American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.

Pro HVAC company Southern Comfort Mechanical says on its blog, “If there’s mold growth inside the handler due to excess moisture, algae in the condenser drain line or a dirty evaporator coil, it can negatively impact your AC unit’s efficiency. The filters inside may also build up excess dirt and become clogged, which will also make your AC [or heat pump] waste energy trying to sustain the cool climate inside your home.” These issues are easy to solve. They don’t require replacing the air handler.
If your central air conditioner will not cool but you can hear it running, it may just need to be cleaned. Whether or not this is the cause of the problem, it’s a good early remedy to try. Plan to do this on a relatively warm day. Never use a power washer for this—it can damage the fins. The following are guidelines; always refer to your owner’s manual. Note: Always turn off the power before cleaning the unit.
Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.
Knowing what you should be paying for your HVAC equipment and installation is essential to getting a fair deal. Most HVAC prices aren’t advertised. Contractor strategy is to get a salesperson into your home to sell you on a package of equipment, accessories and installation. This makes comparing systems difficult, and some sales pressure might be applied.
Asbestos removal tip.  Don’t trust any HVAC installation company that says that they will remove asbestos for you. They will do either one of two things: remove it and do a horrible job because they don’t know how (an illegal act in California, finable by up to $250,000), or they will say they did and never actually do it, which is dangerous to your health. Any HVAC contractor worth their weight will know not to touch it. Call an asbestos abatement company – it should cost around $500-$1,000, and your HVAC installation company will come in right after them and do the installation to decrease cost and inconvenience.
Indoor Coil -- The indoor coil is a heat transfer device. It absorbs the heat from the inside of the house and passes it on to the refrigerant and is pumped outside. Dust that builds up on the coil can hamper its ability to absorb heat. High heat transference coils use very thin metal. Airborne chemicals can cause corrosion which leads to leaks. The constant vibration of the compressor can also cause solder joints to weaken and leak. An indoor coil may operate for weeks with a tiny leak, and you may not notice the loss in performance right away. As soon as a leak is made known, it should be replaced or repaired immediately.
As you can see, if we know what the contractor is actually paying for specific equipment, we know what their labor rates are, and we know what they bid the project for, then we can also use some basic algebra (or just let the program do it for us because we’re lazy) to figure out how much of a profit they are making off of us (you) at different bid prices:
You can adjust for seasons: During the summer, you can have the air conditioner stay off during the cooler morning hours and start cooling the house as everyone gets up and starts moving around. During the winter, you can have your heater stay off while you are away at work and turn on about a half hour or so before you get home so that you are coming home to a nice, warm house.

Air conditioner size is measured in “tons.” However, the tonnage of an HVAC unit is not actually based on its weight. A “ton” is simply a measure of an air conditioner’s ability to cool your home. One ton is the ability of your air conditioning system to cool 12,000 BTUs (BTU stands for British Thermal Unit) in an hour. Likewise, a “2-ton” central air conditioner is able to cool 24,000 BTUs per hour.

At the state level the rebates are still substantial. For example, switching to a zoned system can get you a $100 rebate from various A/C companies, and state rebates are also included. In Pennsylvania a high-efficiency air conditioner alone can get you up to $300, and a high-efficiency complete HVAC system can see up to $1000. Maryland's incentives get up to $1,250, with a $100 rebate on a tune up of an existing system.
But Tim, doesn’t this mean that a less-than-honest air conditioning company can just charge what he wants and say that it’s a difficult job? No. You see, dishonest contractors, typically, aren’t the brightest people (I figure if you’re still reading this, you’re warming up to me so I’m taking off the training-wheels). They aren’t smart enough to take difficulty into account, and will probably get confused if you ask them about it. They will tell you things like, “that’s how much the unit costs,” or “California has a new law that magically adds $5,000 to the price.”  Trust me, follow your gut, and you’ll be able to tell who the honest contractors are...or just use one of our ASM-approved contractors.
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   

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7 To test it, turn the thermostat to OFF, reset the power at the disconnect next to the compressor and the main panel. Set the thermostat to a temperature below the room temperature, and then switch it ON. To avoid straining an air conditioner’s compressor, wait at least five minutes between turning it off at the thermostat and turning it back on. You should hear the outdoor compressor run and see the fan turning inside the top. If the fan isn’t turning, look for an overload button or switch to reset (not all types have this).