HVAC | Air Conditioning | Gas Furnace System | Boiler hot water Heating | Air Conditioning Heat Wave
Contents: Overview | Troubleshooting: | AC Icing: | Maintenance: | PSE&G's Cool Customer Program (Radio-shutoff): | Terms: | Links:

air conditioning system diagram, condenser, compressor evaporator, motor, fan

Note: In a combined heating - Air Conditioning system (HVAC) the blower fan and heating system is usually below the AC evaporation coils. (diagram)

The system works on the principal that when pressure is released from a liquid allowing it to expand to a gas it absorbs heat in the process (enthalpy of vaporization) i.e. becomes cold.
In thermodynamics it is referred to ast the P-h (Pressure Enthalpy) principal. This is the end of the techie part. The rest of this tutorial does not require a PhD in physics.
As warm house air passes over the cold coils heat is transferred to the refrigerant. It then takes this gas outside where pressure converts it back to a liquid and squeezes the heat out (not a scientific term) in the process. The heat is released into the outside air.
Basic Refrigeration Cycle
Pressure Enthalpy Diagram for the Mechanical PE Exam
See Terms below.

The compressor/condenser outside your house requires a lot more power (abt. 4,000 watts for a 2 ton system) than the blower motor inside (abt 460 watts) and the condenser usually has a 240 volt motor vs 120 volts for the blower, so they will require separate electrical circuits and circuit breakers.
Note: Power requirements vary depending on the efficiency of the system.

If your air conditioner is not working here are some things to check.

Air conditioner is not cooling the house down.

  • Hold your hand in front of an air duct. It should be cool.
  • If no air is coming out there may be a problem with your thermostat, control board or fan on the inside unit.
  • If air is coming out but it is not cool, go outside and see if the fan on the condenser unit is running.
    The condenser is on a different circuit than the blower fan which circulates the air in the house, so it may be off even though air is still coming thru the duct.
  • If the condenser fan is off, check the fuse box to see if the circuit breaker has flipped.
  • If it has, reset the circuit breaker.
    This may be a sign of another problem, so you should probably lower your temperature setting so the unit is not running constantly and call a service technician.
  • If the air coming out is not as cool as normal you may have a problem.
    Put a thermometer in front of an air duct (closest to the AC unit) and a return duct (place a tissue over the duct to see which way the air is blowing). The temperature difference should be 14-20 degrees.
    There may also be a little hole in the duct by the evaporator inside your house. If you cat fit a thermometer in this hole the temperature should be about 25° cooler than the room temperature. If See "Test Your Central Air's Cooling Ability" | Lowes.com
Air Conditioner Troubleshooting, A Homeowner's Guide To Air Conditioner Repair
Central Air Conditioner Troubleshooting & Repairs | HomeTips

AC Icing:
A common problem with air conditioners is icing or freeze up.
You will see ice on the outside condenser/compressor and the inside coils (the inside coils are behind the duct work so more difficult to spot).
Turn it off and let the ice melt. The outside ice will melt quicker, while the inside ice may take overnight.
Give it 4-5 hours to melt before a service technician shows up. They can't do anything while it is still frozen.

It can be caused by several things:

  • Low freon level:
    "If your air conditioner is low on Freon, then your air conditioner can freeze up due to lower pressure inside the system. This is because now there is less refigerant in your system, but it is still being forced to expand the same amount - more expansion equals a cooler temperature. As your air conditioner's evaporator coil drops below freezing, the moisture in your air will freeze as it comes into contact with your coil causing it to ice up."
  • Clogged filter:
    Your air conditioner is designed to drop the temperature of your house by taking heat from it as iside air blows across the evaporator coils. If there is insufficient flow the evaporator coils will get too cold and freeze up.
  • If you are running your air conditioner when the outside air is below around 62 degrees, then the pressures inside of your system will drop and this can cause a freeze up
Coils Frost Up When Running the Central Air | Home Guides | SF Gate

An improperly maintained system can loose 5% efficiency, which could cost $50 - $100.

  • Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house. See label on filter box for guidelines.
  • Put bleach or tablets in the condensate system. Some have a removable cap on the pipe. The tablets need to go into the condensation tray, which is not accessable on many systems. My 25 year old system has no access to either the drain pipe or tray.
    Pass a stiff wire through the unit's drain channels.
  • If you can get at it check your evaporator coil every year and clean it as necessary.
    You usually cannot get access to the evaporator coil. It may be possible by removing some foil duct and removing some screws and bolts.
  • Check your outdoor condenser coils every year and clean as necessary.
    Remove foliage blocking air flow to the coils.
Professional Maintenance Service:
It is probably a good idea to fork over the $70 - $100 for an annual maintenance (at least every few years) which should include, Inspection checks coils, capacitors, compressor & refrigerant.

