Most Common Central Air Conditioner Problems And Repairs Needed

Central Air Conditioner Problems:  In previous Blog Posts, we have discussed proper maintenance of your HVAC system.  If you are doing that, breakdowns will be notably reduced. However, Central Air Conditioners will stop working, due to problems or components that wear out and fail, that are not related to maintenance.

Below Are The Most Common Central Air Conditioner Problems (which cause it to stop running):

There are some common Central Air Conditioner Problems most homeowners can check and correct. They are related to No Power, Thermostat Settings, Cleaning the A/C drain line from the furnace, and Thawing a frozen a/c coil (inside the furnace).

Beyond these, we don’t recommend home owners try to do a/c repairs.  You may create bigger problems or injure yourself.   HVAC Technicians are trained to troubleshoot your air conditioner, determine what the problem is, then make the repair with the correct part and installation method.

Central Air Conditioner Problems: NO POWER   This are 4 homeowner-correctable “No Power” problems.


Central Air Conditioner Problems: GAS Furnace Main Furnace Shut Off Switch Is Turned Off becoming turned off is one of the common central a/c problems.  This switch is located on or near the GAS furnace and shuts down the entire system.  The switch must be turned on.  It’s often easy to bump this switch when changing the filter.  Also, curiosity can encourage someone to turn if off (to see what happens) and not turn it back on.

Central Air Conditioner Problems: ELECTRIC Furnace Circuit Breaker (near the furnace) has tripped or is turned off has a is a circuit-breaker on or near the inside unit.  The breaker shuts down the entire system.  As with many breakers, it may be tripped but not appear to be. Flip the breaker to off, then back on to reset it.

electric furnace indoor shut off switch  Electric Furnace Indoor Disconnect Switch

FURNACE CIRCUIT-BREAKER  tripped circuit breaker Breakers at the Circuit Breaker Panel

Central Air Conditioner Problems: Circuit Breaker (inside the Circuit Breaker Panel) is tripped or turned off —  Turn It On.    Tripped circuit breaker — Reset To On.  Note: It may not appear to be tripped (see breaker #13).

Central Air Conditioner Problems: Blown Fuse In Outside Fuse Box (near the outside a/c unit).  This may be the problem in older homes with fuse-boxes.

Before central a/c problems repairs begin, the outside disconnect box is shut off to protect a/c service technicians.  If the primary breaker or fuse (inside the home) is not within view, Building Code requires the disconnect box to prevent electrical hazard to a technician in the event someone turns the breaker inside the home back on.

Additionally, these fuses provide another degree of protection for the outside unit. Outside fuses are used for overload protection. These fuses are typically sized to the specific load they protect, and may be a lower size than the circuit breaker in the main breaker-box . If a fan or compressor cannot spin (most newer a/c compressors spin to compress refrigerant) it will quickly overload, overheat, and burn up. The fuses in the a/c disconnect prevent this from happening.

Note:  Never put a higher rated fuse (than is specified) in the outside disconnect box.  The larger fuse will allow the a/c to damage itself, instead of blowing to prevent it.

Central Air Conditioner Problems: Thermostat Not Set Correctly.   The thermostat tells the system to cool or heat, and to what indoor temperature.  A common central a/c problem results from the the thermostat not turned to the correct “Cool” setting -and- the thermostat is set lower than the indoor temperature.

Note: There is another switch for the (blower) fan.  It shows “Auto” & “On” settings — leave it set to “Auto” year round.

manual thermostat

Central Air Conditioner Problems: Clogged Drain line  One of the most common central a/c problems is a clogged drain line for removed humidity.  As your a/c runs, air is passed over a cold coil (located inside the furnace and not visible — see 2nd photo below.  This cold coil removes humidity from the air, which is then drained to the outside.

