How do I fix my air conditioner?

Symptom:

The outdoor unit isn’t running but the indoor fan is blowing air.

Possible Causes (there’s a lot):

Power is off to the condenser (outdoor unit).

• Check the breaker panel to see if any breakers have tripped or turned off.
• Look near the outdoor unit for a service disconnect, an electrical box that houses either a breaker or, more likely, a disconnect that pulls out from the box. Ensure this is in the “on” position.
• Check the disconnect for fuses that may have failed.

The low voltage has been damaged or cut.

• Check to make sure someone didn’t accidentally hit the low voltage wiring with a weed trimmer or something. If this is broken it will not close the contactor.

The contactor may have failed. (The contactor is the relay that turns on the outdoor fan and compressor.)

• The relay may have failed, causing the switch not to close.
• The contacts could be “pitted” or damaged from use, no longer allowing electricity to flow across them.
• The wiring connections could be burnt, damaged, or otherwise not appropriately connected to the contactor.

The capacitor may have failed. (The capacitor is a device that stores and discharges electricity for use by the fan and compressor motors)

• The capacitor may be visibly “popped” or bulged, leaking oil, or may look just fine but no longer works internally. You can test the capacitance with a multimeter capable of doing so.
• The wiring connections could be burnt, damaged, or otherwise not appropriately connected to the capacitor.

Symptom:

System blows warm air. The outdoor unit makes a buzzing sound for a moment, but does not run. The indoor blower is running.

Possible causes:

The capacitor may have failed. This is the most common cause. (The capacitor is a device that stores and discharges electricity for use by the fan and compressor motors)

• The capacitor may be visibly “popped” or bulged, leaking oil, or may look just fine but no longer works internally. You can test the capacitance with a multimeter capable of doing so.

Winding damage. 

• Is it unlikely, but possible that the compressor and fan motor both may have damaged internal wiring from electrical surge or lighting strike.

High pressure switch.

• Some equipment models have refrigerant pressure switches installed to shut off the outdoor unit when the pressure in the system becomes too high.
• Ensure that the condenser coils aren’t plugged with grass clippings, cottonwood, or other debris.
• Test the pressure switch to see if it is electrically open. Compare the current refrigerant charge and the rating of the switch.

Low pressure switch.

• Some equipment models have refrigerant pressure switches installed to shut off the outdoor unit when the pressure in the system becomes too low.
• Check the indoor air filter. Poor airflow can cause colder temperatures, and this will cause lower pressures.
• Check that the indoor blower door is secure and that air is being forced across the indoor coil for the same reason as above.
• Test the refrigerant pressure in the system, it may have lost its refrigerant charge.
  

Symptom:

There is ice on the coil, copper line-set, or condenser. The system doesn’t cool and there is water around the indoor equipment. The blower is running on the indoor equipment, but no air can be felt out of the registers.

Possible causes:

Poor airflow.

• Check your air filter. A dirty filter will lower airflow and cause the indoor coil to become too cold.
• Check that the blower motor is running and that air is being forced to flow through the coil.
• The blower motor, capacitor, or circuit board may have failed, preventing the motor from blowing air at all
• The door panels or ductwork may be insufficiently installed causing air to bypass the coil.
• The airflow setting for the blower may be too low. 
• The blower may be running at a lower RPM due to age or seized. This can normally be heard (buzzing, humming) or smelled (burnt electrical “plastic-y” scent).

Dirty indoor equipment.

• The blower wheel may be dirty and no longer pushing enough air through the system.
• Some furnaces have a secondary heat exchanger that looks like a radiator on a car. It is mounted directly in front of the outlet of the blower assembly. This can become plugged with debris and restrict airflow.
• The evaporator coil itself may be dirty. The evaporator coil is the part that circulates cold refrigerant indoors. It normally “sweats” quite a bit due to humidity in the air. This makes it pretty easy for dust to stick to the coil, and can also dramatically reduce efficiency and airflow.

Low refrigerant charge. (Always verify airflow before adjusting refrigerant charge)

• Test the refrigerant pressure.

• Pressure and temperature are directly related. If the pressure in the system is too low, the temperature of the system will also be too low. Convert the suction gauge pressure to temperature. If that temperature is below 32° F (0° C), or “below freezing,” AND THE INDOOR AIRFLOW IS GOOD, then you likely have a refrigerant leak.

