Central Air Conditioning Systems

The most common central cooling system is a split system, which includes an outdoor cabinet containing a condenser coil and compressor, and an indoor evaporator coil, usually installed in conjunction with your furnace or air handler. The compressor pumps a chemical called refrigerant through the system.

An air conditioner seems as if it cools your home's air, but it actually makes your home air less warm by removing heat from the indoor air and transferring that heat to the outdoor air.

Heat is extracted from the home by passing indoor air across a refrigerant coil in the indoor unit. Refrigerant lines then carry the heat to the outdoor unit, where it is released into the outside air. The cooling cycle continues until the indoor temperature reaches the thermostat setting.

More specifically, when warm air inside your home blows across the indoor evaporator coil, its heat energy transfers to the refrigerant inside the coil. That transfer, in turn, “cools” the air. The refrigerant is pumped back to the compressor where the cycle begins again. The heat absorbed by the refrigerant is moved outside your home while cooled air is blown inside. Moisture that contributes to humidity is also condensed out of the air.

Your central cooling system is usually combined with your central heating system because they share the same ductwork for distributing conditioned air throughout your home.

The only reliable way to determine the size that best matches the needs of your home is to have a qualified air conditioning contractor perform a load calculation, which takes into account the square footage of your house, the insulation value of your windows, the amount of insulation in your walls and roof and many other factors.

SEER (Seasonal Energy Efficiency Ratio) is a system for rating the efficiency of cooling equipment. The higher the SEER rating, the less your unit will cost to operate. SEER ratings range from 13 SEER (which is the lowest possible efficiency air conditioner product that is manufactured - and thus is the unit which uses the most energy to operate) to over 20 SEER (the most efficient manufactured air conditioners which uses the least amount of energy).

Two-stage cooling means the air conditioner (or heat pump product) has a compressor with two levels of operation: high for hot summer days and low for milder days. Since the low setting is adequate to meet household cooling demands 80% of the time, a two-stage unit runs for longer periods and produces more even temperatures.

Longer cooling cycles also translate to quieter, more efficient operation and enhanced humidity control. Compared to a single stage unit, a two stage air conditioner (or heat pump) can remove twice as much moisture from the air. This is important because when moisture levels are high, there's a higher potential for mold and other pollutant problems.

"Variable speed" refers to the fan motor inside your air handler—the indoor part of an air conditioner that moves cooled or heated air throughout the ductwork of your home. An air handler is usually a furnace or an air handler unit (also called a blower coil).

Unlike conventional single speed motors, a variable speed motor runs at a wide range of speeds to precisely control the distribution of heated and cooled air throughout the home. Better airflow control has several benefits:

Electrical Efficiency
Variable speed motors can actually save you money on your energy bills, as they consume less electricity than standard motors.

Cooling Efficiency
Variable speed technology also means you will gain air conditioning efficiency or SEER.

Zoning
Variable speed motors are excellent for zoning, which allows you to customize your comfort in different areas of your home and control your energy bills.

Air Quality
A variable speed motor can also help clean the air in your home. When the fan is in constant operation (indicated by the "fan" setting on your thermostat), the motor will continue to slowly circulate air, allowing filters to capture more contaminants.

Humidity Control
A variable speed motor combined with a humidity control thermostat allows you to control the amount of humidity in your home for improved indoor air quality and comfort.

The answer is most likely YES, but this is mainly due to the following key reasons:

Matched System Design
All outdoor cooling units are specifically designed to work with matched indoor units for optimum efficiency and performance. Air conditioners may "work" with other indoor units, but the result is a definite compromise in overall system performance and efficiency.

Design Advances
In recent years, indoor blower coil units have undergone numerous design advances, especially in the areas of air handling performance, filtering efficiency and operating sound levels. A new outdoor unit will also include the latest design advances.

Higher Cooling and Heating Efficiency
The cooling and/or heating efficiency rating assigned to a given air conditioner is based on matched system performance. While you may gain higher efficiency by replacing only the outdoor unit, the efficiency levels (and savings) will be compromised unless a matched system is installed.

