How To Perform Typical Air Conditioner Troubleshooting

Air conditioner troubleshooting

In this post, we will discuss how to perform typical Air Conditioner troubleshooting procedures to save you time and money.

When an air conditioner goes out a homeowner may not know if it’s a big or small issue. The only way you will be able to determine the problem is by troubleshooting the ac system.

Here are some of the common issues you may need to troubleshoot.

Airflow Restriction.

If you need to do air conditioner troubleshooting then I would start out by checking your airflow. The airflow plays a major role in the overall operation of the whole system. In the picture below you can see the evaporator coil is restricted by impacted dust and other biological growth. The other issue with airflow is when the blower motor stops spinning as fast as it should. This will throw all of the other important aspects of the air conditioning system off.

air conditioner troubleshooting dirty evaporator coils
ac troubleshooting dirty evaporator coils

I have also seen where one of the main return or supply ducts or trunk lines is collapsed in on itself and preventing airflow. If this is the case you will need to visually inspect the duct system to determine if it’s collapsed. If the return air or air flowing into the air conditioner system is collapsed then the heat from the property can’t get to the evaporator coil to be conditioned. If the duct is collapsed on the supply side of the airflow ducts then the air can make it into the system but can’t make it out at an adequate flow. Air filters are also something to troubleshoot. make sure you check all of the filters connected to the system. Some of the filters are in the


If the refrigerant (FREON) is low your system may still be coming on but not cooling the home very well. Some systems have R-22 refrigerant and others use R-410A refrigerant. The refrigerant is the vehicle that absorbs the heat in your home and carries it out. If your refrigerant is low that’s one of the common reasons your air conditioner isn’t working. A refrigerant leak may be anywhere from the condenser outside all the way to the evaporator coil inside. A service technician will use a tool that will beep when refrigerant comes in contact with the probe. Typically when an HVAC system is still working and the copper line outside is freezing up that may be an indication the system is low on refrigerant.

If the refrigerant is low and a section of the copper line is freezing this is a good indication of low refrigerant. When the refrigerant is not low enough to cut off the system on low pressure but still has enough in it to run it will freeze up. On service calls, I run into this situation all the time. Keep in mind just because the copper line, compressor, or evaporator coil is freezing up its not always low refrigerant. Having a really dirty evaporator coil or a really dirty air filter will cause similar things to happen.

Bad Fuse.

Your air conditioner has fuses on the outside system and on the inside system. On the outside condenser, the fuses are typically located at the disconnect box. The disconnect box can be on the wall of the house close to the condenser. The picture below shows the gray disconnect box. Some of them have a pull-out that contains cartridge fuses.

air conditioner troubleshooting
Troubleshooting a bad ac fuse.
Troubleshooting a bad ac fuse

The system also has fuses on the inside air handler or furnace. The inside may have both high and low voltage fuses. The high voltage cartridge fuses will sometimes be in the same type of disconnect you saw in the picture up top. You test the fuses using a multi-meter that can be purchased from Walmart or home depot. It’s not required to get the most expensive meter to test the fuses or just about any other part of your system. A cheap multi-meter from Walmart for under $15 dollars and test almost anything to need to troubleshoot your ac system.

The low voltage fuse is normally located somewhere on the circuit board.

Reasons Why An Air Conditioner Compressor Isn't Running
Notice the 3 amp purple fuse on the circuit board

The fuse is installed as a safety device to protect your system and shut off power if an unsafe condition occurs. The low voltage fuse protects the circuit board from getting damaged in case the thermostat wires get damaged at the condenser. Or if the low voltage wires get damaged anywhere along the whole circuit. If you install another low voltage fuse and it blows right away then you will have to trace out the low voltage wires to determine where the copper is touching and causing the fuse to blow.

Weak Capacitor.

The capacitor may be on the inside and the outside HVAC system. When the capacitor is really weak or bad the motors will not run correctly. The motors may not even start up.

common reason an ac wont come on
Ac troubleshooting a dual-run capacitor

Troubleshooting the air conditioner capacitor on the inside is on the blower motor and assists the blower motor. The other capacitor is on the condenser outside and is used to assist the condenser fan motor and the compressor.

Single run capacitor
Single run capacitor

Some systems have these types of capacitors and some don’t. The advanced systems that are full-variable speed and high efficiency may not have the capacitors like the lower efficiency 14 & 16 seer systems.

common reasons hvac wont come on
Dual Run Capacitor

A single run capacitor will start and operate a single motor such as a condenser fan motor or a blower motor. Air conditioner troubleshooting on a dual-run capacitor will be in the condenser and will assist the condenser fan motor and the compressor motor. If you look at the picture above you can see the top of the capacitor is swollen which indicates it’s bad. Professional HVAC technicians use multimeters to test capacitors. The bottom line is a capacitor is a Common Reason Your Air Conditioner Isn’t Working. The capacitor going bad is a common issue especially if the unit is in an extremely hot environment.

Bad Contactor.

Depending on what type of system you have there may be more than 1 contactor on the HVAC system. You can see from the picture below the contactor is burned and pitted. The metal has basically welded together causing the condenser to stay on 24/7. When you have natural gas as your heat source then you will most likely only have a contactor on the condenser outside.

