AC Problems – Ten Most Common Problems & Their Causes

ac problems and causesHere’s our run down of the ten most common AC problems & causes. There are roughly two dozen issues that can cause AC problems. Many of these are easy enough to fix yourself. This list will help you do it yourself before deciding to call in a pro.

1. AC system not turning on at all.

This problem has numerous possible causes all listed below. We have a page dedicated to the AC not turning on. It will walk you through everything you can check yourself:

* Electric Panel – Tripped breaker or blown fuse
* Thermostat not switched on
* Components not all plugged in or switched on
* Disconnect not pushed in or has blown fuse
* Clogged air filter
* Thermostat has wiring issue or has failed
* Condensate drain line is clogged or float switch is bad
* Bad capacitor
* Blown transformer
* Burned fuse on circuit board
* Circuit board failure
* Bad relay
* Worn electrical contactor
* corroded, burned or loose wiring
* System Low on Refrigerant Due to a Leak

2. AC turns on & blows air but doesn’t cool (ice around evaporator coils)

There are several causes for an AC running but not cooling. Most common cause is a dirty air filter or condenser coil (outside unit). Air filters should be inspected or replaced every 1-3 months. Condenser coils should be cleaned at least once per year. Dirty filters & condenser coils reduce airflow and can cause the evaporator coils to freeze.

If the fan and compressor both run, then it’s likely this is the cause. Otherwise there may be a refrigerant leak. If the compressor doesn’t turn on then you need to check the wiring & capacitor.

*dirty air filter
*dirty condenser coils (outdoor coils)
*low refrigerant/refrigerant leak
*compressor failure
*capacitor failure
*burned/corroded wiring to compressor or capacitor
*too hot outside for system

3. No air Flow from vents (compressor turns on but outdoor fan not running)

When no air air is flowing from the vents, but the compressor runs then it’s a fan problem. The following items will cause a fan to malfunction. See here for more details on how to fix an AC fan motor not working.

* Electric Panel – Tripped breaker or blown fuse
*fan motor failure, worn bearings
*fan motor dirty or not lubricated
*fan control board failure
*worn, broken blower belt
*capacitor failure
*fan wiring corroded, burned or loose

4. Low air flow from vents (& high energy bills).

The AC runs & cool air comes out the vents but the airflow is weak. Dirty air filters & leaky ducts will cause this air flow problem. This overworks the AC system and causes it it to run for longer.

*leaky ducts
*dirty air filter

5. AC keeps running without ever turning off.

If the system never stops running there’s several possible causes. Is just the fan always running or the compressor as well ? If just the fan then it could be a faulty fan relay or fan control board. If both run then it could be any of these other causes.

First check if the air filter & coils are clean, then check the fan is running at normal speed. A fan running at low speed can cause this. It can also be a refrigerant leak or faulty thermostat.

*dirty air filter
*dirty condenser coils (outdoor coils)
*dirty evaporator coil (indoor coils)
*fan motor malfunction (fan running at low speed, possibly due to faulty motor or control board)
*dirty fan – dirt & grime caked onto a fan blade can slow the fan speed.
*faulty fan relay
*low refrigerant/refrigerant leak
*leaky ducts
*undersized system doesn’t have enough BTU’s for square footage
*thermostat malfunction

6. The unit turns on and off constantly.

This problem is referred to as short cycling. It’s usually caused by a dirty filter or condenser & may be accompanied by a frozen evaporator coil. A refrigerant leak is another common cause.

*dirty air filter, condenser or evaporator
*low refrigerant/refrigerant leak
*oversized system (new install only)
*thermostat located too close to air vent (new install only)

7. The breaker keeps tripping.

*dirty filter and or condensor
*worn breaker
*capacitor failure
*condenser fan failure or improper grounding
*low refrigerant/refrigerant leak

8. Unit leaks water (outside or in ceiling).

The system has a drain line & sometimes a pump for draining out condensate water. If a drain line gets clogged the water will back up and fill the pan. There’s usually a float switch which will shut off the system when this happens to prevent water overflowing & leaking out into the ceiling. If the pump or switch are defective there could be leaking. See here for more on checking the float switch.

*dirty/clogged condensate drain line
*leaking condensate drain line connection
*condensate pump not working
*float switch defective

9. AC makes a strange noise or smell

Worn or loose parts or limited airflow overworking the system can cause noises or odors from friction.

*worn belt (squeek)
*worn motor bearings (grind)
*loose vent covers (rattle)
*loose wiring
*dirty filter

10. rooms are not equally cooled

This can happen because some rooms are exposed to more sunlight. The vents need to be adjusted for better balance. Use the levers on the vents to open or close the vents more. Warmer rooms stay fully open & colder rooms partially closed. Keep adjusting until the rooms are balanced. No vents should be completely closed.

This can help improve the balance but may not always work. In some cases ductwork needs to be rerouted for better balance.

Here is the full list off all the causes of central AC problems:

*dirty air filter
*dirty condenser coils
*evaporator coil frozen due to blocked airflow – dirty filter
*thermostat malfunction (not switched on, not calibrated, incorrect programming, failure)
*leaky ducts
*low refrigerant/refrigerant leak
*blocked condensate drain
*components not plugged in or switched on/safety switch off
*capacitor failure
*transformer failure
*relay failure
*control board failure
*corroded, burned or loose wiring
*worn electrical contactor
*tripped breaker
*worn breaker
*blown fuse (circuit board)
*safety disconnect not fully inserted
*compressor failure
*fan motor failure, worn bearings
*fan motor dirty or not lubricated
*fan control board failure
*worn, broken blower belt

If your central AC problems are beyond your ability to fix it yourself, give us a call within the New York City Metro area 718-690-3718.

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