Central air conditioning
A true central air conditioning system uses ducts to distribute cooled air throughout the house. In a 'split system,' the most common design, refrigerant circulates between an indoor coil and a matching'meaning from the same brand'outdoor condenser with compressor (see the illustration below). The refrigerant cools the air, dehumidifying it in the process; a blower circulates air through ducts throughout the house. A thermostat maintains the temperature at the setting you select.
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Split ductless systems
Split ductless systems have an outside condenser and compressor, and one to four or more indoor blower units, called air handlers, mounted high on the wall, that distribute air. The indoor and outdoor sections are connected by a thin conduit that houses the power cable, refrigerant tubing, and a condensate drain. The conduit is run through about a 3-inch hole hidden behind each air handler. Each air handler cools the room in which it's installed, and you set the temperature with a remote control. Professional installation is recommended. While not technically central air, they're much quieter and more efficient than window ACs or portable ACs and can be an easier, more affordable option to install than a true central air system.
You can also consider an air-source heat pump in place of an AC-only system. Heat pumps can provide both heating and cooling. In cooling mode, they work exactly like air conditioners. And come colder weather, they're the most energy-efficient system for home heating.
They've been common in warm parts of the U.S. for decades, but now there are plenty of air-source heat pumps that can provide most or all of a home's heating needs, even in cold climates. You can also use a heat pump in combination with an existing or supplementary heating system. An installer can set it up so that the heat pump operates most of the time, but then when the outdoor temperature drops below a certain threshold and the heat pump becomes less practical, another system'such as a gas-fired furnace'will kick in. (A guideline for that threshold is about 20° F, but the cutoff can be a little warmer or much colder depending on the system.)
Heat pumps are available in ducted or ductless versions. (Some so-called ductless air conditioners are actually heat pumps.) They tend to cost a little more than AC-only units but less than the combined cost of a new heating and cooling system. Because heat pumps are so energy-efficient, some state governments offer tax incentives or even direct cash rebates to homeowners who install air-source heat pumps, which sometimes make them the lowest-cost option for home heating and cooling. Read our heat pump buying guide for more.
If you are installing an AC system from scratch, your contractor should calculate the size of the cooling equipment you need using recognized methods, such as those you'll find in the Residential Load Calculation Manual, aka Manual J, from the Air Conditioning Contractors of America (ACCA).
If your home already has ductwork but you're installing your first AC system, keep in mind that ducts used for heating might not be the right size or in the right location for optimal cooling. Your contractor should ensure that duct sections are properly sized and that there are enough supply registers to deliver sufficient air to the right spots. Undersized ductwork can lead to inefficient and noisy operation.
Also, it's wise to make sure your ducts are sealed and insulated. Otherwise, air can escape, wasting 20 to 30 percent of the energy used to run your system. Sealing your ducts will keep you cooler in the summer and warmer in the winter.
Size, aka Capacity
An air conditioner's size'which is an indicator of its cooling capacity'is measured in British thermal units per hour (Btu/hr.) or in 'tons.' One ton of cooling equals 12,000 Btu/hr. For rough sizing guidance, check the Energy Star website. But the best option is to have your contractor do a load calculation based on a recognized method, such as one in Manual J from the ACCA.
It's important to pick the right AC capacity for the size of your home. A unit that's too small will struggle to keep your home comfortable. An oversized unit will cost you more to purchase, and (unless it's a model with a variable-speed compressor) will cycle on and off more often than it should, stressing the components and struggling to control the humidity in your home.
If you're replacing your central air, you should look into whether you really need the same size system as your old unit or if you can shrink it a bit. Any changes you've made to improve your home's energy efficiency, such as upgrading your windows or adding insulation, can reduce your cooling needs. On the other hand, if you've added rooms, you might need more cooling.
Efficiency
This describes how much cooling the unit delivers for each watt of electricity. Efficiency is expressed as the seasonal energy-efficiency rating or SEER. The higher the SEER, the greater the efficiency. Higher-SEER ACs tend to cost more, but they'll often pay for themselves over time through lower energy costs. The minimum SEER allowed for a new split system central air conditioner in the U.S. today is 14, which is at least 20 percent more efficient than minimum-efficiency models made even 10 years ago. Systems that meet the Energy Star guidelines for efficiency have a minimum SEER of 15. The most efficient models reach a SEER of at least 26.
Noise
According to our reader survey, quiet operation is the feature that's the best predictor for an owner's overall satisfaction with their air conditioner. Manufacturers publish the noise levels for their products across a variety of outdoor temperatures and fan speeds, measured in decibels. A lower rating is better, especially if the AC will be installed near a bedroom window.
