or a damaged compressor?
B. Low pressure on both the high and low side indicates a low refrigerant charge.
Recovery/recycling equipment must have shutoff valves located within 12 in of the hose's service ends so that:
oil can be added to the refrigerant
the unit can be isolated from the refrigerant source
the filter can be changed without disconnecting the hoses
refrigerant discharge can be kept to a minimum
D. According to the Clean Air Act, recovery/recycling equipment must have shutoff valves located within 12 in. of the hoses' service ends so that refrigerant discharge to the atmosphere is kept to a minimum.
When recovering refrigerant from an AC system how long should the tech wait after the recover/recycle unit has been turned off to check residual pressure in the system?
1 minute
5 minutes
10 minutes
15 minutes
B. the tech should wait five minutes and watch the gauges to check for residual pressure. If there is, repeat the process to remove any remaining refrigerant until the AC system holds a stable vacuum for 5 min.
A system with a low pressure on the low side and heavy frost accumulation on the inlet side of a TXV indicates:
TXV stuck open
Clogged condenser
Defective compressor
clogged screen or TXV stuck closed
D. A low pressure reading on the low side and a heavy frost accumulation on the inlet side of the TXV indicates a clogged screen at the expansion valve or a TXV stuck closed.
A blower motor only works on high. Which of the following is most likely?
Defective blower relay
Defective resistor
Defective blower switch
Blown fuse or tripped circuit breaker
B. D is incorrect because if the blower fuse was blown or circuit breaker tripped, the blower would not work at all. Answer A is incorrect because a blower relay is generally only used for the high blower speed and this is working. Answer C, the blower switch is a possible cause but the mostly likely cause for operation on high only is that a portion of the resistor assembly is burnt out.
A customer complains that when accelerating his car with the ac on the cold air flow from the dash outlets shifts to the floor. Tech A says that this is caused by a faulty check valve in the vacuum resevoir. Tech B says this condition is due to a vacuum leak. Who is correct?
C. If, during hard accel, air routing changes by itself, it's probably due to a leak in the system or a faulty check valve in the vacuum resevoir. A complaint that the mode shifts from dash to floor at WOT is evidence that the system is not holding vacuum.
When pressure testing the cooling system on a late model gas engine the pressure on the tester drops but no leaks can be found in the engine compartment. Tech A starts the engine and seeing the pressure on the tester increase says that there is an internal leak, a blown head gasket. Tech B says that there cannot be an internal leak because the engine oil looks normal, not milkly like it would be if coolant were present, and there is no white smoke coming from the exhaust pipe. Who is right?
A. If the engine is started while pressure testing a cooling system and the pressure immediately increases, there could be a head gasket leak but not into the crankcase. The coolant may be going out tailpipe but since this is a late model gas engine equipped with a CAT converter, there is no white smoke from the exhauset because the converter super heats the coolant into such a fine vapor that it is not noticeable.
When IDing an AC system Tech A says that an accumulator located between the evaporator and the compressor is an indication that the system has an orifice tube. Tech B says that when the high side service port fitting is small er than the one on the low side the system uses R134A. Who is right?
A. Systems using an expansion valve have a receiver drier between the valve and condenser, while orifice tube systems have an accumulator between the evaporator and compressor. Tech B is wrong because on R 134A the low side service port is the smaller one.
When troubleshooting an ATC system the system responds when the ambient and in vehicle temp sensors are heated and cooled. However there is no response when the sunload sensor is exposed to a light source. Tech A says that the problem is with the system's programmer. Tech B says it is probably the sunload sensor. Who is correct?
B. If the system reacts with a change to one or two inputs but not to the third, the problem is most likely confined to the single sensor or its circuit. But if no reaction is observed on any of the units, or only a partial reaction is seen, the problem is usually with the programmer.
