Model number

BTB390A 567CO36RCU 38CC042-1 CM48-42C

Btu/hour

30,000 36,000 42,000 48,000

Tons

contain the refrigerant that cycles between the two units. (See FIG. 17-2.) The diameters of the two pipes are different—one pipe is the size of a pencil, the other the size of a broom handle. The small pipe (pencil size) is the liquid line; it carries the high-pressure liquid refrigerant from the condenser to the expansion valve. The larger pipe (broom-handle size) is the suction line; it carries low-pressure refrigerant gas from the evaporator coil to the compressor. The suction line should be insulated. Usually it is covered with black foam-rubber type of insulation.

Inspection procedure Whether the air-conditioning system can be checked operationally depends on the outside air temperature. Most manufacturers do not recommend turning on the system at temperatures below 60° F because of the possibility of damage to the compressor. If the outside temperature is below 60° F during your inspec tion, do not start up the air conditioner. If the system cannot be checked prior to purchasing the house, the seller should provide you with a guarantee of its operational integrity. If the temperature is above 60° F during your inspection, walk over to the compressor and have someone turn down the thermostat that controls the air conditioner so that the system will begin to operate.

Compressor The compressor is the most important part of any air-conditioning system and the most costly to replace. Its projected life is about eight to ten years, although units have been known to last over fifteen years. In areas of the sunbelt with long air-conditioning seasons, the projected life will be somewhat less. After the system has been turned on, listen for any unusual sounds. The compressor should start up smoothly. A straining, grunting, groaning, or squealing noise indicates a problem condition that should be checked and

Schematic Diagram Split
Fig. 17-2. Schematic diagram of a split air-conditioning system. The compressor-condenser is located outside the house, and the cooling coil is inside the house (usually in the furnace plenum or attic).

corrected by a competent service organization. Shut the unit off and note the condition on your worksheet. Once the compressor starts up smoothly, it should then operate continuously without any noise (except a low hum) or squeaks. The compressor should not operate in short cycles (on and off repeatedly). If this occurs, there is a problem condition and the unit should be shut down.

When the air-conditioning system is turned on, the fan associated with the condenser should begin to operate at the same time as the compressor. Look inside the unit to see if the fan is turning. If the interior portion is not visible and you cannot see whether the fan is operating, place your hand over the unit. Air rushing over your hand is an indication that it is operating. After the system has been operational for about fifteen minutes, the air being discharged through the condensing coil should be warm. This air is removing the heat that has been generated during the compression of the refrigerant. Air that is not warm is usually an indication that the compressor is not operating properly, a condition that should also be checked by a competent service company.

After the system has been operational for about fifteen minutes, look at the low-pressure refrigerant line (the pipe about the size of a broom handle). Usually the pipe is covered with insulation. If a section of the pipe is exposed, grab it with your hand. If the compressor is working properly and there is an adequate refrigerant charge, the pipe will be quite cool to the touch. On many occasions, the pipe and end fittings will be "sweating" as a result of condensation. This is a normal operating condition. However, a low-pressure line covered with frost usually indicates a deficiency in refrigerant. Even though cooling can be obtained with an air-conditioning system that is deficient in refrigerant, the efficiency of the system is greatly reduced.

Occasionally you will find a sight glass on the small-diameter refrigerant line. The sight glass is a small device installed directly into the high-pressure liquid refrigerant line that allows the homeowner to see whether there is a problem with the flow of the liquid refrigerant. The refrigerant is colorless, and if the system is operating properly, nothing unusual will be noted when looking at the sight glass. However, when the system is low in refrigerant, bubbles will show up in the liquid as it passes under the glass. Record it on your worksheet.

The location of the compressor-condenser is important for efficient operation. (See FIG. 17-3.) The compressor should be located where it will receive a minimum of direct sunlight, since the cooler the air flowing across the condenser, the more efficient the cycle. See if the compressor is positioned so that the condenser air intake is at least 12 inches away from any obstruction or dense shrubbery. If it isn't, there will not be an adequate airflow for condenser cooling.

The compressor-condenser can be a noisy piece of equipment and should be vibration-mounted on a concrete slab or precast concrete

Refrigerant Line Fracture
Fig. 17-3. Typical compressor-condenser for a split air-conditioning system. Airflow through unit must be unobstructed.

blocks that will not settle. The unit should be level. Excessive uneven settlement can cause fractures in refrigerant-line fittings and thereby allow the refrigerant to escape.

