Air Conditioning - But how does it work?

Can anyone refer me to a site or a book for a basic education on how central air conditioning works? We bought a 50-year-old ranch with a fairly new central air system which works great. We converted the existing attic to a large open living space and, before the drywall was hung or the floors installed, had duct work put in for central air later on (ran out of $ doing the renovation).

The time has come to bring the central a/c upstairs, and everyone I talk to has a different idea of how to do this. They all sling a lot of lingo but none of it makes sense to me. This is what I hear: "You could route the frammis over the ballast-keeper but the wingbats will interfere with the snarkle unit." But then the next guy says "Forget the snarkle unit. No one uses wingbats any more. What you need is a convotreader and persalor refractor."

I need to educate myself before any more of these folks tries to snow me with verbiage. Help??

Just put in a unit for the upstairs and let the down stairs have its own unit. You will be happy and cool. Get 3 bids and make sure they run a heat loss and AC load on the upstairs.

ED;)

I agree with Ed.

They make nice units that hang on the wall (sanyo mitsh,) They work great and quiet.

Just put in a unit for the upstairs and let the down stairs have its own unit. You will be happy and cool. Get 3 bids and make sure they run a heat loss and AC load on the upstairs. ED;)
Yes, that is exactly what I want to do ... after I understand the meaning of "heat loss and AC load", the difference between "air handler" and "condensor", and in general how the system works.
:wall: Getting 3 quotes won't do me any good if I don't understand what they are quoting me on.
Any ideas of good books or sites where I can learn about this stuff so I don't have to take it on faith that they are doing it right??

There are probably hundreds of sites with that information. Wikipedia is a favorite of most but here on the forum we generally do not refer people other web sites. In fact, this may get edited out. We should have an in-depth FAQ with all of this info in it..maybe the moderator can use this thread to start compiling one *hint*

An A/C system is composed of many individual parts. Over the years companies have packaged systems in a variety of ways but the theory remains the same.

A compressor compresses freon gas into a liquid state where it passes through a condensor coil to remove as much heat as possible then into a small tube to a device which restricts the flow. This device could be one of several different devices, capilary tubes, thermo expansion valve, etc.. This device 'meters' the flow of freon into a larger tube wherein the freon turns to gas and gets real cold. (Physics...compressed gas passing from small tube to large tube simply gets cold due to sudden pressure change.) At this point the large tube is broken up into many tubes and goes into a coil. Air is passed over the coil to cool the air. During this process humidity is also removed from the air. This causes condensate (water) that needs to be drained off and disposed. The freon gas, now travels back to the compressor to be compressed again.

The compressor in modern residential units are packaged with the condensor coils and commonly called a condensor unit. A 'condensor' fan is used to force air through the coils. (Commercial units may have the condensor coils and compressor as separate units, or even water cool the freon.) The condensor unit sits outside of the house. The condensor unit also contains the necessary electrical switching device called a contactor, and various capacitors that store up electrical energy that helps the fan and compressor start and run.

A set of tubes, or line set, connects the condensor unit with the components inside the house. Small tube high pressure liquid going into the house, large tube low pressure gas coming from the inside to the compressor.

Inside the house, the various components are either packaged into a single unit or are modularized. A packaged unit is commonly called an 'air handler' and consists of a blower (that either forces air across the evaporator coils, or sucks the air across the coils,) the restriction device whatever is used, the evaporator coils, heating component if the unit also provides heat, and of course, the evaporator coils. Also, it may contain the related electrical components to control the unit.

Now that a fan is forcing air over the evaporator coil you have cold air that you want to divert that air into your living area. From the air handler the air goes into a 'plenum.' It is just a box that all the air goes into, and all your ducts connect to so that it can be distributed to individual rooms.

Once the air is in your living area you want to circulate that air back into your air handler so that you are recirculating the air and not bring new air into the house. So, the air circulates back to your air handler through a return air. This is where your filter is usually found.

To round up everything, a thermostat is placed in a convenient place away from conditioned air and generally close to the return air so that it can allow the user to control the functions of the system.


Now, the pros can critique, correct, and add. Much to add... probably some to correct, and likely a lot of terminology will be thrown in...

And now that you understand all the principals...

There are 4 basic types of A/C systems used in residential. In order of complexity and, usually, price:
Evaporator and condenser are housed in a single box. The box is mounted in a window or wall and cools the room it's in. Called a "window" or "wall" unit (sometimes lovingly referred to as a "window shaker").
Evaporator and condenser are separate. The evaporator is mounted in a box in the room to be cooled and the condenser is mounted in a box outside. Called a "mini-split" or "ductless" unit. Evaporator and condenser are mounted in a single box. The box is located outside and ducts are run into the room or rooms to be cooled. Called a "package" or "self contained" unit. Evaporator and condenser are separate. The evaporator is located in a central location with ductwork providing cooled air to multiple locations and the condenser is mounted in a box outside.

If you already have the ductwork installed, you've chosen the forth type. You'll need an evaporator (generally referred to as an "air handler") mounted where it can connect to the ductwork and a condenser placed somewhere outside. The condenser and evaporator will connect to each other via 2 copper tubes and a small cable with multiple low voltage wires. The air handler will need 120V power (unless it also has electric heating capabilities in which case it'll need 220V power connections) and a drain line to drain the condensate water that it removes from the air. The condenser unit will need a 220V power connection.

Choosing the correctly sized equipment and location for it that is convenient for all the needed connections should be your only consideration. Use the heat-loss calculation (often called a Manual J - performed by the company providing the quote) to determine correct sizing of the unit and choose the most efficient unit you can afford (determined by the SEER rating - the higher the SEER, the more efficient). One feature that is very desirable is a variable (not to be confused with multiple) speed blower (located in the air-handler) which will be quieter and slightly cheaper to run. Choose a unit with this feature if you can afford it.

This completes your crash course in residential A/C. If anyone proposes that you route the frammis over the ballast-keeper, tells you that the wingbats will interfere with the snarkle unit, or advises you to forget the snarkle unit because no one uses wingbats any more, you'll know to politely ask them to leave because they aren't talking about A/C. Besides, everyone knows that wingbats are still included with the every MS OEM OS and function harmoniously with the snarkle unit. What most people unfortunately don't realize is that the ballast keeper must always be held firmly in place above the frammis with a widget to avoid injury.

If you would like, we can offer a similar course on heating in one of the multiple heating forums. :)

Doug M.

AND all you need to make it a heat pump is turn the whole thing around. Like when you have a window unit you get cool air inside and it blows hot air outside. Take it out of the window and turn it around. Now you have cool air outside and hot air inside and thats how we make it a heatpump. We just do it with valves is all.

ED:D just .02 cents more

Take it out of the window and turn it around. Now you have cool air outside and hot air inside and thats how we make it a heatpump. Ed, I tried that once, but I always had to go outside to turn it off and on. :D (duck and run)

Doug M.