How to Diagnose and Repair Your Central Air Conditioning

Air Conditioning Diagnostic Quick Reference

Click on the link in the table header to jump to the section of this troubleshooting guide.

Safety Precautions

It's important to prioritize safety when you're troubleshooting an HVAC system. AC systems operate with high voltage and can pose risks of electric shocks, burns, and other hazards if not approached with care. Here are some safety precautions to consider while troubleshooting your AC system.

1. Before beginning any troubleshooting work on your AC system, make sure to turn off the power. You can do this by switching off the main breaker box.
2. Safety glasses, gloves, and long-sleeved shirts can help prevent injuries from sharp edges or burns from hot surfaces. A respirator mask is also recommended in case you're around harmful substances or dust.
3. A voltage tester is a crucial tool for anyone working on an AC system. It helps you determine if a wire or component is live or not, reducing the risk of electrocution.
4. Keep the area around the unit clean and free of debris. A cluttered workspace increases the risk of tripping and falling, leading to injuries.
5. Manufacturer's instructions provide important information on how to safely operate the system and troubleshoot any issues, including what parts to use and tools which are needed for the job.

By taking proper safety precautions when troubleshooting your AC system, you'll minimize the risks of accidents and injuries. Remember to turn off the power, wear protective gear, use a voltage tester, keep the area clean, and follow manufacturer instructions. If you're unsure about any aspect of troubleshooting an AC system, call the pros at Dallas Heating and Air Conditioning.

Tools and Equipment

Having the necessary tools can help you identify the problem and potentially fix it on your own. Here's the tools that the average homeowner should have on hand to diagnose and troubleshoot common AC system issues. With the right tools and some basic knowledge, you can save money on repairs and keep your home cool and comfortable all summer long.

• An adjustable wrench for tightening and loosening nuts and bolts that are holding the components of the AC system in place.
• A cordless drill/driver for drilling holes, install screws, and perform other tasks that may be needed when repairing or replacing parts of the AC system.
• An insulated screwdriver to protect you from electrical shocks when working with live wires or components. It's always important to use an insulated screwdriver when working with electrical equipment.
• A multimeter measures voltage, current, resistance, and other electrical parameters and helps you diagnose problems with the electrical components of the AC system.
• Needle-nose pliers to reach and manipulate small components, such as wires and connectors, in tight spaces.
• A nut driver is useful to tighten or loosen nuts that are holding components in place. It can be much easier than using a wrench, especially in tight spaces.
• A socket/ratchet set for tightening and loosening bolts that are holding components of the AC system in place. It can be more efficient than using a wrench, especially in tight spaces.
• A voltage tester is a simple tool that's used to determine whether there is voltage present in a wire or component, and helps to identify electrical problems in the AC system.

If you're not comfortable working with electrical equipment, please contact the pros at Dallas Heating and Air Conditioning to diagnose and repair any issues with your AC system.

Basic Troubleshooting Steps

For each of the components of an AC system, we'll cover:

• What they do.
• Common problems you may see if that part is faulty.
• Common causes of failure.

Power

Central AC systems require a dedicated 240 volt circuit as well as a dedicated 120v circuit capable of handling the load required by the individual parts of the system. The following components require a power supply:

• Thermostat.
• Control board.
• Blower motor.
• Compressor.
• Condenser fan.

Usually it isn't the power that's the cause of the AC not working, rather one of the components of the HVAC system that triggered the circuit breaker to blow. Sometimes - during a severe thunderstorm - power systems may encounter surges which in turn could trigger a circuit breaker. If that's the case, it's a simple task of flipping back on the breaker and letting the AC start back up again.

Airflow

In a central AC system, air flows through the return ducts into the air handler unit, where it passes through the evaporator coil and is cooled by the refrigerant. The cooled air is then forced back into the supply ducts by the blower fan and distributed throughout the space via vents or registers. This continuous cycle of airflow provides a consistent and comfortable indoor temperature.