Reliability
Reliability is the second-best predictor for an owner's overall satisfaction with an air conditioner (tied with how quickly it cools a room, though that has more to do with whether the AC is sized correctly for your home and whether it's maintained properly). Consumer Reports rates the predicted reliability of 22 central air conditioner brands, based on data that members have shared about more than 13,000 new AC units they bought and installed in their own homes between and .
Central AC systems need regular maintenance for optimal performance. When arranging your installation, it's worth negotiating a service plan that combines regular inspections with discounts on repairs and a labor warranty into the overall price. Prices for such a service can vary widely.
Here's what you'll want the service technician to handle: Once a year, have them clean and flush the coils, drain the pan and drainage system, and vacuum the blower compartments. The contractor should also check to make sure that the system is properly charged with refrigerant, that there are no leaks, and that all mechanical components are working properly.
You can also handle some of the maintenance on your own. Clean grilles and filters monthly. Clear debris and dirt from condenser coils and check for blockages in the drainpipe. Follow the AC manufacturer's recommendations for changing the filter as well as the filter manufacturer's recommendations for how often you should change the filter. In general, the thicker the disposable filter, the less often it needs to be changed. (The HVAC filters we test last between three and 12 months.)
If your HVAC system was installed before , it may rely on the refrigerant Freon, a trademark name for several different refrigerants including chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons such as HCFC-22 (or R-22). These chemicals deplete protective ozone from the atmosphere. The Environmental Protection Agency phased out CFCs in the s and HCFCs in .
The Environmental Protection Agency has since allowed the use of R-410A, another ozone-threatening HCFC refrigerant, but started requiring manufacturers to stop producing units with R-410A in . While manufacturers are still allowed to sell and install any units they created prior to , the industry has largely started migrating to R-454B and R-32. Manufacturers are still allowed to produce individual parts to service systems that use R-410A, but it may be worth shopping around for a central air system that uses the new refrigerants to ensure access to long-term support, maintenance, and safety.
If you still have a system that uses HCFC, you aren't required to replace it now. It's only an environmental threat when it leaks, so ask your technician to check for leaks during your annual maintenance visit. Better yet, consider replacing your AC system with a newer one. It will not only be better for the environment but also be more energy-efficient.
Programmable thermostats. Setting your smart or programmable thermostat at the right temperature can reduce your cooling costs by about 10 percent. The right temperature depends on your comfort level, but start by setting it at 78° F and experiment until you find the sweet spot. You'll save about 3 percent on your utility bill for every degree you raise the set temperature for your central air, according to the Department of Energy. And keep in mind that using a box or ceiling fan, which costs little to run, can make you feel 3° F to 4° F cooler.
Outdoor space. The compressor needs adequate airflow to operate correctly, so make sure to keep at least 2 to 3 feet of space between the unit and any plants or structures. There should also be 5 feet of clearance between the top of the unit and any trees above. You'll also want to make sure there's enough space for you or a technician to access and service the unit. And your local building codes might have regulations about how close an outdoor compressor is allowed to be to a neighbor's window or property line.
Whether you're replacing an older air conditioner or installing one for the first time, finding a trustworthy contractor to install and service the air conditioning system matters the most. Here's what to do.
Ask around. Seek referrals from neighbors, family, or business associates. It's wise to get price quotes from at least three contractors.
Check their background. Contractors who bid on your installation should show you verification of bonding and insurance, plus any required contractor's licenses. Check with your local Better Business Bureau and consumer affairs office for complaint records. It's a plus if technicians are certified by a trade organization, such as North American Technician Excellence or HVAC Excellence, to service residential heating and cooling equipment. Those and similar programs assess the technician's knowledge of specific types of equipment and their proper service methods.
Get specifics. Contractors who bid on your job should calculate the required cooling capacity using a recognized method, such as one found in the ACCA's Residential Load Calculation Manual, also called Manual J. An additional reference for assessing ductwork needs is Manual D. The calculations produce a detailed, room-by-room analysis of cooling needs. Ask for a printout of all calculations and assumptions, including ductwork design. Be wary of a contractor who bases estimates merely on house size or vague rules.
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You're thankful your car A/C helps keep the cabin cool on sweltering summer days. But do you understand how the A/C system works and how to keep it maintained? This guide covers the nitty gritty details of your vehicle's A/C to help you catch problems early on and keep it in excellent shape.
Believe it or not, there's no ice machine hidden inside your car A/C. That blast of chilly air is actually hot air with the heat removed during a multi-step process.
