Air Conditioning Tips

To help you stay cool and save money by keeping your A/C running at peak performance.

This information will help you stay cool and save money by keeping your Air Conditioning running at peak performance. It will assure your HVAC system is keeping you as cool as possible, working efficiently while saving you money. Will also help you decide if you need a professional to repair or service your Air Conditioning system.

(1) Air filter(s) MUST be clean.

Filters are located in the return air duct adjacent to the air handler or in a return air grill(s) in your wall or ceiling. Check your air filter every 30 to 90 days to make sure it is clean. Depending of the house, i.e. if you have animals you may need to clean or replace the air filter(s) more often. (Go clean them now!)

(2) Flip the switch or push the button on the thermostat for the fan setting to FAN ON, not AUTO.

This will run the indoor fan nonstop. The outside A/C unit will still cycle with a call for cooling from the thermostat. The constant air moving will keep you cooler. You can probably keep the thermostat a degree or two higher than normal and still feel comfortable. You will also maintain a more even temperature between upstairs and downstairs. This will SAVE you MONEY because the outdoor condenser will not come on as much!

(3) Make sure you wash the outside condenser coil once a year.

If it's dirty the A/C will run hot and inefficient. A sign of the coil being dirty is the small exposed copper pipe (tubing) line, usually 3/8" O/D connecting the inside unit with the outside unit will be HOT to the touch.

(4) If the small exposed 3/8" copper pipe is hot

If the smaller of the two copper tubing pipes connecting the inside unit with the outside unit is hot to the touch there can be several reasons why. These are the two most common reasons for the pipe to be hot to the touch.

(5) Warm Rooms

On the lower levels of the house where it is cooler cut back / partially cut off some vent registers (Diffuser) but do not close them off all of the way, doing so could interfere with the static air pressure (air balancing of the system.) Make sure all the ones on the upper floors where it is warmer are open all the way! Also, see paragraphs #2 & #9.

(6) Doors Need An Airgap

If you close the door to a room make sure there is about a 3/4" gap between the bottom of the door and the floor. You may have had carpet put down on the floor and now there is no gap. This is necessary if you have a central return air duct in the hallway. The return air ducts need to pull the warm air from the room.

(7) Should I turn the A/C off when I leave the house?

You can set the temperature up five to ten degrees, but never leave the house and turn the A/C off. If it is a hot day when you get back home and turn the A/C on it could take several hours or all night to cool your house down. This is because the heat buildup in the walls and furniture in the house and will make the A/C work harder to remove the heat, this takes a very long time.

If you are going to be gone for a couple days or longer, then you can turn the A/C off, but keep in mind how hot you might get, I've seen candles melt, and there are many other considerations, pets, furniture and art, etc. (edited 09-11-23)

(8) Never turn the A/C off than back on in less than five minutes

This will short-cycle the compressor and can trip breakers, blow fuses, or cause permanent damage the compressor. You should have a time-delay install on the A/C to prevent this during power outages! Most digital programmable thermostats have a time-delay of 3-5 minutes built-in. Having a start capacitor and relay is a good idea. This will increase the life expectancy of the compressor by starting faster thus keeping motor electrical windings temperature down, using less electric to start.

(9) Keep blinds closed, curtains drawn, window shades down.

A working attic fan would be a good idea. Plenty of insulation in the ceiling & walls. Air tight storm windows. Keep outside doors and openings close, etc.

(10) Ceiling or other fans are a good idea, they can keep the air moving and make you feel cooler.

Ceiling fans also help with keeping the temperature more even between the floor and ceiling. Note: during the summer ceiling fans should be blowing the air in the downward direction, but in the winter you would reverse the air direction to blow upwards and at a much lower speed.

(11) Icing of the indoor coil or the large insulated covered copper pipe.

There are two main reasons for this, lack of air flow or low on refrigerant. Lack of air flow can be a dirty air filter, dirty indoor evaporator coil, dirty fan blades, damper in duct restricting air flow.

(12) Water inside around air-handler.

The condensate line is a drain pipe coming from the indoor evaporator coil to an indoor drain or to the outside. This can become clogged and cause water to backup and can produce about five gallons of water an hour. This is where all the humidity and moisture from the house goes. This is usually a 3/4" white PVC plastic pipe.

(13) You should NEVER need to add refrigerant (Freon) to a system.

If you are adding refrigerant this means there is a refrigerant leak in the system that NEEDS to be fixed! (Why KILL the Ozone layer?) and running your system low on refrigerant can cause damage.

(14) Checking the cooling with a thermometer.

There should be a 15-20 degree (Delta-T) temperature drop across the indoor coil at the air handler. Check the temperature drop in the duct close to the coil, if air coming into the coil is 75 degrees than the air leaving the coil should be 60-55 degrees. If it is higher or lower there is probably something wrong. Too high of a drop, IE more than 20 degrees drop, could mean lack of air flow or low on refrigerant. Less than a 15-degree drop could mean too much air flow, dirty outside coil or low on refrigerant.

(15) Never cover the A/C (Outside unit) with plastic or an air tight cover.

