The 24 Most Common Air Conditioning Problems

Mar 2, 2023Air Conditioning, Blog

In the middle of a sweltering Northern California summer, the last thing you want is a malfunctioning air conditioning system. If you are trying to diagnose an issue with your AC unit, you’re in the right place! We put together this article specifically to help you figure out whether your air conditioning problem can be fixed easily, or whether it’s time to call a reputable HVAC company.

Here are the most common issues we see with air conditioning repair here in the San Jose area.

1. AC Does Not Turn On

When the temperature is getting hotter, there’s nothing quite as frustrating as your air conditioner refusing to turn on. Even when you turn the thermostat down to a lower temperature, the cool air still won’t turn on.

If you’re lucky, the cause is simply a tripped circuit breaker or a blown fuse. If resetting the circuit breaker and replacing the fuse doesn’t solve the problem, it could be a faulty thermostat, try replacing the batteries.

In the case these solutions don’t cause your AC system to turn on, the problem can be a faulty thermostat the needs to be replaced, loose wiring in the system, frozen evaporator coils, a clogged condensate drain line, or the AC blower may be damaged due to a faulty capacitor.

When the simple fixes fail to solve the problem, it may be time to call a local HVAC expert.

2. Air Conditioner Won’t Stop Running

A problem on the other side of the spectrum is when your air conditioning won’t turn off, even when your house is freezing cold inside. This is an issue because it can make your energy bills skyrocket. Beyond that, if the problem isn’t fixed, it may cause further damage to your central air conditioning system.

One simple fix to look at: check to make sure your thermostat isn’t set to “Fan”. This setting runs the blower motor and the fan continuously, instead of running the cooling only when the temperature exceeds a threshold.

The cooling cycle should run a few times per hour, for about 15 to 20 minutes, only when it is warmer than the thermostat setting. It will wear out your HVAC unit to run it continuously 24 hours a day.

What are some more technical reasons your AC may not be shutting off?

Bad relay switch. When the relay switch is stuck, electricity keeps running to the air conditioner. The compressor contactor can fuse in a closed position, meaning the condenser unit will run continually. This is a job that will require a HVAC technician to fix.

Faulty fan limit switch. If the fan limit switch is stuck in the override position, the fan motor will keep running, even if the air conditioner isn’t cycling. A HVAC technician can reset the limit switch to stop the fam from blowing unless the colling cycle is running.

3. Air Conditioner Stops Running Suddenly

If you notice that your air conditioner is shutting off randomly every ten to fifteen minutes, this is a phenomenon known as short cycling. Air conditioning units are short cycling when they turn on and off before they cool the environment to a desired temperature. Some of the issues that short cycling causes include higher electricity bills, high humidity indoors, and increased wear and tear on the HVAC system.

Some of the reasons short cycling occurs include defective parts, dirty evaporator coils, a poorly maintained HVAC system, faulty thermostats, frozen evaporator coils, refrigerant leaks, electrical problems, or a capacitor failure.

If your air conditioner shuts off prematurely, be sure to contact a HVAC company to fix the issue before your AC system is damaged further.

4. AC Blowing Hot Air

Imagine it’s the middle of summer, and your air conditioner is blowing warm air. The first thing to check is your thermostat settings. Make sure it hasn’t accidentally been set to “Heat”.

If the thermostat looks correct, the most likely culprit is frozen evaporator coils. When evaporator coils become dirty due to old, dust-filled air filters, they can freeze, meaning they will not absorb heat from inside your home. It’s a good idea to change air filters every few months. This will help prevent frozen coils.

Another reason your AC system may be blowing warm air is an obstruction in the air ducts and ductwork. Be sure to schedule an air duct cleaning once a year. It may also be possible there is leak in your ductwork.

One more reason your air conditioner might be blowing warm air is a refrigerant leak. The refrigerant absorbs thermal heat, and is a crucial part of both the heating and cooling cycles in heat pump systems and ductless HVAC systems.