Problems caused by having airflow issues include:

• Low airflow from air vents. Without proper airflow, your AC system may struggle to cool your home effectively. This can result in uneven temperatures, longer run times, and higher energy bills.
• The AC struggles to reach the desired temperature.
• Some rooms may be warmer than others.
• Premature equipment failure. When airflow is restricted, the AC system has to work harder to move air through the system. This can lead to increased wear and tear on the components, which can cause them to break down sooner than expected.
• Reduced indoor air quality: Inadequate airflow can also result in poor indoor air quality. If the air isn't circulating properly, it can become stale and musty, and may contain more dust and allergens.
• Frozen evaporator coil: If the airflow is restricted, the evaporator coil may not receive enough warm air to keep it from freezing. This can cause the system to shut down and require potentially expensive repairs.

Possible causes:

• Holes in the ductwork allowing cool air to escape into the attic.
• Ductwork is bent too tightly, restricting the air flow to certain rooms or areas of the house.
• The ducts become obstructed by debris or are improperly installed.
• The air filter is dirty, which restricts the air flow, and also makes the unit work a lot harder.
• If the blower motor is faulty, it may not be able to circulate air properly, leading to reduced airflow.

Thermostat

Thermostats regulate the temperature in your home or office by controlling the operation of the air conditioning system. Thermostats detect the ambient temperature of the space, then compares it to the temperature set by the user. When the mode is set to cooling, when the current temperature is above the set point, the thermostat will signal the AC unit to turn on and begin cooling until the desired temperature is reached... at which point the thermostat will signal the HVAC system to turn off. Smart thermostats can be programmed to adjust the temperature at certain times of day or based on occupancy, which can reduce energy usage and realize cost savings.

Problems caused by having a faulty thermostat include:

• Inaccurate temperature readings, making it appear that the space is warmer or cooler than it actually is.
• Short cycling (the system turning on and off frequently) which can cause unnecessary wear and tear on the system, increase energy consumption, and reduce its lifespan.
• The blower fan won't turn on - this is responsible for circulating cool air throughout the space.
• The AC system is constantly running.
• The AC system won't start.

Possible causes:

• The thermostat is old and / or broken. (it's usually cheaper to just replace it)
• The thermostat isn't calibrated properly.
• It's in a location which is exposed to direct sunlight.
• There's a draft that can affect temperature measurement.
• No signal getting to the AC system - perhaps due to a wiring issue between the thermostat and the air conditioner.
• No power getting to the thermostat because the AC circuit breaker has tripped.
• The thermostat isn't sending a signal to the air conditioner to turn off when the desired temperature is reached.

Air Handler

The air handler has three functions:

1. Suck in warm air from your home via the return vents.
2. Blow the warm air across the evaporator coils, which then cools it.
3. Blow the cool air back into your home via the AC vents.

Problems caused by a faulty air handler include:

• Excessive noise from the air handler motor like a humming or buzzing.
• Air flow is reduced or completely stopped.

Possible Solutions:

• Replace broken AC blower belt.
• Diagnose & fix or replace the blower motor.

Condenser

The condenser in an HVAC system plays the role of releasing the heat absorbed by the refrigerant in the evaporator coil to the outdoor air. It takes the hot gas, passes it through a series of coils that are cooled from outside air being blown across the fins on the coil.

Problems caused by having a dirty condenser include:

• Reduced cooling capacity and longer cooling times because it can't release heat as effectively.
• The air conditioning system has to work harder, leading to increased energy consumption and higher energy bills.
• The system pressure can increase, potentially leading to system damage as the condenser struggles to release heat.
• The air conditioning system can draw too much power, which can trip circuit breakers or blow fuses.
• Overheating and possible failure of the compressor if the condenser is clogged for an extended period of time - this is expensive to repair or replace and you'll need a qualified HVAC technician to correct this.
• Extra strain on the air conditioning system, potentially reducing its lifespan and requiring more frequent repairs.
• Warm air blowing from the vents as the system struggles to cool the air.
• Unusual noises or vibrations from the unit as the system works harder to compensate for the clogged condenser.
• Leaks or excessive moisture around the condenser, potentially leading to leaks or other issues.
• The AC struggles to reach the desired temperature.

Possible causes:

• Dust, dirt, leaves, tree pollen, grass clippings and other debris can get sucked into the condenser and clog the fins.
• Insects and small animals can build nests in or around the condenser, blocking airflow and causing damage to the fins.
• Harsh weather conditions such as hail or strong winds blowing objects into the unit can damage or bend the fins, causing them to become misaligned and reducing airflow.
• Normal wear and tear on the air conditioning system can cause the fins to deteriorate and become less effective at releasing heat.
• Failure to clean or maintain the condenser regularly can lead to clogged fins.
• Age and corrosion
• Failure to properly maintain and service the system.