The following are all methods of orifice tube replacement EXCEPT:
Replace the line that incorporates the orifice tube
Disconnect the liquid line from the evap inlet and pull the tube out with the extracting tool
Disconnect the liquid line from the evap inlet line, using a twisting motion, pull the orifice tube out with the extractor tool
Cut out the section of line that contains the orifice tube and using a kit install a new orifice tube segment.
C. When removing the orifice tube with an extractor tool, do not twit or rotate the orifice tube in the line as it can break. If an orifice tube breaks during removal, special tools are available to extract broken orifice tubes. All of the other answers are methods of orifice tube replacement.
When converting the ac system in an older vehicle to R134a what percentage of the original R12 charge amount should be used?
D. When charging a retrofitted system with R134a refrigerant the system will only require 80-90% of the R12 charge amount.
A vehicle with R134a refrigerant inthe ac system has a refrigerant leak. Tech A says that a propane gas leak detector should be used to find the leak. Tech B says an electronic detector should be used. Who's right?
Tech A is wrong because propane gas leak detectors cannot detect R134a.
Which of the following is a TRUE statement about R134a?
It is harmful to the ozone
It mixes with mineral oil
It requires a different dessicant than R12
it operates at lower pressures than R12
C. Desiccants are not universal and different types must be used with differetn refrigerants and lubricating oils. When a system is retrofitted the replacement drier or accumulator has XH7 or XH9 desiccant.
The compressor in an AC system does not run. When a jumper wire is used to connect the battery positive terminal to the power connector the clutch engages. Tech A says the clutch coil is bad. Tech B says the pressure cycling switch could be defective. Who's right?
B. A is wrong because if the clutch coil was defective the compressor clutch would not engage. B is correct because, since the compressor engages when 12v is directly applied, the problem is in the control circuit which includes the pressure cycling switch.
The floor inside a vehicle is wet and there is a slimy film on the windows. Tech A says the heater core is leaking. Tech B says the evaporator case drain plug is clogged. Who is right?
A. Fogged windows that smear when wiped and moisture on the passenger floor are telltale signs of a leaking heater core. Tech B is incorrect because while a clogged evap case drain could cause the case to fill up with moisture and spill onto the floor, it would not cause a slimy film on the window.
During AC system operation a knocking sound can be heard coming from the compressor. Tech A says there can be internal compressor damage. Tech B says that the compressor mounting brackets and bushings should be checked. Who is right?
C. Knocking noises usually indicate internal damage especially on the piston type compressors. Howerver, always check the mounting and brackets before condemning the compressor for noise. A loose mounting can cause knocking noises from the compressor area that may be mistaken for internal noise.
All of the following could cause poor heating performance EXCEPT:
Defective temperature blend door actuator
Radiator coolant temp below 150 degrees
Heater core return hose much cooler than inlet hose
stuck open heater control valve
D. A stuck open heater control valve woulc cause problems when heat is not wanted, but because coolant flow to the heater core is not interrupted, the heater valve would not cause poor performance.
During a performance test the air temp at the center outlet duct is warm to slightly cool and the low and high side pressures on the manifold gauge set are both low. All of the following could be the cause of these symptoms EXCEPT:
Clogged orifice tube
Expansion valve stuck closed
Restricted reciever drier
Plugged condenser
Although the air temp at the center outlet would be about the same, if the condenser is plugged, the manifold gauge readings would be high.
What is the minumum system pressure necessary to leak test with an electronic leak detector?
100 psi
B. There must be at least 50psi of refrigerant pressure in the system in order for a leak detector to be able to sense a leak. Refrigerant may have to be added to the system to achieve this.
Tech A says that when retrofitting an AC system the new R134a ports are installed on the old fittings. Tech be says that if the old fittings arent converted the should be labeled. Who is right?
A. During a retrofit the new R134a service fittings are usually installed on the existing R12 fittings. Tech B is wrong because, if the R12 fittings are not converted, they must be permenantly capped.