Look for an electrical disconnect switch on the exterior wall near the compressor. The purpose of this switch is to allow the maintenance man to disconnect the unit so that if someone in the house unknowingly turns the thermostat down, the unit will not be activated while he is making repairs. The absence of a disconnect switch should be recorded on your worksheet. The overall compressor-condenser unit should be checked to see whether it is in need of a cleaning. These units require periodic cleaning because leaves, seed pods, twigs, and dust tend to clog the condenser, thus restricting the airflow. The condenser has fins like an automobile radiator's, which can clog easily.

The condenser discussed above is air-cooled. On occasion, you might see a condenser that is water-cooled. A water-cooled unit can be located inside the structure since it does not require outside air. These condensers are generally not used for residential structures because they are quite wasteful and costly to operate. To cool the condenser adequately, cold water flows through a jacket around the coils absorbing heat and is then directed into a sink or floor drain. If the central air-conditioning system operates for twelve hours a day, this type of system can waste several thousand gallons of water a day. If you find this type of condenser in the air-conditioning system, you should consider its replacement.

In large air-conditioning systems such as those found in apartment buildings, water-cooled condensers are not wasteful or costly to operate because the cooling water is recirculated. After the water absorbs heat in the condenser, it is pumped up to a cooling tower, often located on the roof, where it loses its heat and is then recirculated to the condenser.

Evaporator After checking the compressor-condenser, you should inspect the evaporator unit, commonly called the cooling coil. The evaporator will usually be located in the attic or the basement. When the unit is located in the attic, you will often find the refrigerant lines from the compressor running up along the outside of the structure and entering the building at the attic level. When the evaporator coil is located in the basement, either as a separate unit or in the furnace plenum, the refrigerant lines from the compressor are short and run directly into the structure. If possible, the evaporator coil should be observed after the unit has been operational for about thirty minutes. The coil might not always be accessible because it may be covered with a sheet-metal casing that cannot be easily disassembled. If the evaporator is accessible, look at the coil and the associated refrigerant tubing. The evaporator is used to cool and dehumidify the circulating air. If you notice a frosting condition (a buildup of ice) on portions of the coil and refrigerant tubing rather than dripping water, the system is not operating properly. The frosting is usually the result of an insufficient airflow through the evaporator coil or an inadequate amount of refrigerant in the system. This condition should be indicated on your worksheet.

Furnace-mounted evaporator When the house is heated by forced warm air, the most common location for the evaporator is in the furnace plenum. A furnace-mounted unit takes advantage of the ducts that have been installed for heating the house and also uses the heating-system blower to circulate the cool air.

You can tell if the evaporator coil is located inside the furnace plenum by whether there are refrigerant lines entering the sheet-metal casing of the plenum. The refrigerant lines inside the casing are connected directly to the evaporator coil. The most common type of coil that is found in a furnace plenum is a two-section design, an A-coil (because of its shape).

Sometimes an inclined or horizontal coil is used. (See FIG. 17-4.)

Below the evaporator coil is a pan that collects the water condensing out of the circulating air. The water is then removed by means of a plastic drain line that will be visible when looking at the furnace plenum. Look for it. Depending on the location of the furnace, the condensate drain line will run to a nearby sink where the condensate drips down the drain or will run through the foundation wall, where the condensate drips on the outside. When the condensate drain line is extended through the foundation wall, there should be a splash plate below the end of the pipe so that the dripping water can be directed away from the foundation.

Sometimes the condensate drain line runs from the furnace down to a small hole in the floor slab. The condensate trickling out of the drain line accumulates below the slab. This

Furnace Condensate Trap
Fig. 17-4. Evaporator (cooling) coil mounted in furnace plenum.

method of removing the condensate is not very desirable in those areas where the water will not readily drain because of a high water table or a high clay content in the soil. Even though the amount of water discharging from the condensate drain is small, the introduction of additional water could aggravate a condition that makes the lower level of the structure vulnerable to water seepage.

The condensate drain line should terminate at the plenum with a U-shaped trap. Since the condensate drain line is an open pipe leading directly into the cooling coil, the trap (which is partially filled with water) prevents any of the cool air from escaping through the pipe. Look for a trap. If it is missing, record that on your worksheet.

Occasionally the condensate drain discharges into a small rectangular box located near the furnace. This box is the reservoir for a lift pump. The purpose of the pump is to lift the condensate to a level where it can then flow to any desired location. Without a pump, it is often necessary to position the drain line so that it blocks a portion of the room or interferes with foot traffic. Check the pump's operation. These pumps have a float control that is activated when the water reaches a preset level. If there is only a small amount of water in the reservoir, the pump can be checked by pouring water from a glass into the reservoir. A malfunctioning pump should be recorded on your worksheet.

