1060 weekE (CH49)

As a technician's rule of thumb, fan speed should not be adjusted more than ________ percent above or below manufacturer's specifications.

10

Normally, a split AC system that uses a fixed metering device can safely operate at temperatures:

Above 65°F.

How does the refrigerant charge affect a system's subcooling?

Adding refrigerant increases the system subcooling

Three general areas of problems in air-conditioning systems include electrical problems, mechanical problems, and:

Airflow problems

A split-system air conditioner that does not operate at all most likely has:

An electrical problem.

The evaporator coil operating temperature for a system with a 20°F split, 85°F return air, and 71°F supply air is:

COT = ((85°F - 71°F)/2) - 20 = 58°F.

How can a technician check to see if the coil and condensing unit on an AC split system are matched?

Call the equipment supplier and provide the system model numbers.

The expected temperature drop through a direct expansion evaporator coil:

Can be determined with a chart supplied by the coil manufacturer.

The first electrical checks of a system that is not operating generally involve:

Checking the power circuit to the equipment.

The most common cause of airflow-related problems in air-conditioning units is:

Dirty air filters.

The majority of problems with residential air-conditioning systems are due to:

Electrical problems.

Fault isolation diagrams and troubleshooting tables help the technician locate problems through the process of:

Elimination

What is a common symptom of a severely restricted filter drier?

Frost forming on the outlet

Symptoms of an inefficient compressor include:

High suction pressure, low discharge pressure, and low amp draw.

If an electrical load in a split-system air conditioner is not working, the technician must determine if the problem is:

In the load itself or in the switches that control the load.

Electronic controls on air-conditioning systems typically report faults by:

Indicating a fault code.

When working on a type of system that you have never seen before, you should:

Locate the manufacturer's troubleshooting guide.

The most common airflow problem experienced on air-conditioning systems is:

Low airflow caused by dirty or plugged air filters.

When an air-cooled split system operates at low ambient temperatures:

Low ambient controls are necessary for safe operation.

The manufacturer's data on a split AC system indicates that the normal temperature drop should be 15°F at the current operating conditions. If the evaporator entering air temperature is 80°F and the leaving air temperature is 55°F, the technician knows that the system:

Most likely has low air flow because of the higher-than-normal temperature drop.

The refrigerant condensing temperature for an air-cooled system having a 20°F split is:

RCT = 95°F + 20°F = 115°F.

Adding a little extra refrigerant over the amount recommended by the manufacturer:

Reduces both system capacity and efficiency.

A high temperature differential (more than 2 degrees) between return air temperature at the grille and the return air temperature at the unit indicates:

Return air leakage.

When the liquid line is restricted, the supply of refrigerant to the metering device is reduced. What is the effect on suction pressure and superheat?

Suction pressure goes down and superheat increases

If an air-conditioning system is operating with an 80°F return air temperature and a 50°F supply air temperature:

The large temperature drop indicates the airflow is less than required.

How is the subcooling of an air-conditioning system affected by a restriction in the liquid line?

The subcooling will be above normal.

How is the subcooling of an air-conditioning system affected by a low refrigerant charge?

The subcooling will be below normal.

When a split AC system using a capillary tube is overcharged:

The superheat will decrease.

What is meant by the coil split?

The temperature difference between the coil operating temperature and the air passing over the coil

When ohming components on the system, it is important to:

Turn off the power to the unit.

A common cause of poor airflow is:

Unusual airflow restrictions in the duct.

The suction pressure on a split AC system that is running with an excessive evaporator heat load:

Will be higher than normal.

When charging a capillary tube system that holds 100 oz., the charge must be:

Within 5 percent, between 95 and 105 oz.

Manufacturer's troubleshooting charts typically ask:

Yes/no questions to determine the cause.