Over time, it is common for the drain-line to become clogged.  If it is clogged, the drain pan will overflow and cause water to leak out of the furnace at its lowest point. Water is then discharged somewhere within the house.

water damage from clogged a/c condensate line

Water-damage from clogged A/C Condensate / Drain Line.

diagram of a/c condensate pan and drain line

Cleaning a clogged condensate / drain line.

Central Air Conditioner Problems: Frozen evaporator coil (inside the furnace and not visible)

frozen air conditioner evaporator coil

If air-flow is reduced (often due to a dirty air filter) the coil inside the furnace can freeze.  If your furnace blower motor is running, but there is no air coming from the vents, it’s likely the coil inside the furnace is frozen.  To correct this, turn the a/c off at the thermostat and turn the fan to “on” at the thermostat.  This will being to thaw the frozen coil inside the furnace.

If air starts to flow from the ducts after 15 minutes, the coil was frozen.  Continue to let the fan run (with the a/c turned off) until the air volume from the ducts is what you typically have. At that point, you can turn the fan back to auto and the a/c back on.

Note: If the coil freezes, there is a problem and the coil will freeze again if the problem is not corrected.  Replace the filter if the filter media is no longer white, or visible dirt build-up is present.  If the filter is clean, there is another reason the coil froze, most likely it’s because the a/c is low on refrigerant.


Is your furnace blower running, but warm air is coming out the vents?  First, check to see if the outside unit is running (the furnace blower will run whether the outside a/c unit is running or not).  There are several reasons why the outside unit is not running.

One reason can be due to no power to the outside unit.  We addressed what a typical homeowner can check regarding “no power” issues early in this post.  If you have checked those, and they all seem to be ok, it’s time to call an HVAC repairman to determine what’s wrong with the outside unit.  There are many things which can fail. We have outlined the most common failures below.

Central Air Conditioner Problems: Failed Contactor  There are 3 Contactors:

  • For the Compressor
  • For the Condenser (outside unit) Fan
  • For the Furnace Blower Fan

The contactors engage to make an electrical connection at the start of the cooling cycle.  Over time, these contactors may fail as a result of normal wear & tear.  Failed contactors must be replaced in order for the a/c to run.

a/c compressor contactor

This is an A/C Contactor.  They will look different based on A/C brand /model, or Contactor brand / model and type of contactor (compressor, fan, blower).


Central Air Conditioner Problems: Failed Capacitor  The RUN Capacitor helps fan motors run at a consistent speed.   The START Capacitor gives the compressor a brief increase electricity to Start the compressor.  If a capacitor burns out, it must be replaced in order for the a/c to run.

central a/c compressor capacitor

This is an A/C Capacitor.  They will look different based on A/C brand /model, or Capacitor brand / model and type of capacitor (compressor or fan).

The Compressor Start Copacitor is responsible for giving the a/c extra electricity at start-up, then reduce the electricity to what is needed while the compressor is running.


  • Watts required to Start a 3 ton a/c = 4,800
  • Watts required to Keep a 3 ton a/c running after start-up = 4,350 watts


Central Air Conditioner Problems: Refrigerant leak   If you notice your a/c is running more than in the past, or your electric bills increased notably, your a/c may have leaked some refrigerant and is now low.  Without the correct amount of refrigerant, your a/c will run, but can’t cool at its peak ability.

Refrigerant leaks can happen at any location where refrigerant flows while the a/c is operating.  Refrigerant leaks in the Condenser Coil (outdoor unit) or Evaporator Coil (inside the furnace and not visible) cannot be repaired, and the component must be replaced.  For leaks in other locations, the technician can repair the leak and recharge the system with refrigerant.

Note: If your a/c is older and uses R-22 refrigerant (freon), recharging it will be very expensive in the near future, and not possible after that. R-22 refrigerant is no longer being made (it damages the Ozone-Layer).  Remaining supplies of new R-22 are priced quite high, and the only remaining source of additional R-22 is is “reclaimed” (removed from old a/c or refrigerators before they are disposed of).