Now look at the overall furnace plenum around the evaporator coil. Rust and mineral deposits indicate a past or present problem in condensate removal. Water overflowing the condensate drain pan can damage the heat exchanger below. If you see this condition, you should have the furnace heat exchanger checked by a heating contractor for signs of deterioration. (See chapter 14.)

When the evaporator coil is located inside the furnace plenum, the blower for the heating system is also used as the blower for circulating the cool air. Because cool air is heavier than warm air, when the blower is used for air-conditioning, it should operate at a higher speed. Most often, however, the furnace is equipped with a one-speed motor. Consequently, the air-conditioning system is often not as effective as it might be. A pair of double-or triple-sheaved hubs can be installed to allow multispeed operation. When the blower is turned off by the master switch, check the tension in the fan belt. There should be no excessive slack. Press the belt midway between the pulleys. If the belt gives more than 34 inch to an inch, it is too loose, and adjustment is needed. When the blower is operating, listen for any unusual noises or vibrations. They should be recorded on your worksheet. You might also ask the owner when the unit was last serviced—there is no substitute for periodic maintenance.

Blower coil When the evaporator coil is housed in a separate casing that contains a blower for circulating the cool air, the coil is commonly referred to as a blower coil. Most often, the blower coil is located in the attic. However, it can be located in a closet or in the basement. The blower coil should be vibration-mounted to prevent the noise of the blower unit from being transmitted into the living area. Vibration mounting can be achieved by placing the unit on rubber, cork, or styrofoam pads. (See FIG. 17-5.) The vibrations might also be isolated in the attic by suspending the unit from the roof rafters.

The base of the blower coil is basically a condensate collection pan. The accumulated condensate is removed by means of a drain line that will extend through the exterior wall, terminating on the outside, or extend through the lower portion of the roof, terminating in the gutter. Sometimes the condensate drain line terminates in the plumbing vent stack located in the attic. (See FIG. 17-6.) In many

Condensation Drain Attic Unit
Fig. 17-5. Attic-mounted blower coil. Unit is resting on a styrofoam pad to minimize vibrations. Below the unit is an auxiliary condensate drain pan and associated drain line. Note that the main condensate drain line does not have a U-shaped trap.

communities, this type of termination is not permitted because it is not in compliance with the plumbing code. If the drain terminates in the vent stack, record that on your worksheet. The legality of this type of connection should then be verified with the local building department.

The purpose of the vent stack is to channel sewer gases in the plumbing system to the outside. If the condensate drain line is connected to the vent stack and there is no trap on the drain line, the sewer gases may back up into the condensate drain line, enter the blower coil, and be circulated throughout the house. The condensate drain line should have a U-shaped trap near its connection to the blower-coil housing. On many installations, this trap is omitted. Look for it. If it is missing, one should be installed.

When the blower coil is located in the attic, certain steps must be taken to prevent cosmetic damage to the ceiling below in the event of a blockage in the main condensate

Condensate Line Into Main Sewer Line
Fig. 17-6. Air-conditioning condensate drain line terminating in plumbing vent stack. In many communities, this type of termination does not comply with the plumbing code.

drain line. Some blower-coil housings have a fitting for an auxiliary drain line that is located just above the main condensate drain fitting. If the main drain becomes clogged, the level of the condensate will rise and be drawn off by the auxiliary drain.

For those blower coils that do not have a fitting in the housing for an auxiliary drain line, there should be an auxiliary drain pan below the unit. The auxiliary pan will collect any condensate that overflows from the main pan when there is a blockage in the main drain line. Look for an auxiliary drain pan. In some parts of the country auxiliary drain pans are installed when the blower coil is located over any furred space, even when the blower housing has an auxiliary drain fitting. Record the absence of one on your worksheet. Unfortunately, many air-conditioning contractors do not install the auxiliary drain or drain pan. Because rising costs make it difficult to remain competitive, they cut costs wherever they can.

The auxiliary drain pan must have a separate drain line that discharges to the outside. It should not be connected to the main drain line. (See FIG. 17-7.) If it is, it reflects poor-quality workmanship; if the main drain line becomes clogged near the discharge end, the auxiliary drain line will also not function.