Common Reasons Your Air Conditioner Isn't Working

Because the contactor isn’t transferring power from one side to the other then the equipment will not receive the proper voltage. It’s not good either way but you definitely don’t want the contactor to stick and stay on. When you look closely at the contactor above you will see the contact tips are burned and damaged. That contactor had to be changed so the condenser would come on. The contactors also have a coil that comes on when low voltage 24V is sent to the coil. The coil can go bad for a multitude of reasons. Sometimes when the contactor sticks and stays on for an extended time period the compressor will overheat and stop running on a thermal overload.

how to troubleshoot a difficult system
Troubleshooting the HVAC contactor

If you have electric heat on the air handler then you may have a bad contactor preventing components from coming on. On the Trane and Carrier advanced high-efficiency systems, an electric air handler has multiple contactors that are difficult to access. Because contactors are (wear and tear) and will typically not last the whole life of the system it’s one of the Common Reasons Your Air Conditioner Isn’t Working and may need to be changed.

Tripped Breaker.

The circuit breaker might be tripped and the unit isn’t turning on. If you have a 240v condenser and a 240v air handler then those will be 2-pole breakers. Your breaker may be tripped or it may have turned off because of a major part going bad. If you try to turn on the ac 2-pole breaker and it shuts off right away this is most likely because a part is grounding out.

air conditioner troubleshooting
2-pole breaker

The 2-pole breaker above will be in the electrical panel box on your home. The breaker will shut off when it senses a component is overheating or has grounded out causing a direct short.

The Most Common Reasons Your Air Conditioner Isn't Working
single pole breaker

If you are doing air conditioner troubleshooting on a 120v furnace or another type of 120v unit then that will be a single-pole breaker. The picture directly above is a single-pole breaker and is what it will look like in your home electrical panel. The breaker is there to protect your home and equipment when something goes wrong and needs to be shut down. The single pole breaker shown in the picture directly above may have the lever in the middle position. Sometimes it’s just a bad breaker that simply needs to be replaced. From my experience in the field most of the time the breaker was good and was simply shutting off because it was doing its job. If you are troubleshooting the breaker and it trips right away that lets you know its more than just the breaker.

Bad Thermostat.

The thermostat may be bad and if this is the case it will be a simple repair. Unfortunately, when I was in the field servicing systems I didn’t find very many bad thermostats were the problem.

One of the easiest ways to test if it’s only the thermostat is to jump out the wires in a thermostat. The thermostat is similar to a switch that controls a room light. When a thermostat is bad it isn’t sending voltage to the correct HVAC component and therefore it won’t start.

air conditioner troubleshooting
Typical residential thermostat

When the faceplate of the thermostat is removed the wires will be exposed. Service professionals will use a conductive wire with a magnet or clip on the end to clip onto the t-stat screws and transfer power from one wire to the other.

Air conditioner troubleshooting on the red wire is normally the wire that carries the 24v low voltage into the t-stat. When a wire is introduced to connect the red wire to the green wire the indoor blower motor will come on.

If the ac system isn’t variable speed then the red, yellow, and green wires can be connected. When those wires have connected to the condenser, the blower motor will come on.

When professionals do this test it lets them know if all the system works then it must just be the thermostat. The bottom line is to perform a test to determine if the thermostat is bad or if some other component is bad.

Bad Blower Motor.

Bad blower motor air conditioner troubleshooting when the blower motor may be bad. When this is the case the condenser outside may come on but the inside blower motor isn’t coming on or circulating air.

One simple way to test if this may be the reason your whole system isn’t cooling or heating is to turn on the fan at the thermostat.

The Most Common Reasons Your Air Conditioner Isn't Working

The thermostat has a switch that says fan on or fan auto. Turn that switch to fan on. If the fan comes on and is blowing as normal then you know it’s working as normal. If the fan motor doesn’t come on then you know it may be the blower motor.

It may also be the circuit board but this is just a simple test to try and isolate where to start the troubleshooting.

Bad Condenser Fan Motor Air Conditioner Troubleshooting.

The condenser fan motor may be bad. This is also a very common reason the system won’t come on. This issue is fairly easy to determine.

Turn the system on and if the inside seems to start normally and is blowing air then go outside and check if the condenser fan is turning.

How To Change A Goodman Air Conditioner Condenser Motor

Assuming the other components are transferring power correctly this may isolate the problem to just being the condenser fan motor.

air conditioner troubleshooting for why the  breaker will trip

The above pictures show what the condenser fan motor and blades look like when they are removed from the units.

Doing this procedure if anything else will assist you in communicating with the service technician about what needs to be repaired.

Bad Thermostat Wire.

In some circumstances, the low voltage thermostat wire is damaged and may have shorted out. I have seen pets damage the low voltage wire by the condenser.

I have seen rodents and squirrels chew through the low voltage thermostat wire. I’ve seen low voltage t-stat wires damaged in attics, under houses, and at the condenser location outside.

How To Perform Typical Air Conditioner Troubleshooting Procedures

If the low voltage wires shorted out it may have blown the fuse on one or more circuit boards. The most common location the fuse would have blown would be on the inside circuit board.

Look at the fuse at the top of this post to see what the fuse looks like. They will normally be a 3 or 5-amp fuse to protect the circuit board.

Bad Ducts.

Having holes in your HVAC system ducts won’t prevent your system from coming on but will definitely hinder the performance. When the system is in the attic and the ducts have a hole the system will suck in hot attic air.

The ducts or plenums may have collapsed or become disconnected. If this is the case the entire system will still come on but without proper airflow. The system will not cool or heat the home without proper airflow.

How To Perform Typical Air Conditioner Troubleshooting Procedures

This duct has a hole in it because another duct became separated.

In conclusion

Some of the most common reasons your air conditioner isn’t working maybe an easy fix. Sometimes the reason a part is bad is due to other more serious problems.

I’m a big believer in having professional routine maintenance on the system.

From my many years working on HVAC systems, it seems like the systems checked by trained eyes are the ones that last the longest without major parts breaking.

This post will help you isolate where the problems may be and allow you to talk to your HVAC professional with more confidence.

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