When Diagnosing an ATC system most of the system temp sensors can be tested for:
Resistance and current flow
resistance and voltage drop
voltage drop and current flow
current flow and continuity
B. Most temp sensors can be tested for voltage drop and resistance. In general, the sensor should be replaced if its resistance is not within spec. Since a temp sensor's resistance varies with temp, check the voltage against temp and compare to manufacturer spec.
During an AC system test the high side pressure was found to be excessive and the compressor continued to run. Tech A says the high pressure cut out switch could be defective. Tech B says there can be an air flow obstruction at the condenser. Who is right?
C. Tech A is right because the high pressure cut out switch should break the circuit to the compressor if it detects pressures above the preset level. B is riht because an obstruction to air flow thru the condenser can cause excessive high side pressure.
The compressor cycles quickly and air coming from the vents is only slightly cool. Tech A says the problem could be a low refrigerant charge. Tech B says it could be a defective thermostatic switch. Who is right?
C. During operation the clutch may cycle on and off several times per minute. A defective thermostatic switch may not be engaging the compressor long enough; also, if the refrigerant level is low, it will cause the clutch to cycle quickly.
To properly evacuate an AC system the vac pump should be run for:
5 min
10 min
20 min
30 min
D. To properly evacuate an AC system the vacuum pump should be operated at minimum for 30 minutes.
Tech A says a special tool is needed to disconnect and connect spring lock fittings. Tech B says when assembling spring lock fittings new O rings lubricated with clean refrigerant oil should be used. Who is right?
B. A is wrong because the special tool is only required to DISCONNECT the spring lock fittings.
All of the following are true statements concerning in line filters EXCEPT
They are usually installed in a system that has suffered compressor failure
They are installed to protect the new compressor from metal chips or other debris that could still be in the system
They are installed to collect debris that could clog the orifice tube or expansion valve filters
Filters are only installed in the high side of the system
D. There are filters that fit into the high and low sides of the system. All of the other statements are true concerning in line filters.
2 techs are talking about sight glass observations. Tech A says that if foam is seen, the refrigerant charge is low. Tech B says that if oil streaks are seen in the sight class the refrigerant is low. Who is right?
C. If there is foam the charge is low, but if there are only a few bubbles, it is probably OK. Oil streaks in the sight glass usually indicate a low charge and that the compressor is pumping oil from its sump.
Tech A says that moisture in the system can freeze in the expansion valve and stop the system from cooling. tech B says that moisture in the system will react with R12 to form a corrosive acid. Who is right?
C. Moisture in the system can ice up in the TXV and block refrigerant flow. On systems with R12 moisture can combine with the chlorine in R12 to form hydrochloric acid, which can corrode metals and attack rubber parts.
Low heater output can be caused by all EXCEPT
An engine low on coolant
Stuck open t stat
restricted heater control valve
disengaged clutch radiator fan
D. A disengaged clutch type radiator fan would not cause low heater output.
High side pressure in a system is above spec. All of the following can cause this except:
overcharging the system
restricted air flow across the condenser
slipping fan belt
broken compressor reed valve
D. A broken compressor reed valve could not cause the high side pressure to be above spec.
When filling a container with recycled refrigerant to what % should teh container be filled?
B. To prevent overfilling during refrigerant transfer never fill a container to more than 60% its gross weight rating.
A vac door actuator is being tested. When vac is applied wtih a pump the door does not move and the reading on the gauge is 0. Tech A says it is because the door is binding or obstructed. Tech B says the actuator is defective. Who's right?
B. Regardless of what condition the door is in, the key here is that the gauge is reading zero, meaning there is a vac leak in the actuator.
Customer complains of a foul odor from the dash when the AC and blower are on. Tech A says a clogged evaporator drain is the cause. Tech B says it's caused by bacteria growing on the evaporator. Who is right?
C. If the drain at the bottom of the evap case becomes clogged and water collects and stagnates, or if the surface of the evaporator remains too moist due to high humidity, bacteria can grown in the stagnant water or on the evaporator surface and cause an odor.
