Home air conditioning problems

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You'll find the common home air conditioning problems I describe below both easy to troubleshoot and often easy to solve.

Remember that, especially for a central air conditioning unit, you should have your system serviced annually by a qualified HVAC technician, and you should use such a technician to resolve any home air conditioning problems where the cause and solution are not both obvious.

• Air conditioner won't turn on
• Air conditioner cycles on and off frequently
• Air conditioner runs constantly but doesn't cool well
• Air conditioner runs but doesn't cool at all

Are you wondering why I provide troubleshooting tips for home air conditioning problems on a site dedicated to home energy efficiency?

Well, I want you to save as much energy as possible - it's my way of doing something to help stop climate change. One of the biggest home energy wasters is an air conditioner that isn't working properly. By helping you diagnose some of the simplest home air conditioning problems - and urging you to go to the pros when there isn't an easy diagnosis or solution - I can help you save energy by making your current system work properly, and help keep you from ruining a perfectly good system by trying to solve home air conditioning problems you're not qualified to solve. This bears repeating: Do not try to fix home air conditioning problems if you aren't sure you understand the cause, or the solution.

Air conditioner won't turn on

First check this...
Photo by jcarter, via FLICKR

Let's look first at home air conditioning problems with central air conditioners, then room units.

Air conditioner won't turn on - central air

For a central air conditioning system, the key things to look for are problems with power, fan, thermostat, noise, coolant pressure, condensate drainage, and startup time.

Power: Most central AC systems are on a separate circuit breaker, often a double switch. Many people flip this circuit breaker off at the start of the heating system, to prevent someone from accidentally starting the AC unit at a time when cooling is never needed. So check that this circuit breaker is turned on. If it is turned on, turn it off then back on (sometimes the switch has tripped but is close enough to the on position that it seems to be on already). This is one of the most common home air conditioning problems according to technicians who write on the web - so check your circuit breaker!

In many jurisdictions, a breaker may be required within a short distance from the outdoor compressor unit. If you still can't get power to the compressor, check for this circuit breaker either inside your house near where the wiring exits the house, or on the outside of the house near the compressor unit. Try flicking that breaker off and back on as well.

If either the panel breaker or the compressor breaker circuit trips off after you try using the AC again, don't flip it back on - call a qualified technician. There may be a serious electrical problem that needs to be looked at by a pro.

If you have a combined central AC and forced air furnace system, the circuit that feeds your furnace should also be on, as the furnace fan needs to run to circulate the cooled air. Check this circuit as well, using the same process of turning the breaker off and back on. The furnace circuit could be controlled both by a circuit breaker on your breaker panel, and possibly by a wall switch in the furnace room. Check both. I have such a wall switch and use tape to keep it in the correct position (on during heating/cooling season, off in spring and fall), to prevent someone from mistaking it for a light switch and accidentally turning it off during the heating/cooling season.

Another thing to check is that the fan is running. If you set the fan setting to "on" instead of "auto", you should hear the furnace fan start to run even if the air conditioner doesn't turn on. If the fan doesn't turn on, this is an indication no current is getting to your furnace.

Then check this...
Photo by superstructure, via FLICKR

Try setting the thermostat as low as it can go (remember to turn it back afterwards!). It's possible that the thermostat controls are not working properly. I once had a home air conditioning problem where the only way to get the AC on was to turn the thermostat down to 49F (9C)!

If your thermostat is a programmable thermostat, check that it shows some indication of being on! If you can't see anything on the LCD display, there may not be any power getting to the thermostat. This could be because the DC line powering the thermostat is off, or because the furnace is switched off.

Remember that when you are running the AC your windows and doors tend to be (and should be!) closed. Make sure your home air conditionig problem isn't just that the closed doors and windows are stopping you from hearing the noise of the compressor running.

In some central air units, the compressor (outdoor) unit has a high pressure cut out, which stops the unit if the coolant pressure gets too high. This is a button that sticks out of the cabinet, near the coolant lines. Press this button in to reset it. If the button pops back out soon after the unit starts up, call a technician to have the refrigerant level checked - this is not a home air conditioning problem you should try to solve yourself.