This will cause it to rust. If it is a Heat Pump, it must remain uncovered with good airflow around it year-round, as it needs to run for both cooling and heating. 

(16) Do not let animals urinate on the outside coil.

If Dogs or Cats urinate on the unit outside, this will cause it to corrode and then leak refrigerant.

(17) Keep grass, leaves & weeds from blocking air flow on the outside A/C.

(18) Do not build a deck close to the top of the outside A/C

Or anything else that could cause the warm discharge air to re-circulate back to the unit. If you need to have the unit under a deck, they do make units that have side air discharge.

(19) Fuses, Circuit Breakers and wires should never be hot to the touch.

If they are hot you may have a sizing problem or a loose or bad electrical connection.

(20) Why do I have ice on my air conditioner.

Most common cause if a lack of airflow across the indoor coil, which can be cause by a dirty air filter, dirty fan blade, or other issues that is restricting or reduce the airflow. The other common cause is the system is low on refrigerant, if the unit is low on refrigerant, you have a leak that needs to be fixed. You should never need to add refrigerant, doing so is a temporary fixed, you need to find and fix the leak. (added 07-25-14)

(21) When you need to have your equipment repaired or serviced.

Make sure you use a licensed contractor who is certified by the State Board of Contractors, the Department of Professional and Occupational Regulation.

In Virginia you can use the DPOR website to lookup a contractor to see if they are licensed.

the contractor should be licensed, have bonds or insurance and obtain permits when required from the local municipality. DO NOT get the permit in your name, make sure the contractor gets the permits in their business name, using their contractors license, that way the Government holds the contractor responsible to for the work. If you have the permit in your name, YOU are responsible to the Government, not the contractor. (edited 09-11-23) 

(22) Air Conditioners DO NOT add cool air.

What they do is transfer warm air from the inside to the outside. R-410A, R-22 or R-12 etc. Refrigerant is a manmade product invented by DuPont and given the trade name FREON.

Warm air travels towards cool air. So saying close the door I am trying to keep the heat out would be correct. Warm air rises.

The temperature of refrigerant is directly relate to the pressure it is at and vise versa, example, R-22 at 0 psi is -40 degrees below zero or at 60 psi it at 32 degrees. This is misleading; the temperature change is NOT related to pressure really, but almost totally tied to the change from a liquid to a gas. When liquid Refrigerant is expanded to a gas it gets really cold (latent heat of evaporation) and when the warm gas is compressed to a liquid it gets hot. The temperature change in say compressing liquid Freon to a higher pressure (adiabatic compression) is small. You see the same effect when you crack the valve on a CO2 or propane bottle for example. You will get a smaller effect with a pure gas, like when you fill a Scuba tank it gets warm or drain it quickly the valve gets cold right at the expansion point, but this effect is not great enough to run an AC system.

The physics of phase change from a gas to a liquid and vice versa drives most weather as well, for example.... With water it takes as (I recall)  560 (or was it 590...) times as much energy to boil water from 100c liquid to 100c gas as it does to raise the same amount of water 1c in temperature. Freon is less dramatic than water in terms of this energy amount, but it boils at a much more convenient temperature for human AC units than does water. If you wanted the inside of your house to be 100c you might want to run water in your AC.

(23) FYI only.

All the A/C compressor does is pump vapor to create a high and low pressure, ie. A low pressure at the inside coil for a low temperature for the refrigerant to absorb the heat in the house and a high pressure at the outside coil to give off the heat the refrigerant absorbed from the inside coil to outside. Over sized A/C will run short cycles and not remove the humidity and moisture from the house, an under sized unit will not be able to keep the house cool on a hot day. You MUST be careful to get the correct size A/C for your house. A/C's are sized by tons; there are 12,000 BTU'S to a ton of cooling. ("Ton" means 12,000 BTU'S of heat is needed to melt one 1 ton (2,000 Pounds of ice) You need to move 400 CFM of air per ton of cooling across the indoor coil. 450 CFM for Heat Pumps. Each CFM (Cubic foot per minute) of air will carry 26.7 BTU's of cooling. You need a heat-gain calculation done per room to get the proper (CFM/BTUs) to be delivered to each room and the total (Tons/BTUs) needed to cool the house based on designed weather conditions in your area.

The above is my personal opinion and advice, based on 15 years of my experience (as of about 1994) in the Plumbing, Heating, Cooling business. Please feel free to obtain other opinions as I may have got something wrong. (I am sure if I did you will let me know)

William J. Baumbach II
President. Baumbach Enterprises Ltd. (until about 1993) President of the Northern Virginia Plumbing, Heating, Cooling Contractors Association (PHCC) in 1996 & 1997.

Historical info

In 2013 this page got so many visitors, Google emailed me to alert me. over 5k per month.

These A/C tips were originally published on a Bulletin Board System (BBS) that I ran, computers that connected to each other over dial-up modems using a phone line, before the internet.

Air Conditioning Tips, original prior to 1995. Edited 07-17-2010 Edited 03-25-12 Edited 07-25-13 Edited 07-25-14 Edited 10-25-14 Edited 09-11-23 (moved site and made some edits)