When an AC system is operating a clicking or buzzing is heard from the compressor. Tech A says the system is overcharged. Tech B says the noise is due to air in the system. Who is right?
C. A clicking or buzzing noise coming from the compressor is a sign that the system is overcharged and liquid refrigerant is entering the compressor. Unless some refrigerant is removed, severe compressor damage may result. The noise could also result from air in the system.
A customer compalins when parallel parking the car stalls w the AC on. Tech a says the power steering pressure switch is bad. Tech B says the problem is with the pump. Who is right?
A. The power steering pressure switch in installed in the power steering system and reports on high pressure conditions caused by load placed on the engine by the pump. The computer may decide to temporarily shut down the compressor to prevent engine stalling or low idle speed, or it could raise idle speed through control of an idle speed control device. If the increased pressure is not being communicated to the computer by the switch, the AC compressor will continue to run with its load on the engine or the idle speed will not be raised high enough to prevent a stall. B is wrong because if the problem was with the pump it would stall regardless if the AC was on or not.
All of the following are true statements about reciever driers EXCEPT
They may have a sight glass at the top
The store liquid refrigerant
They keep liquid refrigerant from entering the compressor
They contain a dessicant to absorb moisture from the system
C. The drier is located in the high side of the system between the condenser and evaporator, ahead of the expansion valve. It stores liquid refrigerant until needed by the evaporator. The accumulator is the component that keeps liquid refrigerant from entering the compressor, but accumulators are used in systems with orifice tubes, not expansion valves.
Tech A says the pressure cycle switch is located on the accumulator. Tech be says there must be an evac/recharge done before removing this switch. Who is right?
A. The pressure cycling switch senses the low side pressure near the evaporator outlet and is usually found on the evaporator. Tech B is wrong because the switch is often mounted in a Shrader valve so it can be replaced without refrigerant loss.
Tech A says that the AC system can be charged through the high or low side with the engine off. Tech B says the system can be charged thru the low side with the engine running. Who is right?
C. Charging the system can be performed through either the high or low side with the engine off. It must only be done through the high side with the engine on. This safety measure prevents high side pressure from entering the refrigerant containter and possibly causing an explosion.
An AC check has uncovered a discharge in the system and compressor damage. Tech A says that after repairs are made check the low pressure switch. Tech B says lubricating oil is carried by refrigerant thru the system. Who is right?
C. The purpose of the low pressure cut off switch is compressor protection. The compressor clutch circuit is opened if the pressure in the system drops too low. This would indicate that the system has lost some or all of its refrigerant charge. Since the lubricating oil is carried by refrigerant a loss could cause damage to the compressor if it were allowed to operate without sufficient lubrication.
When checking recycled refrigerant for excess air Tech A says the container must be stored at 65degrees F or above for 8 hours out of direct sulight before checking pressure. Tech B says that if the pressure is higher than the limit show for a given temp there is air in the tank.Who is right?
B. To purge the air, connect the tank to the R/R machine, and slowly vent the air vapor from the top of the container. Continue venting until the pressure falls below the limit shown on your chart. If the pressure inside still exceeds the pressure limit shown, recycle the entire contents. B is wrong because the container must be stored for 12 hours not eight.
Operation of the thermostatic switch depends on the temp of the
outside air
C. The thermostatic switch which is used to cycle the AC compressor on and off depends on the temp of the evaporator in order to operate.
All of the following are causes for fan clutch replacement except
oil film on the back of the clutch
no viscous dra
fan speed does not increase as engine warms
When engine is hot fan stops spinning only 2 seconds after shut down
D. A properly operating clutch should stop the fan from spinning within 2 seconds after a hot engine shut down. All the other answers are indications of a defective fan clutch.
Tech A says that an ambient temp switch protects the compressor from damage. Tech B says an ambient temp sensor provides input for the ATC system. Who is right?