Equipment Age
If an air conditioner outdoor unit is 10 years old and needs to be replaced, the indoor unit is just as old and has been subjected to the same amount of wear and tear. Replacing both units means you won't have to replace the indoor unit a short time later and you’ll enjoy years of service from both units.

New Warranty
A new unit also gives you a new product warranty. Replacing the indoor unit at the same time as the outdoor unit gives you added peace of mind, knowing the new warranty covers the entire system.

Cost Savings
At first, replacing only an air conditioner unit may appear to be a bargain. That is, until you consider the lower efficiency, decreased reliability and high cost of ownership associated with single unit replacement. It may cost more to replace an entire system, but this gives you more efficiency, reliability and comfort.

Choosing the right thermostat to control operation of your cooling system depends a lot on the equipment you have. Your qualified heating and cooling contractor should offer a complete line of thermostats, both programmable and non-programmable models, each designed to maximize the performance of your cooling system.

The most important maintenance you can do is to change your filters regularly. Ground mounted outdoor units need to be kept clear of debris, clutter, weeds or landscaping that can grow too close and reduce the airflow to the unit. Also, keep pets away from the unit because pet urine can cause expensive damage. Use caution with a weed trimmer around the unit to prevent damage to the control wiring or to condenser coil fins. Any additional maintenance should only be performed by a qualified contractor.

There are several factors that can cause system freezing.

Dirty Filter
The main thing you can do to prevent or correct this problem is to make sure the filter is clean or replaced. You can check to see if airflow is restricted. Restricted air flow not only reduces cooling output, but it also damages the compressor and reduces equipment life.

After replacing or cleaning the filter, you can speed up the thawing process by turning the system off and turning on the fan. If you have a heat pump system, you can try turning the system to heating mode until the ice has melted. After the ice has melted, switch the system settings back to normal. If the system refreezes, contact your heating and cooling contractor to correct the problem.

Low Refrigerant
In some cases, freezing is caused by a leak in the refrigerant lines. Weak solder joints, corrosion, friction from piping rubbing or vibrating against an object, open valves or loose fittings are all factors that can cause leaks. When determining whether to have the system repaired or replaced, the age of the system and the nature and location of the leak are important considerations. Your qualified contractor should utilize the latest technology refrigerant leak detectors to identifiy leak spots. Some leak spots may be so small that they are undetectable while other identified leak spots can be repaired. Often when there is one leak, there are multiple leaks and the best course of action is to replace the entire leaking coil.

Dirty Evaporator Coil
Over time, the evaporator coil will become dirty. When this happens, you will begin to lose airflow slowly enough that you probably would not realize it until it freezes up or cooling performance is compromised. At this point, you will need your qualified heating and cooling contractor to clean your indoor coil to correct the problem.

Defective Blower Motor or Relay
A blower motor not running at the proper speed or not running at all is another factor that can cause freezing. Motor operation may be intermittent, starting at full speed and slowing down after it heats up. A faulty relay could cause the unit to start one time and not the next. In either case, you will need to contact your qualified contractor to correct the problem.

There is no exact answer for how long your system should run during each cycle. The average air conditioner is sized to remove the heat from your home as fast as it comes in, on a 100° day. Therefore, ideally, on a 100° day the system should be able to keep up with the incoming heat, but not gain on it and be able to turn off. The cooler it is below 100°, the more the system will cycle on and off.

Every time your system starts up, it will use a lot of electricity and not produce much cooling. Usually a system that is too small to cool the home is more economical to run but delivers less comfort. Even though it runs non-stop, it will usually consume less power than a larger system that cycles on and off. As a rule of thumb, a unit that cools (although with a longer run cycle) is typically less expensive to operate than a unit that is cycling on and off.

The air temperature your system produces depends on the temperature of the air going into the system. Generally, the air produced should be 18°-20° below what enters the system. So if the air entering the system is 80°, the air exiting should be about 60°-62°. However, that only works on a system that has been running at least 15 minutes on a warm, dry day with a home that is about 80° inside. On a mild day, with an indoor temperature in the low 70's, or during humid conditions, the air coming out may only be 15°-17° cooler than the temperature of the entering air.

Yes. Several manufacturers have developed new systems that contain the environmentally friendly R410-A, or Puron, refrigerant.