There's a growling or rumbling noise at the A/C compressor, with the compressor engaged or disengaged.
Technician A says: The compressor bearing is defective.
Technician B says: The clutch bearing is defective. Who's right?
B. B only.
All of the following are good methods of verifying that an engine thermostat opens EXCEPT:
D. Watching the surge tank.
With the HVAC system in DEFROST mode, the blower on HIGH and the temperature control on COLD, the bottom of the windshield fogs up on the outside because.
A. The cold windshield causes moisture to condense from the outside air.
The A/C high pressure relief vale shows evidence of slight oil leakage.
Technician A says: you must replace the valve and repair the leak.
Technician B says: If the valve is leaking just a little oil and not refrigerant, repair is not necessary. Who's right?
A. A only
Technician A says: That an ATC control panel can be reprogrammed using a hand held digital diagnostic tool.
Technician B says: That a hand held digital diagnostic tool can be used to help diagnose ATC system failure. Who's right?
B. B only.
An air conditioning compressor has a growling noise which occurs only when the compressor clutch is engaged. Which of these could be the cause?
D. A defective internal compressor bearing.
ATC systems may use any of the following sensors EXCEPT:
C. A manifold pressure sensor.
During normal A/C operation a loud hissing noise is heard and a cloud of vapor is discharged from under the vehicle.
Technician A says: that excessive high-side pressure that caused the pressure relief valve on the A/C compressor to trip may have been the result of a defective engine cooling fan clutch.
Technician B says: The relief valve may have tripped due to a defective shutter solenoid. Who's right?
C. Both A and B.
Before a portable container is used to transfer recycled R-12, it must be evacuated to at least:
B. 27 in. Hg.
When attempting to verify a leaking evaporator core, the Technician is LEAST-LIKELY to sense refrigerant with the detector probe:
D. Over the expansion valve.
Technician A says: That deformed or improperly aligned condenser mounting insulators will damage the A/C compressor.
Technician B says: That deformed or improperly aligned condenser mounting insulators could damage the condenser and refrigerant lines. Who's right?
B. B only.
Technician A says: That an ATC control panel can be reprogrammed using a hand held digital diagnostic tool.
Technician B says: That a hand held digital diagnostic tool can be used to help diagnose ATC system failure. who's right?
B. B only.
The A/C High pressure relief valve shows evidence of slight oil leakage.
Technician A says: you must replace the valve and repair the leak.
Technician B says: if the valve is leaking just a little oil and not refrigerantm repair is not necessary. who's right?
A. A only
C. Both A and B
D. Neither A nor B
A. A only.
A coolant temperature sensor is classified as NTC negative temperature coefficient.
Technician A says: this is a thermistor in which internal resistance decreases in proportion to temperature rise.
Technician B says: that in most truck engine cooling systems, a thermistor is supplied with v-batt (battery voltage) and returns a portion of it as a signal. who's right?
A. Technician A
Raising the pressure in the cooling system:
D. Raises the boiling point of the coolant.
Technician A says: when ever there are bubbles or foam in the sight glass it indicates the refrigerant charge is low and that air has entered the system.
Technician B says: a sight glass is not an accurate indicator of moisture in the system. who's right?
B. B only.
Technician A says: when installing a new or rebuild compressor you should first turn it over by hand and drain any oil shipped with the compressor, and then install the correct amount of the specified oil before installing it.
Technician B says: some compressors are shipped with out oil. who's right?
C. Both A and B.
What is the function of the STV, POA, ETR, and EPR valves:
B. Control evaporator pressure.
Technician A says: if there is no output from the blower motor switch, you replace the switch.
Technician B says: the feedback from the blower motor resistor could be the cause. who's right?
D. Neither A nor B.
All of these statements about cooling system service are true EXCEPT:
C. When the cooling system pressure is increased, the boiling point is decreased.
The recommended tool for diagnosing electronic sensors and actuators in and ATC system is:
C. a digital diagnostic reader ( DDR )
Poor cooling from the AC system that uses a STV valve can be caused by all of the following EXCEPT:
A. the fan clutch always engaged.
What is the source of most non-condensable gases in refrigerant?