Failed/plugged metering device.

• Test the refrigerant pressure.
  
• A restriction within the metering device can reduce the pressure (and therefore temperature) or the evaporator coil. The suction line pressure and temperature will read low accompanied by an increased liquid line pressure. (This can also occur at a filter drier and other restrictions)
  

Symptom:

The system runs and cools well but there is water around the indoor unit.

Possible Causes:

Plugged condensate line. If the drain line leading from your indoor coil becomes plugged it can back up and begin spilling onto the floor.

• Sometimes you can remedy this by lightly tapping the line to break the restriction loose.
• Blow/suck the restriction out with a shopvac.
• Cut out and replace the drain lines with new. Flush the new drain lines annually with bleach or vinegar.

Cracked coil pan. Evaporator coils collect condensation on the fins, this rolls off and into the evaporator coil drain pan. If this plastic pan becomes damaged it can cause this condensation to leak onto your equipment and the surface below.

• Replace the coil pan. This process is difficult and sometimes parts are not available.
• Replace the whole indoor coil. This process requires specialized tools for refrigerant handling and an EPA certification to do so.
• Sealant. I’ve seen epoxy, Flex Seal™, and even silicone used to repair cracked drain pans, but the results are likely temporary.

It’s actually from something else near it.

• Sometimes the water heater, dehumidifier, or ice maker line are actually the thing that is leaking and it’s just close enough to the HVAC equipment that it appears to be the cause. I once saw a floor drain located under a furnace that was backing up, the HVAC equipment wasn’t even connected to it
  

Symptom:

The system runs constantly but it never gets colder in the building or struggles to keep up.

Possible causes:

Improper refrigerant charge. (Always verify airflow before adjusting refrigerant charge)

• Test the refrigerant pressure. The system could be so low that it’s not longer able to move heat.

Plugged condenser coils.

• Wash the condenser coils to ensure adequate airflow through them.

Compressor not running. The outdoor fan may be running, but the compressor isn’t.

• Test the refrigerant pressures to see if the compressor is running.
  
• Capacitor may have failed preventing the compressor from starting.
  
• Wiring connection on the compressor, capacitor, or contactor, preventing the compressor from running.
  
• The compressor may be internally damaged. Either free-spinning but not moving refrigerant, or mechanically seized and not moving refrigerant.

Poor ductwork/airflow distribution.

• Sometimes the system just wasn’t designed correctly. If this is a concern, a Manual J load calculation and Manual D ductwork design should be performed to determine the size of the equipment and amount of distribution and return air runs required. This is commonly seen on the second floor of two story homes and in additions.

Symptom:

“My upstairs, second floor, addition, or other room is not cooling down.” The system cools some areas adequately but not others.

Possible causes:

Blocked vents.

• Ensure all vents are open in the area.
• Ensure return air grilles are not blocked.
• Ensure that the vents are blowing air. Sometimes things like toys can be “accidentally” stuck into the vents, restricting airflow.

Equipment undersized or ductwork not adequate.

• Sometimes the system just wasn’t designed correctly. If this is a concern, a Manual J load calculation and Manual D ductwork design should be performed to determine the size of the equipment and amount of distribution and return air runs required. This is commonly seen on the second floor of two story homes and in additions.
• Sometimes the best solution for this is to install a secondary system in the trouble area, rather than trying to adapt the existing system, which could end up being major construction.
• Other times using a supplemental “booster” blower can forced more conditioned air into the space.
• Rooms with a disproportionate amount of windows or doors should be factored into these designs and compensated for.

Disconnected ductwork.

• If ductwork is disconnected it will be pretty hard to force air through it. Identify where the supply run connects to the main trunk, make sure it’s contiguous.

Poor insulation.

• If your ductwork runs through an unconditioned space (like a crawlspace or attic) and it’s not insulated it may be loosing its temperature conditioning through that space.
• If the room or space has poor insulation the heat load may be too high for the cooling system to keep up. This factors back into properly designing a system to accommodate the structure and may be as simple as adding appropriate insulation

This is far from an exhaustive list of things that could be wrong with your cooling system. Hopefully, however, it helped you solve your issues today, or helped you decide if this was even an issue you want to try to handle yourself. We also have not yet handled the process of testing individual components. We’ll save that for future articles.

If you have any questions regarding this article email us: hello@fixmyheat.com