You can test whether your refrigerant line has a leak by feeling the larger of the two copper lines running into the AC system’s condenser. If the copper line is cold and moist, your refrigerant levels are good. If the line is air temperature, or does not feel moist, your refrigerant is low, due to a leak in the line. A professional HVAC company can fix the line and replace any lost refrigerant.

5. No Cool Air Flowing

What if you hear the AC running, but no air is coming through the vent? Or if there is some air circulating, but it doesn’t feel cool? There are a few reasons this may be happening.

The first thing you should check is for a tripped circuit breaker. The blower fan may not be running, even if the cooling cycle is running.

It’s also possible the fan blower belt is broken. A refrigerant leak may also prevent the cooling cycle from blowing cold air. If you’re unsure of what is causing the issue, call a reputable HVAC company.

6. Refrigerant Leak

When the coolant starts leaking in the air conditioner, the unit will not perform correctly, and the temperature will fluctuate. The location of the leak will affect the cost of the repair so having this examined yearly by a trained AC technician is advised.

When refrigerant begins to leak in the air conditioning system, it can cause the system to underperform and work harder, causing excessive wear and tear. Refrigerant leaks are often difficult to detect because they are usually slow leaks, in the coolant lines. The refrigerant helps remove heat from the home, and pump cool air back into the building.

Some signs that you may have a refrigerant leak are excessive moisture around the outside condenser/compressor unit, or if the large copper line running to the condenser is warm to the touch.

A professional HVAC technician can determine whether the leak is in the refrigerant line, evaporator coils, or another part of the HVAC system.

7. Drainage Problems – Clogged Condensate Line

As your home is being cooled during the air conditioning cycle, it is also de-humidified. Removing the humidity helps the house feel cooler. That moisture is condensed, landing in the drip pan in the indoor air handler. This water is removed via the condensate drain line, which moves the moisture outdoors.

If you see water dripping indoors, or if you do not see water draining outside, there could be an issue with the drainage.

The drain line may be clogged with dirt, dust, lint, or small amounts of algae. When this occurs, the condensed water vapor does not drain, but backs up into the drip pan. If the drip pan is cracked or damaged, there can also be drainage problems. Water can leak out and damage the AC unit if this is not fixed.

A service call with a professionally trained HVAC technician can get this problem fixed quickly.

8. AC System Freezing Over

If you inspect the evaporator coil or copper lines, and there is ice forming on these, it means your HVAC system is working too hard to keep your home cool. This can cause high energy bills, and if left unaddressed, may cause more damage to your HVAC system.

There may be obstructions around the blower fan, air ducts, or condenser causing the unit to work harder than it has to.

9. Breaker Trips, Fuses Blow When AC Runs

If the circuit breaker constantly trips when the air runs, or if fuses blow on a regular basis, this means there is likely an electrical problem with your HVAC system. If the circuit breaker or wiring is not rated for the output of the HVAC unit, it can cause an electrical overload.

10. Blower Motor Failing

The blower motor in your central air conditioner system moves cooled or heated  air through the vents in your home. The air that is heated by your furnace or cooled by your AC unit moves through your home until each room reaches its desired temperature. Most modern AC systems use direct drive blower motors. There are also two speeds, single speed, and variable speed blower motors. Variable speed motors can blow at a lower speed when the temperature adjustment required is lower.

Some common reasons for blower motor failure are overheating, excessive wear and tear, and excessive moisture. When dust, dirt, and debris build up, it can cause the windings and bearings to burn up more quickly.

Signs that your blower motor is failing are: poor airflow from air vents, no airflow whatsoever, burning electrical smell when you turn on the air, higher than normal energy bills, and strange noises (rattling, squealing) when you turn on the AC.

If you hear or smell abnormal things when the AC kicks on, you may need a new blower motor. An experienced HVAC company can help you solve that problem.

11. Lack of AC Maintenance / Dirty Filters

When you don’t regularly change the air filters on your HVAC system, it can become dirty and clogged, and subsequently overheat. Evaporator coils can get dirty and freeze over, causing the cooling cycle to run inefficiently. Your AC system will work harder to cool or heat your home, causing your energy bills to rise. It is easiest to do regular preventative maintenance and replace the air filters in your home’s HVAC system at least every few months.

