How HVAC Works
March 7, 2008
Air conditioning includes both the cooling and heating of air. It also cleans the air and controls the moisture level.
An air conditioner is able to cool a building because it removes heat from the indoor air and transfers it outdoors. A chemical refrigerant in the system absorbs the unwanted heat and pumps it through a system of piping to the outside coil. The fan, located in the outside unit, blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air.
Basic Operations
Most air conditioning systems have five mechanical components:
- a compressor
- an expansion valve or metering device
- an evaporator coil and blower
- a chemical refrigerant
Most central air conditioning units operate by means of a split system. That is, they consist of a “hot” side, or the condensing unit-including the condensing coil, the compressor and the fan-which is situated outside your home, and a “cold” side that is located inside your home. The cold side consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler. The furnace blows air through an evaporator coil, which cools the air. Then this cool air is routed throughout your home by means of a series of air ducts. A window unit operates on the same principal, the only difference being that both the hot side and the cold side are located within the same housing unit.
The compressor (which is controlled by the thermostat) is the “heart” of the system. The compressor acts as the pump, causing the refrigerant to flow through the system. Its job is to draw in a low-pressure, low-temperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant. This high-pressure, high-temperature gas then flows to the condenser coil.
The condenser coil is a series of piping with a fan that draws outside air across the coil. As the refrigerant passes through the condenser coil and the cooler outside air passes across the coil, the air absorbs heat from the refrigerant which causes the refrigerant to condense from a gas to a liquid state. The high-pressure, high-temperature liquid then reaches the expansion valve.
The expansion valve is the “brain” of the system. By sensing the temperature of the evaporator, or cooling coil, it allows liquid to pass through a very small orifice, which causes the refrigerant to expand to a low-pressure, low-temperature gas. This “cold” refrigerant flows to the evaporator.
The evaporator coil is a series of piping connected to a furnace or air handler that blows indoor air across it, causing the coil to absorb heat from the air. The cooled air is then delivered to the house through ducting. The refrigerant then flows back to the compressor where the cycle starts over again.
Dear Ask Boyd,
We recently purchased a 15+ year old home from the original owner. We have an original Janitrol AC unit that is installed in the garage. We’ve recently had a series of 100+ degree days (in California). Tonight we noticed water around the base upon which the unit sits. Could this be just condensation? There is a small box on top of a larger rectangle box that has a hole that looks like it is missing a plug (we thing that is where the water is coming from). The unit is cooling the house - no changes in functioning. We haven’t noticed the water before. Oh yea, we have a home warranty. Thoughts???
First of all, thanks for visiting our site. I really appreciate that. And to reward you for your participation, I have good news for you. Your moisture problem is one of the easiest HVAC problems to cure.
The fact that you have not seen this before indicates a problem. What you are probably seeing is condensation that normally drains away from your indoor coil (that square box you refer to). You should have a drain line, either pvc, plastic or rubber leading away from your unit. That is the condensate return drain line. That line is probably clogged somewhere between where it leaves the unit and where it empties into a drain. I would bet that it is right where the drain line is connected to the unit.
If you can get to the end that drains out, you can possible blow the
obstruction back into the unit and free the flow up. The best is to remove this drain line and clear any obstruction.
I will warn though that another possibility is that the drain pan that the condensate falls into before exiting the unit could be cracked. If that is the case, replacement of the drain pan is about the only option.
Be careful not to invest too much into a 15 year old system. It is at the very end of it’s life (13.72 years is the manufactures expected longevity).
If you do decide to replace your system and are interested in saving up to 50% off, consider a partial do it yourself project where you purchase the system direct and then utilize a local contractor to hook up the system. Here is a site that will give you an idea of system costs, and they have a free report that will help help you wade through the process. http://www.homeairdirect.com
Good luck with your A/C issue.
Boyd @ Ask Boyd.com