Then get out the gloves...
Photo by prettywar-stl via FLICKR

The evaporator unit in a central air conditioning system needs to drain condensed water that collects on the coils. Two common air conditioner problems here are that the condensate drain may be blocked, or, if the system uses a condensate pump, the pump is not working. If condensate is not properly draining, check that the condensate drain is clear and that water can flow freely down it, and if the system has a condensate pump check that it is plugged in and working. The unit will not run until this home air conditioning problem with condensate draining is fixed.

Finally, be patient. Sometimes it can take a minute or two for the compressor to start up. If the system routinely takes a long time to start up, have your unit serviced.

If none of these tips solve your home air conditioning problem, call a technician. Don't try to solve a home air conditioning problem yourself if the cause is not obvious. You could cause a lot of damage to your AC system, or risk electrocuting or otherwise injuring yourself, by tinkering further than what's suggested above.

Room air conditioner won't turn on

Check for obvious causes of this home air conditioning problem: is it plugged in? Is the outlet live? Has the selector switch inside the unit tripped?

To check if the outlet is live, plug in a lamp or other device that indicates power. Remember that a room air conditioner draws a fair bit of power and if your house is poorly wired or there are several high-amperage loads on the same circuit, the air conditioner or some other device may have tripped the circuit. Check the circuit breaker panel if the outlet appears dead; flip the circuit back on if it is of. If turning on the AC unit causes the circuit to flip off again, do not reset it - there may be a short in the window unit, or there may be a problem with your house wiring. Try plugging the AC unit into a different outlet where you know there are no other loads on it and the amperage of the circuit is adequate. If it trips that circuit, it is likely a short in the unit and the unit needs to be repaired or replaced. If it does not trip the other circuit, the original circuit may be too low amperage, or may have other loads that are consuming too much power (perhaps another AC unit, but in that case neither would be working!).

Check for a tripped selector switch or broken or corroded internal wiring on the window unit. First, unplug the air conditioner, then check that you really unplugged it! Your window unit should have a selector switch close to where the power cord enters the unit. Remove the front panel from the unit and check that the switch has not tripped. If it has, try flipping it back on, replace the cover, plug the unit back in, and try running it again. If it trips again, this is not a home air conditioning problem you can fix yourself; the unit needs to be serviced. Also (again, after unplugging the unit) check for any frayed or loose wires. Have the unit serviced if you see any loose wires or signs of corrosion or burning or exposed metal along insulated wires.

If your unit has a dial to control temperature, check that turning the dial actually turns the control it attaches to. If the dial can turn continuously for several revolutions it is probably not turning the underlying control.

Beyond these simple, easily diagnosed home air conditioning problems, a room air conditioner not turning on means it's time to get it serviced. If the unit is more than five years old, shows signs of corrosion on the fins, or was a cheap, inefficient air conditioner to start with, you are probably better off buying a new energy efficient window ac unit instead of paying to have the unit serviced.

Air conditioner cycles on and off frequently

A unit that cycles on and off frequently can be an indication of a unit that is oversized for the cooling work it needs to do, or an indication that the thermostat is being directly cooled by the unit or by a cooling register.

If your unit has always cycled frequently, oversizing is likely the cause of this home air conditioning problem. An oversized air conditioner cools the air conditioned space rapidly, so that the thermostat shuts the unit off quickly. The air conditioned space may warm slowly or more quickly depending on insulation, outdoor temperature and other factors, but typically an oversized system will cycle on and off with short periods where the compressor runs, and longer periods where it does not.

If the unit started cycling frequently in the last few days, there are three possibilities: you are cooling less space than you used to (and have thereby made the unit 'oversized' for the work it's now doing); there is poor air circulation around the coils and so they are icing up, causing the unit to shut down until the ice thaws; or there is a problem with the refrigerant.

A space can suddenly become oversized if you have closed off a portion of the space. For example, if you have a central air conditioner and you decided to close off the registers in rooms that aren't used (such as spare bedrooms), the air conditioner may be short cycling because it is cooling the remaining rooms too quickly. If you have a room air conditioner that you moved from one room to a smaller room, or you used to use the unit with the room door open and now the room door is kept closed, you have essentially made the unit cool a smaller space and it may be oversized for that space.