12. Bad or Strange Odors Come From AC When it Runs

Strange and abnormal smells coming from your AC system may indicate bigger problems. If you smell electrical or burning smells in the middle of the summer season, this might mean you rair filters are clogged, and your system is overheating.

Mildew or mold smells may indicate you have leaky or damaged ductwork, and condensed water vapor is trapped in the walls or ductwork. This is something you should deal with immediately, so mold does not form in your house.

If you smell something like natural gas or a skunk smell, this may indicate Methyl Mercaptan, a gas line leak, or possibly a sewer line leak. Methyl Mercaptan is a dangerous gas, so take this sign seriously.

13. AC Blows Loudly – Strange Noises

Squealing, rattling, screeching, or banging sounds should not occur when the air conditioning is running. Grinding noises or strange vibrations when the air conditioning or heating cycle starts means there is a problem somewhere. This can be the blower motor, the compressor motor, the motor bearings, a failing belt, or some issue with the air handling part of your AC system. Higher than average energy bills can also be a sign something is wrong.

Be sure to call a qualified HVAC contractor to take a look and fix any problems before they get worse.

14. Thermostat Malfunctioning

The thermostat controls the cooling and heating cycles of your central air conditioning system. If the thermostat is broken or malfunctioning, it can cause several of HVAC issues.

If you suspect the thermostat is malfunctioning, check the batteries to make sure they are fresh and fully charged. Your thermostat should also be in a room where it is not hit with direct sunlight. This positioning can often create recurring calibration issues.

Modern thermostats can be difficult to program initially but are more reliable once they are calibrated. Consult your owner’s manual to ensure your thermostat is properly programmed. Dial thermostats can suffer from calibration issues, especially after many years of use.

If you are experiencing short cycling (the air turns on and off quickly) or if your home is warmer than it should be, you may need to replace your current thermostat with a new one.

15. Uneven Temperature Distribution

Some rooms in your home may seem warmer or cooler than others. This can be caused by the way the ductwork is laid out in ducted systems, With ductless HVAC systems, the air handlers can be set strategically in different rooms to more evenly distribute the cool air.

What you can do to balance out the uneven cooling and heating is make sure that rooms with large windows that face the sun during the day have blinds or curtains, that can reduce the amount of thermal heat that enters the room.

16. Bad Capacitors

If the AC is running, but there is no cold air blowing, it might be a bad capacitor in your condenser/compressor unit.

Capacitors help the electric motors that are in your air-conditioning system start and run. Specifically, they provide a boost of energy during the starting phase to get the motors up to speed. Over time capacitors weaken and eventually if they are not replaced they will “blow” which renders them useless and can sometimes cause other issues inside the unit.

Capacitors help the motors in your AC system start and run, providing an energy boost during the motor starting phase, helping them get up to speed. These capacitors cycle on and off several times per second when the compressor is running. The capacitors are also directly related to the life expectancy of the compressor. The older the capacitors, the shorter the expected lifespan of the compressor.

The capacitors must be replaced at regular intervals with new capacitors with the same rating as the HVAC system, so it matches the air conditioning motors.

You can usually tell if your capacitors are bad by checking the outside compressor unit. The fan and compressor should both be running during the warmer months. The compressor makes a deep buzzing sound; the fan makes a whirring sound. If you hear the buzzing of the compressor, but don’t hear the whirring of the fan motor, or if you don’t feel the fan blowing warm air outside, it is likely you have a bad capacitor.

17. AC Condenser Fan Failure

The condenser fan in the outdoor condenser/compressor unit helps transfer heat from inside your home to the outside and pull cool air from outside. If this fan is broken, the heat transfer will be inefficient, and your home will not cool down properly. A broken condenser fan can also make your electric bill skyrocket.

The fan in the condenser/compressor unit is a critical part of heat exchange within your AC system. It is imperative this fan is functioning correctly.

