Ventilating or ventilation (the V in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air.
I need a complete system replacement , before I was trying to get an evaporator coil replaced , of course the price is between $2200 an $2800 , then get told it probably will over tax my ac unit within months , so now and like everyone else what do you buy 14 ,15 16 17 seer units ,price and how do we know its reasonable  why can't there be '" a estimated price ,in the ball park, a range of prices ,so we can at least go from their .....  Now it's from 7500 to 15000. Frustrating  from the start so everybody good LUCK.   Draw a # from the hat    Unregulated  and who do you BELIEVE, just like on NCIS go with your gut feelin   
Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce electrical power required to move the air by a third.[28]
Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's −70 °F (−57 °C) low temperature or cool a building in the highest temperature ever recorded in the US—134 °F (57 °C) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A few feet below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 6 feet (1.8 m) underground, temperatures generally only range from 45 to 75 °F (7 to 24 °C).
My mom just received service from this company. She paid $609 to have her frion replaced. After two uses the AC stops working. A young rep comes out to the house again and notifies her that her entire AC unit and furnace need to be replace for just shy of ten grand, though when her frion was refilled she was told that her system should last another five years. When they came back to tell her how her entire system needed to be replaced, they were generous enough to offer her a $300 credit on the nearly $10,000 estimate of replacing the entire system that was working fine until they touched it. My best assumption would be that there is a mishap with the system is due to their negligence. Id suggest using another company other than these scam artists.
The letters in HVAC stand for heating, ventilation and air conditioning. An HVAC system enables you to regulate your home or building’s internal temperature (thermal control) for comfortable living and working. You can bring heat levels down in the summer and up in the winter, keeping your home or office livable year-round. HVAC systems can also help with humidity levels and regulate indoor air quality in a home or office. There are many types of HVAC systems and technologies available.

If you are using existing ducting, it will have to be inspected. Proper ducting loses around 2% to 5% of your energy. Old, leaking ducts can lose 50% or more. A contractor will need to have the ducts inspected and replace any parts ahead of time. If you are changing the size of your HVAC system because of significant changes to your home, you might need to replace the ductwork regardless.

Monday the following week, no phone calls, or follow up.  I call to get an update and am told that they cannot install my system because they don't have time.  I ask what does that mean, one year? One week? Until the end of summer they say.  What does that mean I ask?  They say at the end of September.  I say thank you for wasting 1 month of my time.

Fuses -- Anyone who has worked with electrical systems knows all about fuses and how they fail. They can burn out over time, may just be loose, or can blow out during an electrical storm or due to overload from another failed component. Of course, that's what they're supposed to do; they stop surges from going through and damaging the rest of the system. When a fuse fails, whatever system it was protecting will stop working.
The belt should slip right into place. If it seems to be too tight or difficult to set in place, it may be necessary to adjust the motor mount to provide more slack. Then you can re-tighten the tension once the belt is in place. Check the manufacturer’s specifications for proper tension—in most cases, the belt should deflect about an inch when you press down on it.