Low Refrigerant

Refrigerant is used in a central AC system as part of a closed loop system consisting of a compressor, condenser, evaporator, and expansion valve. Refrigerant passes through these components and gets converted from a liquid to a gas and back to a liquid, absorbing and releasing heat in the process.

Warm air from inside the home passes over the evaporator coil, the refrigerant absorbs heat from the warm air and evaporates inside the evaporator coil. Now - as a gas - the warm refrigerant is pumped outside to the outdoor unit & condenser coil, where the refrigerant releases the absorbed heat to the outdoor air and condenses back into a liquid.

Refrigerants used in HVAC systems are R-410A and R-22... although R-22 has been phased out in favor of R-410A, since it's more environmentally friendly and also more efficient.

Problems caused by having low refrigerant include:

• The air coming from the vents may not be as cool as it should be, making it difficult to maintain a comfortable indoor temperature.
• Increased energy bills due to the HVAC system having to work harder to maintain the desired temperature.
• Evaporator coils freezes due to low refrigerant levels, leading to reduced airflow and potentially damaging the compressor.
• Short cycling (the system turning on and off more frequently than usual) when the thermostat senses that the desired temperature has not been reached.

Possible causes:

• Refrigerant can leak out of the system due to corrosion, faulty connections, or wear and tear over time.
• If the HVAC system wasn't properly installed, it may not have been charged with the correct amount of refrigerant.
• A dirty or damaged evaporator coil can cause refrigerant to be absorbed into the coil and not circulate properly through the system.

Capacitors

Capacitors are an important component in an HVAC  system as they help to start and run the electric motors that power the system's fans, compressors, and other components. They are typically located near the motors they serve, so for example, in a central air conditioning unit, capacitors may be located near the compressor and blower fan motor.

Problems caused by having a bad or failing capacitor include:

• The system won't start or is slow to start - the capacitor may not be providing enough energy to start the motor.
• The system is running but not producing cold or warm air because a weak or failing capacitor can cause the motor to run inefficiently, leading to reduced cooling or heating output.
• The motor may make strange noises or produce a humming sound.
• The circuit breaker keeps tripping, and shutting down the system.

Possible causes:

• Old and worn out - capacitors can deteriorate over time and lose their ability to hold an electrical charge.
• Power surges caused by lightning strikes or other electrical issues can damage the capacitor.
• If the capacitor is not installed correctly or with the right specifications, it may fail prematurely.
• Accumulated dirt and debris can cause the capacitor to overheat and fail.
• Corrosion on the capacitor's terminals or connections can cause it to malfunction.
• If the capacitor is located in a hot environment or is exposed to high temperatures, it may overheat and fail.

Condensate Drains

The purpose of the drain line in an AC system is to remove the condensate generated by the cooling process in the evaporator coil and air handler unit - preventing it from building up and potentially causing water damage or mold growth. It's taken away from the unit and drained into the house's sewer system or some other kind of drain outside the house.

Problems caused by having a clogged condensate drain line include:

• The AC won't start, or runs for a brief period before shutting down.
• Water backs up and overflows from the drain pan, leading to water leaks and possible damage to the surrounding walls, ceilings & floors.
• Water lays in the drain pan, creating a breeding ground for bacteria and mold, possibly creating an unpleasant smell in the area.

Possible causes:

• Dirt, dust, and other debris can accumulate in the drain line pipe, which causes a blockage that prevents water from draining properly.
• Algae and mold can grow inside a drain line if it's not properly cleaned and maintained - this can lead to a blockage that prevents water from draining
• properly; this can also cause unpleasant odors and reduced indoor air quality.
• Failure to perform regular maintenance, such as checking and cleaning the drain line.
• The drain pan or the drain line may not have been installed at the correct angle, causing water to collect and potentially creating a blockage.
• If installed, a malfunctioning condensate pump may fail to clear out the condensate from the system.

