Air conditioner (AC) compressors will stop working because of a faulty fan, insufficient lubrication, blocked suction lines or insufficient/excess refrigerant. Electrical problems, dirty filters or a broken thermostat can also prevent an AC compressor from functioning.
Almost 250 million households across America use some form of air conditioning. However, a dysfunctional compressor can stop the AC from cooling our homes.
There are a few different problems that cause a faulty AC compressor, and each one has its own symptoms to help you figure out which specific problem your AC has. This troubleshooting guide walks you through how to fix each of these problems.
What The Compressor Should Do In An AC
The compressor works in together with the refrigerant to cool our homes.
After the rotating fan draws in hot and moist air, it’s absorbed by the refrigerant. The evaporator coil then converts the refrigerant into a low-pressure gas.
For the room to cool down, the AC expels the hot air out of the house, but to do so, its temperature needs to be higher than that outside.
This is where the compressor comes into play.
It compresses the refrigerant, raising its pressure and consequently increasing its temperature. This high-pressure gas then flows through the condenser, where it converts back into a liquid form, and in the process, it removes the heat.
How to Know Your AC Compressor Is Failing
Here are the signs to look out for in a faulty AC compressor:
- Warm air is blowing out of the vent
- Circuit breaker trips often
- Outside compressor unit buzzes or clicks when starting
- The outside compressor unit is covered with frost
- The compressor light doesn’t turn on
- Overheating
- Reduced or no cooling in the room
Reasons Why Your AC Compressor Isn’t Working
Here are all the causes you should look for if your AC compressor stops working. It’s easiest to work through these one at a time until you find which specific problem your compressor is suffering from – then hopefully it’s one with an easy fix!
1. Dirty Filter
When the fan draws air inside the AC, it passes through a filter that traps most of the contaminants in it. This ensures that dust and debris from the air don’t damage the AC components.
Naturally, over time, the filter becomes clogged. This makes the filter incapable of sanitizing the air, and the whole unit can become contaminated. As a result, the entire system, particularly the compressor (because it regulates the flow of refrigerant), is placed under stress, eventually ending in serious damage.
If the compressor isn’t working and the system is overheating, a dirty filter is likely the cause of the problem.
Fix
- Clean or replace the AC filter:
- Turn the AC off and use a screwdriver to remove the front panel.
- The filter is located in front of the panel.
- Take the filter out and use a handheld vacuum to remove dust and other pollutants from the filter.
- If the filter is more than 45 days old, ask your AC service provider to install a new HEPA filter in place of the old one.
As a preventive measure, always change AC filters regularly, i.e., in 45 days (or sooner depending on the pollution).
Plentiful Air has more information on what causes yellow AC filters and how to fix them available here.
2. Broken Thermostat
AC units have a thermostat that measures the room temperature and displays it on the screen.
The AC shuts off the cooling cycle for some time when the set temperature is reached, and this is when the compressor and other parts of the appliance stop working.
If the thermostat breaks or its sensor starts malfunctioning, it registers the wrong temperature reading.
As a result, the AC resumes the cooling cycle prematurely, which sends the compressor into overdrive. If the problem is not addressed immediately, overheating can cause permanent damage to the compressor.
A broken thermostat is evident if the thermostat and/or AC is non-responsive to adjustment in temperature or the display screen is blurry or incomplete.
Fix
- Reset the circuit breaker for the AC unit and then turn the thermostat on after 30 seconds to see if it resumes functioning.
- If restarting the thermostat does not help, you will need to call in an AC/HVAC expert and have the thermostat replaced.
3. Electrical Problems
Electrical problems are one the most common causes of compressor failure. A power surge from the connected source can lead to a build-up of acid in the compressor.
As a result, the temperature of the discharge area of the compressor increases abnormally. This then leads to compressor burnout.
If you notice a pungent smell coming from the compressor unit or fan, or coils and other components have all started acting up simultaneously, inorganic acids in the compressor are likely the cause.
Fix
You can rely on the filter-drier to remove this acid. AC/HVAC units have pre-installed filter-driers that can efficiently remove acid present in refrigerants and on hard surfaces.
The problem happens when some inorganic substances from the hard surfaces doesn’t reach the filter-drier.
So if the pungent smell from the compressor unit persists, consult a technician. They usually use anti-acid additives to tackle the issue. The compressor is inspected for burn-out and is also replaced if needed.
Keeping the moisture in the room in control and getting the system serviced with lubricants, plus having enough anti-oxidant and anti-corrosive substances is the key to preventing acid build-ups.
4. Leaking Refrigerant
The compressor pushes the refrigerant through the system. Therefore, when the refrigerant levels in the unit are insufficient, the compressor applies extra pressure to regulate its flow.
This causes the compressor to overheat, which, if left as is, can end up in permanent damage.
When short of refrigerant, the unit starts to freeze, and the frost is visible on the valves outside.
AC does not use up the refrigerant, so if the refrigerant in the appliance is insufficient, it is likely happening due to a leak.
Corrosion in coils, as well as acid build-up, causes cracks in the coils or body of the unit, which allows the refrigerant to escape.
Fix
Home AC units have sealed refrigerants and it is not possible for you to recharge the appliance yourself. Call an AC expert to top off the refrigerant as well as seal any leaking points.
To prevent further leakage, the AC technician will locate the cracks and use aluminum flux weld to fill them up. Since corrosion in coils is one of the primary causes of refrigerant leaks, regular AC/HVAC maintenance can prevent the problem from occurring altogether.
5. Excess Refrigerant Flow
Excess refrigerant causes subcooling in the unit and can also directly damage the mechanical parts of the compressor. Since high levels of refrigerant cause an increase in pressure, it puts stress on the entire unit, especially the compressor, and can lead to it malfunctioning.