A. Air
Acid: is wrong because any acids that form int AC system are created due to moisture and corrosion and are usually in a liquid state
Moisture: is wrong because moisture in the AC system only evaporates when the system is drawn under a vacuum, and is therefore normally in a liquid state.
Oil: is wrong because refrigeration oil is normally in a liquid state.
Each of these is an indication that the thermostat has open EXCEPT:
C. the lower radiator hose is hot.
During an HVAC performance test, the technician notices that the AC compressor outlet is nearly as hot as the upper radiator hose. Technician A says that this is a normal condition.
Technician B says that the system is overcharged. Who's right?
A. A only
The LEAST-Likely cause of the high-pressure relief valve tripping open is:
D. a defective AC compressor.
The test for non-condesable cases in recovered/recycled refrigerant involves:
A. comparing the pressure of the recovered refrigerant in the container to the theoretical pressure of pure refrigerant at a given temperature.
B. comparing the atmospheric pressure to the relative humidity.
C. comparing the container pressure with the size of the container.
D. testing the refrigerant with a halogen leak detector.
Answer A. is correct because comparing the pressure of recovered refrigerant to the theoretical pressure of pure refrigerant at a given temperature is the best method of testing for non- condesable gases in refrigerant.
B. is wrong because pressure cannot be compared to humidity.
C. is wrong because pressure cannot be compared to volume.
D. is wrong because a halogen detector cannot be used to check for non-condensable gases.
Technician A says that as specified by SAEJ1991, recycled refrigerant cannot contain more than 152 ppm moisture contaminants by weight.
Technician B says 330 ppm non-condensable gases (air) by weight. who's right?
A. A only
B. B only
C. Both A and B
D. Neither A nor B
A. is wrong because recycled refrigerant must contain less than 15 ppm of moisture and B is also correct.
B. is wrong because recycled refrigerant must contain less that 330 ppm of non-condensable gases and A. is also correct.
C. is correct because both technicians are right.
D. is wrong because neither technician is wrong.
A typical ATC system will delay motor operation until coolant temperature reaches:
B. 120 F. because blower operation is delayed to prevent air from entering the cab at an uncomfortable temperature.
Approximately how much refrigerant oil must be added to a newly replaced evaporator core?
A. is correct. most manufactures recommend 3 oz.
A. is wrong because you have to add oil.
C. is wrong because 9 ounces would cause excessive system oil.
D. is wrong because entire system contains about 14-1/2 ounces of oil.
Technician A says that many trucks are programmed with engine protection strategy to warn the driver if coolant level and temperature are not within preset parameters.
Technician B says that imminent engine shut down can be overridden for a brief period after the alarm to allow the driver to move the vehicle to a safe place. who's right?
C. Both A and B.
A. is good choice but wrong, because most trucks are also equipped with an override switch.
B. is also a good choice but wrong, because many trucks are also equipped with a shutdown alarm.
D. wrong because both techs are right.
Which of the following is the least likely cause of a shutter system that will not close completely?
B. A blown shutter fuse is the least likely cause since most shutter systems are air operated not electrical.
What is the odor of R-134a. and R-12?
R-134a has a faint ether-like odor
R-12 is odorless
what does a typical heavy duty truck cooling system operate at?
D. anywhere from 10 to 15 psi
How much refrigerant oil does a typical condensor hold?
Recycled: refrigerant that has been filtered to remove contaminants and oil.
Recovered: refrigerant that has been removed and stored in an external container from a system.
Reclaimed: refrigerant that has also been reprocessed to return it to new product quality.
Refined: it's a process that is not used with refrigerants
If R-12 comes in contact with flame:
A. it will form phosgene gas.
A. wrong: it is not flamable
B. wrong: it is toxic
C. wrong: it does not turn to chlorine gas
On a cycling clutch AC system, the low side reading is too high and the high side reading is too low.
Technician A says: that the compressor may have an internal leak.