Compressor

The compressor plays a crucial role in the cooling process by compressing the refrigerant into a high-pressure gas, which raises its temperature and prepares it for transfer to the condenser. There are several types of compressors:

• Reciprocating compressors which use pistons to compress refrigerant gas.
• Scroll compressors which use two interlocking scrolls to compress refrigerant gas - they are known for their quiet operation and efficiency.
• Rotary compressors use a rotating shaft with blades to compress refrigerant gas and are commonly used in larger HVAC systems.
• Screw compressors use two rotating screws to compress refrigerant gas and are known for their efficiency and reliability in commercial and industrial applications.

Problems caused by having a failing or failed compressor include:

• Warm air may be blowing from the vents due to reduced refrigerant flow.
• Unusual noises such as grinding, clicking, rattling, or more noisier than normal.
• High energy bills because the HVAC system is using more energy to maintain the desired temperature.
• A tripped circuit breaker because of a failing compressor and a high current draw.

Possible causes include:

• Electrical issues such as a blown fuse, faulty wiring, or a failed capacitor.
• Lack of maintenance such as cleaning, lubrication, and regular inspections can cause a compressor to fail prematurely.
• Issues with the refrigerant such as low levels, incorrect type, or poor quality.
• Overheating caused by poor ventilation, high outdoor temperatures, or a lack of refrigerant flow.
• Age / wear and tear - compressors have a limited lifespan.

Frozen Evaporator Coil

The evaporator in an air conditioning system is responsible for absorbing heat from the indoor air, which cools and dehumidifies the air before it is distributed back into the home.

Problems caused by having a frozen evaporator coil include:

• A frozen evaporator coil will struggle to absorb heat from the air, which can result in reduced cooling capacity. This means that your AC system may not be able to keep your home as cool as you'd like, or may take longer to reach your desired temperature.
• When the evaporator coil freezes over, ice can build up on the coils, restricting the flow of air through the system. This can cause a drop in airflow, reducing the efficiency of the AC system and making it less effective at cooling your home.
• If the evaporator coil continues to freeze over, it can cause the AC system to shut down completely. This is a safety feature designed to prevent damage to the system.
• When your AC system is not running efficiently, it will require more energy to cool your home. This can lead to higher energy bills, even though your home may not be as cool as you'd like.
• Compressor damage: In extreme cases, a frozen evaporator coil can cause damage to the compressor, which can be costly to repair or replace.

Possible causes include:

• If refrigerant levels are low, the evaporator coil may not receive enough refrigerant to work properly... causing the coil to freeze over.
• (possibly a cause to the previous item) refrigerant leaks can cause a drop in refrigerant levels, leading to a lack of refrigerant reaching the evaporator coil, which could cause it to freeze over.
• Dirty or clogged air filters might cause a restriction in airflow, leading to the evaporator coil becoming too cold and freezing over.
• Dirt or debris on the evaporator coils can interfere with heat absorption, which can cause the coils to become too cold and freeze.
• Problems with the ductwork or vents can cause a restriction in airflow - preventing warm air from reaching the evaporator coil and causing it to freeze.
• A bad blower motor can cause the airflow to slow down, which might result in the evaporator coil becoming too cold and freezing.
• Dirty or damaged condenser coils: Dirt, debris, or damage to the condenser coils can interfere with heat dissipation, leading to a drop in refrigerant levels and causing the evaporator coil to freeze over.

Here's the link to the detailed troubleshooting guide for a frozen evaporator.

When to DIY, and When to Call a HVAC Pro

It's important to know if you can tackle an AC repair on your own and when it's time to call in a professional HVAC company. Trying to do the repairs yourself can save you some money, but attempting complex repairs without the proper knowledge or tools might end up costing you way more in the long run, and more headaches!

Simple tasks such as changing air filters or cleaning condenser coils can be done by most homeowners with basic tools and knowledge of their system. However, if your AC unit is making strange noises or not cooling properly, it's best to leave the repairs to a trained HVAC technician.

Attempting to fix electrical issues or refrigerant leaks without proper training and equipment can be dangerous and potentially harmful to both yourself and your home. A professional HVAC technician has specialized training and experience that allows them to quickly diagnose and repair complex issues while ensuring safety protocols are followed.

In addition, if your AC unit is still under warranty, attempting DIY repairs could void the warranty altogether. It's important to read through the manufacturer's warranty before attempting any repairs on your own.

So...knowing when to tackle a repair yourself vs. calling in a professional comes down to assessing your comfort level with the task at hand - if you feel confident in your abilities and have the necessary tools, go ahead and give it a shot!