C. In non ATC systems, the function of the ambient temp switch is to keep the compressor clutch from operating in cold ambient temps. This function protects the compressor from poor or no lubrication which could be the result of cold refrigerant oil. In ATC systems the ambient temp sensor senes ambient outside temp; as ambient or interior temps stray, the sensors pick up the change and the system adjusts the outlet duct temp accordingly to compensate for the temp changes.
If a capillary tube were to break at some point between its sensing bulb and the TXV what would happen to the valve?
The valve would stick open
The valve would stick closed
The valve would stick in whatever position it was in at the time of the break
No effect
B. Expansion valves are usually spring loaded devices with a diaphragm that is linked to a plunger. Without any pressure against the diapragm from the gas in the capillary tube, the spring inside the expansion valve would cause the valve to stick closed.
Customer complains of poor heat output. After checking hoses from heater core and finding them both to be hot Tech A says it could be a clogged heater core. Tech B says a misadjusted temp control cable would be the problem. Who is right?
B. If both hoses to the heater core are hot, coolant is circulating through the heater core. One hose that is significantly cooler than the other would indicate a clogged heater core. However, if the temp control cable is incorrectly adjusted, the temp blend door may not allow enough warm air to enter the passenger cabin for sufficient heating.
The R134A retrofit lable that is placed over the exisitng R12 reference labor must include all of the following information EXCEPT
Name and address of the company doing the retrofit
retrofit kit manufacturer name
date of the retrofit
type and amount of refrigerant and lubricant in the system
B. The parts used during a retrofit don't necessarily have to come from a kit, and even if they do, that information is not required on the retrofit label. All of the other information is required to be listed.
During diagnosis of an ATC system a trouble code is obtained that references the blend door feedback sensor. Tech A sasy the sensor should be replaced. Tech B says the sensor circuit should be tested. Who is right?
B. Fault codes usually only indicate which circuit the problem is in; they don't necessarily indicate which component in the circuit has failed. The problem could be caused by a loose connection, improper modification, or a broken wire, so perform a thorough inspection when diagnosing a malfunction. Ensure that all grounds are clean and making good contact. If basic mechanical and electrical checks fail to locate the problem, follow manufacturer electronic system test procedures.
A major cause for the depletion of the ozone has been attributed to
carbon monoxide fumes from auto exhaust
unburned hydrocarbon emissions from exhaust
release of cfc's in the atmosphere
all of the above
C. The release of CFCs into the atomosphere has been found to be a major cause of ozone layer depletion.
Which of the following sensors is not an NTC thermistor?
In vehicle sensor
ambient sensor
sunload sensor
engine coolant temp sensor
C. The sunload sensor is a photovoltaic diode. All other sensors are NTC thermistors.
A customer with an SATC equipped vehicle complains the car does not get cool enough on hot days. Tech A says the blend door actuator is probably malfunctioning. Tech B says the programmer is the problem. Who is right?
D. Both technicians are jumping to conclusions. To find the problem, a logical diagnostic procedure must be followed or parts may be replaced unnecessarily. This includes a preliminary inspection of the AC system and checking refrigerant pressures before condemning any part of the ATC system.
A compressor clutch will not engage. All of the following could be the cause except
a closed high perssure cutout switch
low refrigerant level
an open ambient temp switch
faulty compressor clutch coil
A. The high pressure cutout switch is normally closed. It opens the compressor clutch circuit when high side pressures are excessive in order to protect the compressor. All of the other answers would cause the clutch not to engage.
The inside of an EATC equipped vehicle never feels as cool as the temp setting. The AC system checks out OK including the sensors. Tech A says there could be an obstruction in the aspirator tube. Tech B says the aspirator tube could be disconnected from the duct. Who is right?
