Ch59 Servicing Heating and AC Systems

Vacuum gauge

A gauge designed to read negative pressure or vacuum.

Following a repair, the AC system should be

Evacuated via an AC machine or AC manifold gauges and a vacuum pump.

A performance test involves

External cooling for the condenser, running the engine between 1100 and 1500 rpm, placing the AC on max cold, the fan on high, and measuring the duct temperature, and then comparing the duct temperature to a system performance chart from the manufacturer.

State of charge

The amount of refrigerant in a system compared to how much should be in it.

Charge

The amount of refrigerant present in the system or the process of installing refrigerant in the system.

The one rule for diagnosis of poor quality refrigerant is

"When in doubt, remove it out."

1. Technician A states that the wider the gap on an AC clutch, the greater the electrical resistance measurement is observed when checking the windings. Technician B states that a wide clutch gap causes the compressor to remain engaged. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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10. Technician A says if moisture enters the AC system, acid is created. Technician B says evacuating an AC system boils away moisture, which is removed from the system as a gas. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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2. Technician A states that an AC performance test usually requires that an auxiliary condenser fan be used during the test. Technician B states that a performance test shows if the AC system is contaminated with sealer. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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2. Which of the following is the first step in the AC system inspection and diagnostic process? A. System pressure test. B. Diagnosis of faults C. Performance testing D. Check for codes in computer.

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3. Technician A states that refrigerant in a vehicle should be identified before recovering the refrigerant. Technician B says a sealant detector should be used to check refrigerant before it is recovered. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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3. Which of the following is correct regarding refrigerant identification? A. The identifier connects to the low-side center-port of the manifold gauge set and samples the refrigerant. B. The only way to determine the type of refrigerant in a system is with the use of a sealant detector. C. The identifier reports the concentration of R-134a in a percentage. D. Concentration of refrigerant gas is performed before checking for the presence of AC system sealant.

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4. Technician A says when evacuating an AC system, the vacuum should be maintained for approximately 10 minutes after the system reaches the boiling point pressure of water. Technician B says the primary purpose of evacuating an AC system is to remove any air from the system. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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4. Which of the following is found on the AC information decal? A. The volume of refrigerant B. The weight of. A full refrigerant charge. C. The viscosity of system oil D. Maximum safe operating pressure

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5. Technician A says the AC system should be flushed if the compressor came apart. Technician B says the system should be flushed if the oil is contaminated. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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5. Which of the following is correct concerning the state of refrigerant charge? A. State of charge in the AC system refers to the amount of refrigerant in the system compared to how much should be in the system. B. State of charge is best measured by removing all of the refrigerant and recharging the system with the proper amount of refrigerant, as specified by the service information. C. An overcharged AC system will cool better but use more energy. D. An undercharged AC system will operate more quietly than a properly charged system.

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6. Technician A says when using pressurized nitrogen to locate a leak, an electronic detector should be used. Technician B says electronic detectors are used when the system has at least a minimal refrigerant charge. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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6. Which fo the following is correct concerning a refrigerant undercharge of the AC system. A. Undercharging the AC system increases high-side pressure but has lower low-side pressure readings. B. Both the low- and high-side gauge pressure indicate higher than normal operating pressures. C. Both the low- and high-side pressure readings are below normal. D. An undercharge condition can only be determined by measuring air vent temperatures.

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7. Technician A says micron measurement units are a much more accurate unit of measuring vacuum than inches of mercury (Hg). Technician B says micron measurement units are provided on most manifold gauge sets how side gauge. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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8. Technician A says to determine how much refrigerant is needed in a system, you must refer to identifying labels on the vehicle or the service manual. Technician B says to determine the amount of refrigerant is needed, you just charge the system until the pressures reach normal values. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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9. Technician A says when removing any part of an AC system, the oil should be drained from it and measured so that the same amount can be reinstalled. Technician B says oil should only be in the compressor, and if any oil is found in any other components, it means the receiver dryer is faulty. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B

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Micron gauge

A device designed to measure the amount of vacuum very precisely.

Muffler

A device designed to measure the amount of vacuum very precisely.

