Air conditioning is often seen as a luxury item, but studies show that installing a proper central A/C system in a new home during construction adds to long term comfort and much of the cost can be reclaimed at resale.

 How do they work?

Air cooled air conditioning systems usually work in conjunction with a forced air furnace. These systems have two main components:

  1. the evaporator unit (above heat exchanger)
  2. the condenser (located outdoors)

The refrigerant (Freon) enters the evaporator as a cold liquid and absorbs heat from the household air to boil the liquid and turn it into a gas. This gas moves outdoors to the condenser unit. The compressor squeezes the gas into a smaller volume in the condenser coil.

A fan in the condenser unit blows outdoor air across the coil and cools the gas. As it cools, it condenses into a liquid. The liquid then passes through a pressure reducing device which causes the temperature of the liquid to drop below that of the household air. This liquid travels back to the evaporator coil where it is evaporated into a gas again, and the cycle continues.

The Compressor

The compressor is the heart of every air conditioning system. It is responsible for moving the refrigerant through the system. The life expectancy of a compressor is typically ten to fifteen years in moderate climates, and eight to ten years in hot climates. Unfortunately, from a visual inspection it is not possible to tell whether the compressor in the system is the original or a replacement. Also, residential compressors are hermetically sealed, and cannot be closely examined. The compressor constitutes about fifty percent of the cost of the entire system and depending on the age, replacement of a failed compressor may not be cost effective. It may be better to replace the entire condensing unit rather than just the compressor.

Indoor/Outdoor Coils

The coils are constructed of copper or aluminum and have very fine fins attached to improve heat transfer. They are subject to corrosion, blockage and leakage. Air flow across the coil can be inhibited by dirt or other foreign matter. Damaged fins will reduce efficiency.

Condensate Tray

When an A/C system is cooling, household air passing across the evaporator coil causing condensation to form and is collected in a condensate tray. Occasionally, water stains are visible on the top of the furnace indicating a cracked or broken condensate tray.

It is essential that the condensate tray function properly or the excess water will drip onto the heat exchanger (the most critical component of the furnace). Water dripping on a heat exchanger can rust it prematurely, requiring furnace replacement.


Install new A/C System on new furnace

High Efficiency Unit……………….$2000-$3000

Conventional Unit…………………$1500-$2500

Install new A/C System on existing furnace

High Efficiency Unit……………….$2500-$3500

Conventional Unit…………………$2000-$3000

Annual Service Charge……….$75 – $125

High Efficiency Air Conditioners

The main difference between a high efficiency A/C and a conventional A/C is the compressor. On a high efficiency A/C the compressor is made more efficient, thus reducing the hydro required to operate the system.

Sizing Your System

Most air conditioning systems are rated in TONS (ie.2, 2.5,3.0 tons). A ton represents 12,000 B.T.U’s per hour. Cooling systems are sized by calculating the heat gain for the house which is dependent on the construction, the amount of insulation, the type, size and orientation of windows. As a general rule for moderate climates, most houses should have 1 ton for every 700 sq. ft. of living area. Note however, when equipment is oversized (a common problem) efficiency is reduced, operating costs are increased and control over space conditions is lessened. Optimum cooling efficiency occurs when equipment operates at full load for long periods of time.

Running a larger air conditioner for nine minute cycles instead of five minutes will increase energy efficiency by about 10 percent.