When you turn the A/C on, the compressor compresses the system's refrigerant, raising its pressure and temperature. The refrigerant loses heat as it flows through the condenser. Typically, it then passes through the receiver/dryer, where contaminants and moisture are removed.
Then, it's on to the expansion valve. Here, the refrigerant loses pressure and temperature as it enters the evaporator, chilling it.
The evaporator is like a mini radiator in the dashboard. Air gets blown through the chilled evaporator, which cools and removes moisture from the air. The ventilation system blows that cool, dry air into the passenger compartment. Your air conditioning system works hard so you can get that refreshing, cold air.
There's no set schedule for inspecting your A/C ' it's all about how the system feels. Are you refreshed and cooled with full airflow when your vehicle's A/C is pumping? If you answered, 'Yes, I am as cool as a cucumber,' you can cross A/C inspection off your list.
Do you fall into the 'my A/C is not cold enough' or the 'my A/C doesn't work in the heat' side of the spectrum? Don't sweat; stop in for an A/C Performance Check, and we'll have you back on those hot summer streets cooler than ever.
Modern air conditioning systems don't need to be recharged on a set schedule. Most drivers can go years before needing one. However, you'll likely notice when it's time for a recharge. Signs your A/C might need to be recharged include hot or warm air coming from the vents, refrigerant leak, weird smells coming from the vents, and an A/C clutch that won't engage. (We'll cover all of these potential symptoms below!)
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To help keep your cabin cool, your A/C relies on several components. Let's take a closer look at these A/C system parts and their roles in giving you that refreshing blast of cool air.
The compressor is the core, primary part of every A/C system. They control temperature output with an electrically operated clutch. This clutch turns on and off whenever you change the temperature or if the HVAC module senses it has reached the desired temperature. If the ambient air temperature drops below the programmed value, the compressor clutch may not engage.
Before the compressor turns on, a special electromagnetic clutch (the compressor clutch) engages and disengages the compressor cycle. The compressor clutch engages the compressor, turning it on or off when commanded.
Consider the A/C condenser the master of turning hot refrigerant gasses into liquid. The condenser is mounted at the front of most vehicles, usually in front of the radiator. Outside ambient air passes through the condenser, condensing and cooling the hot refrigerant gas into a cool liquid refrigerant.
The receiver/drier is found on vehicles with a thermal expansion valve. It's the safety net responsible for helping trap and prevent harmful debris and moisture from reaching the compressor and other vital A/C parts. The receiver/drier should be replaced anytime the A/C system is opened for repair or if a technician determines moisture or debris has damaged your receiver/dryer performance.
An accumulator is similar to a receiver/drier but is only on vehicles with an orifice tube. If you have an accumulator, you do not have a thermal expansion valve.
The accumulator:
You will need to replace the accumulator if the A/C system is opened for repair or if a technician determines moisture or debris has damaged your accumulator's performance.
The orifice tube or thermal expansion valve is located between the condenser and the evaporator. It constantly monitors the pressure and temperature of your A/C system to determine the exact amount of refrigerant that can safely enter your evaporator. If too much or too little refrigerant enters the evaporator, you could have a big problem.
An orifice tube may also contain a fine mesh screen to block contaminants from the rest of the system.
The evaporator is located behind your dash and is responsible for cooling cabin air and removing moisture. Low-pressure refrigerant traveling through the evaporator cools it. This allows the evaporator to absorb heat from the cabin air, dropping the temperature of the air blowing out of the vents. If cold, refreshing air hits your face, the evaporator is working like a champ.
The clutch cycling switch cycles the compressor according to the pressure in the accumulator. This action helps to prevent the evaporator from freezing. Although most cars can blow air at temperatures as low as 60 degrees, the temperatures inside the evaporator core can get cold enough to freeze the entire core completely.
The clutch cycle's job is to ensure the evaporator doesn't reach the point of glacier temperatures.
Refrigerant (often referred to by the DuPont trade name Freon) is a specially formulated cooling agent that can transform from a liquid to a gas and back again. It absorbs and releases heat, ultimately leaving cool air behind.
Different devices, such as your home refrigerator, home A/C system, or vehicle, may use different refrigerants. They may or may not be the same.
The three common car refrigerants are R-12, R-134a, and R-yf. Different refrigerant types require different charging hoses, so check which one your vehicle is it in earlier models.
The refrigerant service port is the connection point where new refrigerant can enter the system during an A/C system recharge or where you can remove refrigerant from the A/C system. There is a service port located on the low side and high side A/C lines. Only properly equipped, certified, and qualified persons should perform A/C recharging services. The EPA (Environmental Protection Agency) requires anyone who services automobile air conditioning systems to be EPA Section 609 Certified.
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