Accumulator

A device placed between the evaporator and the compressor to collect liquid refrigerant and prevent it from entering the compressor. See also hydraulic accumulator.

Oiler

A device used to add oil to the AC system.

AC machine

A machine designed to recover recycle, evacuate, leak test, and recharge (R/R/R) the AC system.

PT chart

A pressure-temperature chart that shows the relationship between AC pressures and evaporator temperature.

Vacuum pump

A pump used to evacuate the AC system of air and put the system into a deep vacuum or low pressure to remove moisture.

Manifold gauge set

A set of calibrated gauges for measuring high and low pressure AC gases that can show pressure and vacuum readings for use with AC systems.

Reclaim/recycle machine

An AC machine designed to remove and recycle refrigerant for reuse.

AC compressor clutch

An engagement device connected to the compressor crankshaft to lock the crankshaft with a belt-driven pulley.

Drive pulley

Any belt-driven pulley used to power an accessory, such as power steering or the AC compressor.

1. Compared to a medium-sized house, what capacity will a typical transit bus AC system have? A. Four to six times more than a house. B. 20 to 30 times more than a house. C. One-third less than a house. D. The same capacity as a house.

B. Transit buses have high-demand HVAC requirements, including an air flow of between 2500 and 3500 cam (71 and 99 cubic meter/minute) and the cooling capacity of 20 to 30 times that of a medium-sized home AC unit. P1701

AC performance testing should be done

Before and after repair.

Clearing the drain hose can

Clear up odors. If this does not work, an anti-odor kit may be required.

The air distribution system is

Designed to circulate air through the heating and cooling system, then into the passenger cabin.

Refrigerant identifiers

Devices used to check for impurities in the AC gas

Technicians must be

EPA 609 certified to handle refrigerants.

Methods of leak testing are

Electronic detector testing, date testing, and nitrogen testing.

Methods of leak testing are

Electronic detector testing, dye testing, and nitrogen testing.

The AC system should be flushed

If the compressor internally disintegrates, the desiccant bag breaks open, or the oil is contaminated.

Confirm the quality and type of refrigerant

In the system by using a refrigerant identifier.

An undercharged AC system contains

Less refrigerant than the system calls for.

Pressure transients

Minor fluctuations on the gauges that may indicate a problem.

Performance testing of the AC system is

One of the first steps in diagnosis

Overcharging

Overfilling of the AC system; may result in poor cooling or mechanical failure of the system.

Servicing the AC system involves

Performance testing the system, diagnosing any issues, leak testing, identifying the refrigerant, reclaiming the refrigerant, performing any repairs, evacuating the system, recharging, retesting for leaks, and performance testing.

AC system inspection should include

Possible condenser airflow restrictions, evaporator housing water drain, air filter, hoses and belts, cooling fan, fan clutch, fan shroud, and heater control valves.

Steps to the diagnosis and repair of AC systems are

Pretest and inspection, leak test, reclaiming refrigerant, problem repair, evacuation, charging, and post testing.

Recovering

See reclaiming

The compressor is

The most common source of abnormal noises arising from the ac

Performance testing

The process of recreating a driving situation to inspect AC performance and vent temperatures.

Reclaiming

The process of removing refrigerant from the AC system by using an AC machine; also called refrigerant recovery machine.

Any time the AC system is opened,

The refrigerant must be recovered (reclaimed).

Tools needed

To maintain and repair AC systems include: sealant detector, reclaim/recycle machine, refrigerant identifiers, pressure gauge sets, AC machine, anemometer, retrofit kit, pressure-temperature chart, vacuum pump, electronic leak detector, dye leak detector, oiler, vacuum gauge, micron gauge, and line wrench.

Problems with AC system performance may be due

To system leaks, compressor failure, or system blockages.

Charge refers

To the amount of of refrigerant in the AC system.

If the high-side pressures are

Too high and the system is not cooling well, check the air flow through the condenser.

Ac systems are equipped

With protective devices designed to shut down the system if refrigerant pressures are too high or low.

Identifying refrigerant helps

avoid mixing refrigerants, which cannot be reused and must be stored separately.

Any time the AC system is opened, the refrigerant must be

recovered (reclaimed).