In extreme cases, if the condenser fan remains broken and unfixed, it can cause damage to the condenser/compressor unit.

18. Condenser Failure

When dirt and debris get into your condenser, this can cause problems for the condenser coils, which are filled with refrigerant. The dirty coils can freeze up, and instead of properly enacting a heat exchange, the coils become much colder than they should be. This can cause the air conditioner to not distribute cold air.

Faulty tubes or leaks in the seals can also cause condenser failure. Some wear and tear can occur after decades of use. If you suspect your condenser is malfunctioning, call an experienced HVAC contractor today.

19. AC Contactor is Worn Out

The contactor is a switch in the outside condenser/compressor unit. It is made up of a metal plunger, a control coil, and one or multiple sets of electrical contacts. This switch turns your AC on and off as needed to maintain the desired temperature.

Over the course of time, with natural wear and tear, the contactor switch can wear out and cause issues with cycling. Even if your air conditioning unit is running perfectly, replacing the contactor every few years as part of a regularly scheduled AC maintenance plan will help prevent future issues, and extend the life of your central air conditioning system.

20. Weak Airflow from AC Unit

If you notice hot drafts or weak airflow from your air conditioning system in the summer, there are a few reasons this might be occurring. Primarily, the fan is not able to push enough hair to cool the home environment. This may be due to a vent blockage, dirty air filters, or a defective blower motor.

21. Outside Debris and Foliage

The outside compressor / condenser unit that sits outside on a cement slab needs to have room around it for proper airflow. Part of the AC maintenance you can do on your own is removing any foliage, brush, branches, shrubs, and leaves from around the unit. This will help it preform at peak capacity and prevent any issues caused by blocking the airflow.

22. Leaky Air Ducts

The ductwork that runs through your walls moves the air from your HVAC system throughout your home. Sometimes this ductwork might be damaged during renovations by accident, or by rodents. There are three big issues with damaged and leaky ductwork. One, condensed moisture can form in the ductwork, and this can leak through holes in the ductwork into the walls, potentially causing hazardous mold. The other issue is that cold air escapes through the leaks in the ductwork, causing inefficiencies in cooling or heating your home. This can cause higher energy bills. Third, dirt and construction materials can also get into the leaky ductwork, and this dirt and dust distributes throughout the system, which can cause buildup on evaporator coils, electrical components, and cause more serious issues.

If you suspect you have damaged ductwork, call a licensed and bonded HVAC contractor to inspect to see if you need air duct or ductwork replacement.

23. Air Conditioning Unit is Oversized or Undersized

Air conditioners come in different sizes and ratings, based on air capacity, measured in “tons”. While it seems logical that an undersized AC system will fail to cool or heat a home appropriately, an oversized system is also inefficient.

A bigger sized HVAC system can run much harder than is necessary to cool a certain area, causing higher energy bills. Oversized AC systems tend to cycle on and off frequently, without sufficiently removing humidity from the air. This extra moisture in the air creates a warmer feeling. Remember the idiom, “It’s not the heat, it’s the humidity.” This same principle also applies in heating and cooling.

Before buying a new heating and cooling system for your home, consult with a professional HVAC contractor to get recommendations, and find the ideal sized AC system for your home.

24. Electric Bill Suddenly Spikes Up

If your electric bills suddenly spike up, it can be an issue related to your HVAC system. A faulty thermostat, malfunctioning sensors, or bad components can all contribute to your AC system working inefficiently and wasting energy.

AC Repair and Installation in San Jose and Morgan Hill

Our professional HVAC team has been helping San Jose residents since 2005. We will provide great service at a reasonable price, making sure that your heating and cooling system works flawlessly.

At Ventwerx HVAC Heating & Air Conditioning, we provide the expertise you need to make sure your home’s temperature is set correctly year-round. To get a no-obligation heating and cooling estimate for your home in San Jose call us at (408) 422-2987, or in Morgan Hill and Gilroy at (408) 710-9595.