C. The in vehicletemp sensor is located in the aspirator which is located in the dash. The aspirator tube is connected to a heater-A/C duct. The air flowing in the duct past the tube creates a vacuum drawing in vehicle air past the sensor. If there is an obstruction in the aspirator tube or the tube is disconnected from the duct air will not be drawn past the sensor and it will not be able to accurately measure the temp inside the vehicle.
The ambient temp sensor in an EATC system is being tested. Tech A says the resistance of the sensor should increase as it heats. Tech B says that as the sensor resistance changes the computer reads the change as voltage drop across the sensor. Who is right?
B. The ambient temp sensor is an NTC thermistor. When an NTC thermistor is heated the resistance should drop and when cooled, resistance should increase.
At what % is refrigernat considered to be pure and safe for recovery?
C. Refrigerant is considered pure and safe for recovery if it at least 98% by weight of a single type of refrigerant. If it is less than 98% pure it should be considered contaminated and reclaimed or destroyed.
All of the following could cause lower than normal high side pressure EXCEPT
missing air dam
low refrigerant charge
worn compressor
restricted orifice tube
A. A lower than normal refrigerant charge and excessive internal wear would both cause the compressor to develop less discharge pressure. A restricted orifice tube would cause refrigerant flow through the system to be slowed. When the refrigerant spends more time in the evaporator its temperature and pressure are slightly reduced. A missing air dam would cause an air flow problem through the condenser and radiator. The reduced air flow and possible engine overheating would both cause higher than normal high side pressure.
2 techs are discussing an AC system retrofit. Tech A says that a high pressure cutout switch must be added. Tech B says the receiver drier should be replaced. Who is right?
C. If it does not have one, a high pressure cut out switch must be added to the system to stop compressor operation before the high side pressure reaches the point of opening the relief valve and releases refrigerant into the atomosphere. The receiver drier should be replaced because all refrigerants do not use the same type of dessicant.
A customer complains about a hiss coming from under the hood after turning off the car. Tech A says the noise is coming from the AC system and
a normal condition
system pressures equilizing
a refrigerant leak
both A and B
D. The hissing noise is normal and caused by high side pressure going through the refrigerant metering device as system pressures equalize.
A customer complains of low air flow through the instrument panel duct outlets. Which of the following could be the cause?
Faulty blower motor
clogged passenger compartment air filter
stuck mode door
all of the above
D. A mode door stuck between 2 positions would create the impression of reduced air flow because the available air would be routed to 2 places instead of one.
All of the following are classifications of anti freeze except
inorganic additive technology IAT
organic additive technology OAT
Hybrid inorganic additive technology HIAT
hybrid organic additve technology HOAT
vehicles with dual zone climate control have a separate _______ for the passenger side of the vehicle.
mode door
blend door
heater core
evaporator core
B. Vehicles with Dual Zone climate control have a separate blend door for the passenger side.
When using an electronic refrigerant leak detector all of the following should be obsereved EXCEPT

leak detectors are very sensitive to many types of gases. If the area is conaminated w refrigerant or other gases, use a fan or compressed air to blow the excess refrigerant away
pass the probe around the top of the componets as refrigerant tends to rise
dont move the probe faster than 1in per second
never allow the probe to contact any surface to prevent contamination of the sensor tip.
B make sure you pass the probe around the bottom of components and hoses, as refrigerant is heavier thank air and tends to settle.
Tech A says that mineral deposits can restrict air flow through the radiator. Tech B says that internal restrictions in the radiator can be detected from the outside. Who is right?
B. A is wrong because mineral deposits can restrict coolant flow inside the radiator, not air flow through the radiator. B is right because an infared surface thermometer can be used to scan the surface of the radiator. When at op temp, the radiator should be warmest near the inlet and gradually cool near the outlet.
A typical refrigerant identifier can detect all of the following except:
D. Systems that use R744 refrigerant, which is pure CO2, are still under development. Typical refrigerant identifiers that are available can detect R12, R134a, R22, air and hydrocarbons.