If the evaporator coil is accessible, it should be inspected for frost buildup. From an efficiency point of view, the attic is the least desirable area for locating the blower coil because of the high temperatures, easily reaching 140° F to 150° F that normally occur during the summer. Even though the blower coil is insulated, there will be a heat gain because of this high temperature. The overall attic temperature, however, can be lowered by increasing the number or size of the attic vent openings. A ridge vent is quite effective, as is a thermostatically controlled power ventilator.

Ducts After the air-conditioning system has been operational for about fifteen minutes, the air discharging from the registers should be felt to determine whether it is relatively cool. The temperature of the air discharging from the supply registers should be about 15 degrees lower than the temperature in the room. If the air does not have a slight chill, it might be because there is a heat gain along the duct leading to that register as a result of inadequate insulation, or the system may be undersized or low in refrigerant.

While checking the temperature of the air leaving the supply registers, also check the airflow. If the air discharging from the registers has a low flow and appears to be sluggish, it might indicate that there is an obstruction within the system caused by dirty filters or icing on the evaporator coils. Sometimes the condition is caused by an undersized fan or the need for balancing the airflow between the registers. In any case, the condition is abnormal and should be recorded on your worksheet.

Fig. 17-7. Auxiliary condensate drain line connected to main condensate line. This negates the use of an auxiliary drain and reflects poor-quality workmanship. If the main drain becomes clogged near the discharge end, the auxiliary drain will not function. Note that the U-shaped trap is missing.

Fig. 17-7. Auxiliary condensate drain line connected to main condensate line. This negates the use of an auxiliary drain and reflects poor-quality workmanship. If the main drain becomes clogged near the discharge end, the auxiliary drain will not function. Note that the U-shaped trap is missing.

Trap Main Drain

As with a heating system, the location of the supply registers is important for effective air-conditioning. Since cool air is heavier than warm air, the cool air will tend to accumulate near the lower portion of the room and the warm air near the top. As a result, there is usually a temperature difference between the ceiling and floor. This stratification of heat layers can be minimized by adequate circulation in the room. Adequate circulation can be achieved by locating the supply registers on the opposite side of the room from the return grille. When the return grille is near the supply register, the air discharging from the supply is drawn in by the return grille and does not have a chance to circulate adequately around the room. In many houses, the rooms do not have individual return grilles. Instead there might be a large central return located in the hall. In these cases, the supply registers should be located on a wall that will allow the supply air to circulate completely prior to being drawn off and returned to the central grille. Also, the doors to the individual rooms must be undercut so that when they are closed, the supply air will be able to flow to the return grille.

Ideally, air-conditioning supply registers should be located in or near the ceiling. To minimize air-conditioning installation costs, rather than install new ducts many new homes use the ducts and registers provided with a forced-air heating system. These registers are usually located near or at the floor level and are quite effective for heating purposes. However, when they are used for air-conditioning, they are less effective and tend to increase the stratification effect. Some houses that have forced-warm-air heating have what are called high-low registers. The duct supplying the heat register is extended vertically to a point near the ceiling level where it terminates at another register. When the system is used for heating, the damper controlling the upper register is manually closed, and the lower register is opened. When the system is used for cooling, the damper controlling the lower register is closed, and the upper register is opened. This type of arrangement is very desirable and is often found in high-quality construction.

The presence of a central air-conditioning system does not mean that the entire house is air-conditioned. Look specifically for registers as you walk through the house. In many raised ranches, I have found that the upper level is air-conditioned and the lower level is not. If you have any questions, check each room while the air-conditioning system is operating.

There are two basic types of ducts used in residential structures—sheet metal and glass fiber. While checking the distribution portion of the air-conditioning system, look for exposed ducts. The glass-fiber type of duct is by its very nature insulated. However, the metal duct may or may not be insulated. The fact that there is exposed metal on the outside does not mean that the duct is not insulated. The insulation might be located inside the duct. Whether the metal duct is insulated can be determined by feeling the duct when the system is operating (if no insulation, the duct will be quite cool) or by striking the duct with your fingernail. If there is no insulation, you will hear a ringing sound, and if there is insulation, you will hear a dull thud. All ducts that lead through unfinished areas such as crawl spaces and attics must be insulated so that the cool air flowing through the ducts will not absorb heat from its surroundings. Pay particular attention to the joints for indications of air leakage. Any open joints should be sealed with inexpensive duct tape. Also, whether the evaporator coil is located inside the furnace plenum or in the attic, check the joints around the housing for air leakage. Very often, there are open joints that must be sealed.

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