Condenser Coil

The Condenser Coil is located in the outside unit. Here, you can see the silver coil through the housing’s openings.

furnace with evaporator coil showing

In this photo, the panel over the Condenser Coil has been removed to show the Evaporator Coil inside the housing above the furnace.  The white pipe is the drain line.


Central Air Conditioner Problems: Condenser Coil Needs Cleaned  This coil is located in the outside unit (with the compressor). During normal operation, the coil gets clogged with dirt as a result of pulling in large amounts of unfiltered air to cool the condenser coil.   The coil must be cleaned at the beginning of each cooling season for proper operation.

This can be done with a water hose when the a/c is turned off.   If the dirt gets bad enough, an HVAC technician will have to clean the coil with a chemical cleaner.  Al’s Plumbing, Heating and Air Conditioning offers an annual A/C Tune Up which includes cleaning the condenser coil.

Condenser Coil Before and After
Extremely dirty Condenser Coil before & after cleaning.


Central Air Conditioner ProblemsEvaporator (cooling) Coil Needs Cleaned.  Residential central air conditioning has the evaporator coil inside the furnace (photo shown earlier).  The coil should be checked annually and cleaned if needed.   A dirty evaporator coil is a perfect environment for mold to grow — with the blower motor sending mold-spores all over your home.

low refrigerant level system tun up
This very dirty Evaporator Coil has visible black mold growth present.

SUMMARY:  The Blog Post provides good insight into the most common problems and failed components which cause your a/c to stop working.  A trained HVAC Technician can diagnose what the problem is and fix it with correct parts and part-installation methods.

Al’s Plumbing, Heating and Air Conditioning maintains, repairs and replaces air conditioners, heat pumps and furnaces.  Call for an appointment to get your a/c working again.  Also, Al’s can ensure your A/C is running at its peak ability by performing all required maintenance.

Note:  R-22 (freon) refrigerant damages the Ozone-Layer, so it’s production has recently been stopped.

If you have an older R-22 A/C which is working well, you do not need to replace it simply because it’s an R-22 system.  Non leaking R-22 A/C pose no threat to you nor the environment.

It is worthwhile to say, however, your old A/C may be costing twice as much to operate as a new SEER-14 A/C.  If your current A/C was built before 1992, it may be using as much as twice the amount of electricity as a new SEER-14 A/C to produce the same amount of cooling.   Many A/C’s have the SEER rating shown on the silver tag on the outside unit.  If yours does not, you will be able to find its manufacture date and compare to the chart above.  Replacing an A/C built in 1992 or later, just for the increased efficiency won’t likely give you a payback over the life of the new A/C.


SEER Rating History

If your current a/c was built prior ot 2010, it likely is an R-22 (freon) system. Not all were, though.  R-22 a/c cannot be converted to R410A, the system must be replaced due to the possibility of some R-22 remaining which will damage the new components designed for R-410A.

The silver tag on the outside unit will tell you which refrigerant the system uses.

r-410a refrigerant a/c tag  This a/c uses R-22 / freon (see middle of tag about half way between top of tag and bar-codes)

r-22 refrigerant a/c tag This a/c uses R-410A (see right side of tag, just under 4th dividing line.

Note: Before you agree to costly repairs to an older R-22 (freon) refrigerant A/C, keep in mind that R-22 is no longer being produced.  In the near future, you will not be able to recharge your old a/c with R-22.  For repairs below $500 (if the a/c has not needed a number of repairs in recent years) you can certainly buy yourself some time by having your existing a/c repaired.


Al’s Plumbing, Heating & A/C maintains, repairs or replaces ALL brands of air conditioning, heat-pump, gas or electric furnace.  Al’s also provides new, installed HVAC Systems from:

  • American Standard
  • Ameristar (made by the same company as American Standard HVAC)
  • Coleman HVAC (made by the same company as York HVAC)

Call Al’s today to make an appointment for Central A/C Maintenance, Repairs or Replacement.