Rapid cycling can also be caused by refrigerant problems such as low levels of refrigerant (which usually means a leak), too high a level of refrigerant (which usually means it was overcharged when the system was installed or last serviced); or the wrong type of refrigerant. If you are unable to determine another cause for short cycling, call a professional to have your unit's refrigerant level checked.

Other possible causes of short cycling are clogged or dirty coils, dirty or damaged fins on the condenser unit, or damage to the condenser unit motor or blade. If you're reasonably competent with do it yourself maintenance you can try to investigate each of these possibilities, but don't take any chances if you're not sure what you're doing. The pros often get called in for home air conditioning problems the homeowner has made worse by trying to solve themselves!

Air conditioner runs constantly but doesn't cool well

A common home air conditioning problem is the always-on air conditioner. This can indicate an undersized air conditioner, which is simply unable to cool the house; it can also indicate an extreme difference in temperature between the outdoor and indoor air. If your air conditioner is running constantly and there's an extreme heat wave, don't be too surprised. It's better to be uncomfortable a few days a year with an air conditioning unit that is correctly sized for typical conditions, than to install an oversized air conditioner that can handle the extremes, but have the unit short cycle and wear itself out on more moderate days.

One easy test is to see if the air conditioner is producing cool air, or any air at all.

For a central air unit, can you feel cold air blowing out the vents? If the unit is running constantly but airflow is weak, you may have a problem with your ventilator fan, your ductwork (excessive air leakage in the ducts, excessive dust or debris buildup, damaged ducts), the AC or furnace filter, or something as simple as a duct baffle that has not been switched from the winter to the summer position. Check for each of these as possible causes.

If you have not had your ducts cleaned in more than a year and dust is visible when you remove heating registers, it is probably time to have your ducts cleaned again. If your ducts are leaking or damaged, you should have them repaired; this will save you much of the electricity your air conditioner now uses.

Check the ducts around your furnace and look for a baffle lever with 'summer' and 'winter' or 'heat' and 'air' indicators - sometimes just written in permanent marker on the ductwork. Make sure the baffle is in the summer position. If that doesn't solve the airflow problem, call a technician for a professional assessment.

If the airflow is good and cold air is coming through the vents, the probable cause of this home air conditining problem is poor insulation or air leakage in the rooms being cooled. The air conditioner is working as designed but too much heat is flowing in from the outside, giving the air conditioner an impossible task

The location of your compressor (outside unit) may be a factor in how efficiently a central air conditioner, or indeed a window air conditioner, cools your air conditioned space. If your central AC is buried underneath a porch so that air flow is severely restricted, you will get little to no cooling out of it. (This may sound like an impossible scenario - but it's how my own AC system came when I bought the house, because they installed the compressor unit in the garden, and later built a back deck over it!) Hire an HVAC company to move the compressor unit out into the yard where it has better air flow.

For a window air conditioner, if the outside of the unit is near a heat source (such as the hot exhaust from a neighbor's central AC compressor or the heat radiating off a hot roof) or is exposed todirect sunlight, it will be far less efficient than if it is in a shaded area with good air circulation.

Air conditioner runs but doesn't cool at all

If the airflow is good and the air coming out is not cold, your home air conditioning problem may be a temporary problem - your coils may have frozen. Turn the unit off for an hour to let them thaw, then try again. If cold air is now present, freezing coils were the problem; if the problem recurs soon after turning on, you may need to replace the coils. Again, call a pro. If you have ceiling vents in upstairs rooms and the air flowing from them is consistently warm, you probably have leaky or poorly insulated ductwork in your attic. See my Attic ceiling insulation page for more information on insulating ductwork that runs through attics.

Another likely home air conditioning problem if you have good airflow but no cooling is that the breaker to the outside unit is shut off, which depending on the installation can either cause the air conditioning system to not run at all, or to appear to be running but not provide any cooling. If you can hear the compressor fan running outside, the breaker is on, but if the outside unit is silent the outside breaker may be off. If switching it on does not solve the problem, look for the high pressure cut out on the condenser and try resetting that.

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