A more complete checkup would include:

  • Check for correct amount of refrigerant
  • Test for refrigerant leaks using a leak detector
  • Capture any refrigerant that must be evacuated from the system, instead of illegally releasing it to the atmosphere
  • Check for and seal duct leakage in central systems
  • Measure airflow through the evaporator coil
  • Verify the correct electric control sequence and make sure that the heating system and cooling system cannot operate simultaneously
  • Inspect electric terminals, clean and tighten connections, and apply a non-conductive coating if necessary
  • Oil motors and check belts for tightness and wear
  • Check the accuracy of the thermostat.
Source: Department of Energy

Essential Maintenance For an Air Conditioning Unit | how-tos | DIY
Maintaining Your Air Conditioner | Department of Energy
Air Conditioner Maintenance - YouTube
Air Conditioner Maintenance Kit $70

PSE&G's Cool Customer Program (Radio-shutoff):
PSE&G was installing grey boxes on the side of your compressor which would allow them to turn off your AC for up to 15 mins. twice in an hour via a radio signal.
Your fan would still run but just recirculate air without cooling.
They would do this in case their system was getting overloaded.
Since 2005, PSE&G has only initiated a total of eleven cycling events. A maximum of 3 events in 2008, 2011 and 2013.

As of 2015 they were not installing it on new systems.
See www.pseg.com/home/save/manage_costs/cool_customer/faq.jsp


BTU - British Thermal Units - A measure of energy. The amount of energy needed to cool or heat one pound of water by one degree Fahrenheit.

EER - Energy Efficiency Ratio - This number is less accurate than SEER because it doesn't account for fluctuations in temperature over the season.

Enthalpy - Enthalpy is the amount of heat content used or released in a system at constant pressure. Enthalpy is usually expressed as the change in enthalpy.

Enthalpy of Vaporization - Chemwiki - UCD - The kinetic energy of a gas is higher than the kinetic energy of a liquid. Heat provides the kinetic energy, heat goes into the gas as it is vaporized and remains there to keep the substance in a gaseous state. This lowers the temperature in the remaining liquid.

Expansion Valve - see TXV below.

HVAC - Heating, Ventilating, and Air Conditioning system.

PSIA - Pounds per square inch absolute.

Refrigerant - The liquid in your air conditioner's coils that make it work. The most common was R-22 (Freon). R-22 is a hydrochlorofluorocarbon (HCFC) compound, which contains ozone-depleting chlorine. The U.S. Environmental Protection Agency (EPA) has mandated the phaseout of R-22 through the Clean Air Act. As of 2010, the manufacture of systems using R-22 refrigerant will be prohibited, and by 2020 the production of R-22 itself must cease.
R-410A is the most common new refigerant. See Refrigerants below

SEER - Seasonal Energy Efficiency Ratio - High efficiency systems have a SEER of up to 24. To gain Energy Star status, a split-system A/C must have a SEER of at least 14.5

Split System - A typical home air conditioning system with one part (evaporator) inside inside and another part (condenser) outside.
The other type is called a packaged system.
See Identify My AC System | Aire Serv

TXV - Thermostatic expansion valve - Also called a TX or TEV valve. - A metering device that egulates the rate at which liquid refrigerant flows into the evaporator.

See alsoHVAC Glossary of Terms at ac-heatingconnect.com

The most common was R-22 (Freon). R-22 is a hydrochlorofluorocarbon (HCFC) compound, which contains ozone-depleting chlorine. The U.S. Environmental Protection Agency (EPA) has mandated the phaseout of R-22 through the Clean Air Act. As of 2010, the manufacture of systems using R-22 refrigerant will be prohibited, and by 2020 the production of R-22 itself must cease.
Newer systems use R-410A refrigerant.
R-410A cannot be used in a system designed for R-22 and they cannot be mixed..
Under U.S. regulations, chemical companies can continue to make R-22 for service needs until 2020, and may offer R-22 reclaimed from equipment until 2030.
HVAC equipment producers can manufacture R-22 HVAC repair parts as long as they are sold "dry," without the refrigerant.

Converting an R-22 system to R-410A is like converting a diesel engine to run on gasoline; it can't be done without making major changes to the entire system.
In the case of HVAC systems, conversion requires replacing the R-22 compressor, evaporator and condenser with units designed to run with R-410A. Sometimes the copper lines connecting the components also must be replaced, but it may be possible to clean, flush and dry the lines if they can handle the higher pressures of R-410A.

At some future point, though, system owners will find it more cost-effective to replace an old, breakdown-prone R-22 system with a new R-410A HVAC system.
Source: How to Switch an HVAC System From R-22 to a R-410A | Home Guides | SF Gate

Dry Charging:
While R-22 was outlawed in 2010 for use in new units, some companies are taking advantage of the law by producing what's known as 'dry charge' units. These are new units that don't have the refrigerant installed at the factory. Instead, a technician is required to come out to your home and install the R-22 refrigerant. While this practice is technically legal, this isn't the best option for the following reasons:

  • There is a limited supply of R-22 and its price will increase as supplies diminish
  • R-410A offers greater efficiency, saving you in energy costs, and is much better for the environment
  • Dry charged units typically offer much shorter warranty periods
The Difference Between R-22 and R-410A ac-heatingconnect.com
Cooling Refrigerants | Lennox.com
Central Air Conditioning: Understand How It Works
How to Inspect an HVAC System | Home Guides | SF Gate
Why is my Air Conditioner Freezing Up? And How to Fix it.
Pressure Enthalpy Diagram for the Mechanical PE Exam
Air Conditioning / Heat Pump Repair Guides - how to troubleshoot your air conditioner or heat pump
Air Conditioners & Heat Pumps: Diagnose & Repair Guide - how to fix an air conditioner or a heat pump
Test Your Central Air's Cooling Ability | Lowes.com
Boiler hot water Heating

last updated 3 Aug 2015