Technician B says: that an overcharge of refrigerant oil is a possible cause. Who's right?
A. A only is correct because internal compressor leaks could cause these symptoms.
Purging a system too fast will result in:
A. is correct because oil will atomise and leave the system with the refrigerant.
In truck AC systems, evaporator core icing can be prevented by any of the following EXCEPT:
C. is correct because a low pressure switch is there to protect the compressor in case of low refrigerant
An AC system with excessive high side pressure could be the result of all the following EXCEPT: '
C. is correct because blockage in the orifice tube will cause low high side pressure.
A compressor cycling on and off too fast is one symptom of:
A. is correct because a low refrigerant charge will cause the clutch to cycle more frequent than normal.
Note: an overcharged system will most likely cause the compressor to remain engaged.
which of these AC gauge set readings would most likely indicate an AC compressor that is worn out?
A. High side pressure too low and low side pressure too highB. No pressure on either gauge
C. Both gauges read pressure that is too low
D. a low refrigerant charge
A. is correct. because a weak compressor would be unable to create very much pressure difference between high and low side.
which of the following modes will provide least effective windshield defrosting in the defrost mode?
B. is correct because 50% output is the least effective defrosting
Note: the most effective modes to provide defrosting is 85%
If the expansion valve is not opening, the system will show which of the following pressure combination on a manifold gauge set:
D. Answer A is correct because if the expansion valve is stuck closed, the low side of the system will be pulled down into a vacuum and the compressor will not be able to sufficiently pressurize the high side.
If the blower operates in all speeds except medium, which of the following problems is the most-likely cause?
A. Is correct. A defective blower switch
B. is wrong because an intermittent short will affect all blower speeds.
C. is wrong because a faulty relay would only affect high-blower speeds.
D. is wrong because a loose connector will affect all blower speeds
Technician A says: that current fuel-fired heaters are electronically controlled and cycle according to temperature. Technician B says: that fuel-fired heaters burn less fuel than idling the engine. who's right?
C. Answer C is correct because fuel-fired heaters are electronically controlled and burn less fuel than running the engine at idle.
A. is wrong, good choice but both techs are right
B. is wrong, good choice but both techs are right
D. is wrong because both techs are right
While conducting a performance test on a semi-automatic HVAC system, a tech finds that only a small amoundt of air is directed to the windshield in DEFROST mode. The Most-likely cause of this problem is:
D. is correct because an improperly adjusted cable could affect the amount of air that is directed toward the windshield.
The compressor discharge valve is designed to:
C. is correct. open after vaporized refrigerant is compressed, allowing the refrigerant to move to the condenser.
Tech A says: that the evaporator must be removed from the vehicle if the presence of evaporator lubricant is to be checked. Tech B says: that the refrigeration oil is distributed throughout the AC system. who's right?
B. only. oil gets distributed throughout the system
What oil is used on 134A
PAG oil
A gasoline engine in a school bus with indirect port fuel injector and air conditioning has an excessively rich air-fuel ratio. this problem could be caused by which of these items?
B. is correct because a stuck open thermostat will make the engine run cool sending cold engine message to the ecm resulting in rich air fuel mixture.
Which of the following tests or instruments would provide the most accurate measurement of coolant antifreeze protection?
C. Refractometer
All of these facts about a computer controlled AC system are correct EXCEPT:
C. is correct because DTC represent fault in a specific system and not in a specific component
In a normal operating AC system the low-side pressure varies between:
and the high pressure between:
low: 20 and 45
High: 120 and 210
AC pressure diagnosis:
Low low-side and Low high-side:
- restricted line from condenser to evaporator
- TXV stuck closed and clogged orifice tube
- obstruction in the suction line
- low refrigerant charge
AC pressure diagnosis:
High high- side and High low-side:
- air or moisture in refrigerant
- High engine coolant temp
- restricted condenser flow
-TXV valve stuck open
- refrigerant over charge
AC pressure diagnosis:
Low low-side and High high-side:
- restrictive evaporator air flow
AC pressure diagnosis:
High low-side and Low high-side:
- internal compressor damage