If your AC compressor starts showing problems after a recharge or re-gassing, the probable problem is high levels of refrigerant.
Fix
A machine called a reclaimer is used to recover extra refrigerant from the HVAC and AC units.
To steer clear of the issue, it is always better to get an AC expert to recharge the appliance.
6. Damaged Condenser Fan
Just like the rotating fan that draws air inside the AC, its outer unit also has a condenser fan that exhausts warm air outside the house.
If the condenser fan stops working for any reason, it allows hot air to stay inside the system. This overheats the compressor and thus, damages it.
You can diagnose damage in the condenser fan if it doesn’t start or if it rotates slower than normal and rattles or buzzes.
Fix
This may be a consequence of an expired or damaged condenser fan motor, an impaired capacitor, or overheating due to a power surge or long operation.
Irrespective of the underlying cause, if the condenser fan is damaged, it cannot be repaired, and you will need to replace it.
Since it is also important to fix the root cause, we recommend getting an AC/HVAC technician to help with a damaged condenser fan.
7. Obstruction In Suction Line
A suction line in the AC carries the gaseous refrigerant to the compressor. If the line becomes blocked because of poor filtration, it won’t pump the gas to the compressor, and the compressor will attempt to use extra pressure to circulate the refrigerant.
This extra load on the compressor eventually damages it.
A rapid decrease in the cooling capacity of the AC is one of the first signs of an obstruction in the suction line.
Fix
You can usually fix the problem by simply using a vacuum:
- Turn the AC off
- Attach the vacuum to the end of the AC drain line and the vacuum suction should remove the blockage in no time.
8. Incorrectly Sized Suction Wire
Suction wire comes in various sizes to match AC units of different cooling capacities.
If the size of your suction wire is too short or long in relation to the size of the AC, it increases the unit pressure, eventually causing the compressor to overheat.
This happens if, during servicing, an inexperienced technician replaces the original suction wire with one of inadequate size. If your AC overheats abnormally after a recent HVAC service, the size of the suction wire is possibly the reason.
Fix
You will need to contact a reliable and experienced technician to replace the suction wire with a new one of appropriate size.
9. Dirty Condenser Coil
Much like other dirty components, a dirty condenser coil also stops the compressor from working properly.
The dirt prevents efficient exhaust, and heat remains in the system. This results in a high compression ratio which ends up damaging the compressor in the long run.
If your AC overheats a short time after turning it on or takes a lot of time to cool the room down, it is a sign of an impaired or damaged compressor.
Fix
If the coils are blocked or dirty, cleaning them will help resolve the problem. Here’s how you can do it:
- Turn the AC off and then refer to your AC/HVAC manual to open the appliance
- Use a dry cloth to remove dust off the coils
- Now prepare a detergent solution in warm water
- Locate the condenser coil and spray the solution all over it
- Let the detergent settle for a while to loosen the debris and then use a cloth to wipe the coil
- Ensure that the coil is completely dry before reassembling the AC
Frequent cleaning as part of regular maintenance helps prevent the issue and prolongs the optimal lifespan of the entire unit.
10. Insufficient Lubrication
Oil is the equivalent of nutrition for a AC or HVAC unit, and without proper lubrication, the unit will not work properly.
There is a range of oils that provide sufficient lubrication to keep the system in good shape.
A lack of lubrication causes friction between mechanical components of the compressor, which results in damage. If you notice black smoke, rattling, or abnormal odor from the system, it is likely that your AC needs oiling.
Fix
Call in a service provider to oil the AC parts. Don’t forget to get the appliance inspected for possible damage secondary to the lack of lubrication.
How to reset an AC Compressor
To reset the AC compressor, remove the AC from the power supply and flick the breaker on the circuit breaker panel. Locate the reset button, and press and hold it for 5 seconds. Release the reset button and reconnect the AC to the power source. The compressor should resume working 30 minutes after the process.
Certain technical issues can be resolved with just one reset. Particularly, in case of tripping of circuit breaker causing damage to the AC compressor, you may need to reset the compressor to get it back into working order.
Resetting an AC compressor is straightforward. The reset button is present on almost every model, and you can refer to your user manual to help locate the button.
Remember to unplug the AC beforehand to avoid any possible power surge during the process. Open the circuit panel and flip the breaker down. Afterward, hold the reset button down for a few seconds and release. To prevent overload and overheating, compressors take around 30 minutes to start.
What To Do When Your AC Compressor Won’t Engage
It is not safe to operate an air conditioner (AC) if the compressor won’t engage. Operating an AC with a malfunctioning compressor leads to overheating in the AC unit and further damage to the compressor.
The compressor is an important part of the internal circuitry of AC as it compresses the refrigerant and allows exhaustion of hot air outside the house. If you run the AC with a malfunctioning compressor, it won’t cool the room down. Instead, the system will just consume electricity, adding to your bill.
Even worse, the AC will overheat, and you may end up with a permanently damaged system.
If you suspect a broken or damaged AC compressor, turn the appliance off and don’t reconnect it until the problem is fixed.
How to Manually Engage an AC Compressor Clutch
To engage the AC compressor’s clutch manually, disconnect the compressor’s single wire and attach it to the jumper wire. Then, connect the jumper wire to a battery, and this will jumpstart the clutch.
AC comes with a clutch located at the front of the compressor. It rotates while the AC operates and provides energy to the compressor. Many factors like low pressure, a blown fuse, or bad clutch oil can hamper the engagement of the clutch.
In that case, you can jumpstart the clutch manually.
And remember to stick to the maintenance guide in your owner’s manual and always hire only a well-trained HVAC technician to service your AC.