What is an AC relay switch?

An AC relay switch is a component in your air conditioning system that controls the electrical current to the compressor, enabling it to cool the air effectively.

How can I tell if my AC relay switch is faulty?

Signs of a faulty AC relay switch include weak or intermittent cooling, unusual odors, strange noises, and higher than usual electric bills. In Bozeman, MT, these issues can be particularly concerning during the warmer months.

What should I do if I suspect my AC relay switch is failing?

If you notice signs of a failing AC relay switch, it's important to contact a professional HVAC technician promptly to prevent further damage and ensure your air conditioner operates efficiently, especially during the hot summer days in Bozeman, MT.

Detecting a Faulty AC Relay Switch: 5 Signs to Watch For

Premier Systems

March 10, 2023

One of the most common air conditioning repairs technicians make in the summer months is replacing a faulty AC relay switch. Like many components in electronic devices, parts inside air conditioners can wear out and malfunction over time. Unfortunately, many of these malfunctions occur on the warmest summer days, leaving you and your family feeling overheated and uncomfortable.

Staying alert to the signs of a failing relay switch helps ensure you schedule professional repairs before a broken part stops the air conditioning from working altogether. Sometimes, even a seemingly minor noise or slight change can signal major trouble brewing. However, ignoring them can lead to expensive and inconvenient repairs.

Premier Systems, the leading AC repairexperts in Bozeman, are ready to help local homeowners keep their air conditioners running all season. Here, we highlight some of the most common signs of a failing relay switch so you know when to call us for help. If you notice any of the following issues, call us at (406) 351-6585 to schedule repairs.

What Is a Relay Switch in an Air Conditioner?

Every electrical system uses a series of switches to help control the electric current. When a switch works correctly, electric current flows between two terminals without interruption. A faulty switch prevents the current from flowing; the switch may be open, but there's no current or power between the terminals.

In an air conditioner, the relay switches send power to the compressor, which is the heart of the system. Without the compressor, the air conditioner would be unable to remove heat from the air inside your home and replace it with cooled air.

The compressor turns refrigerant inside the coils from a cool, low-pressure liquid into a hot, high-pressure gas. This high-temperature gas supports evaporation, which produces the cold air that blows from the air conditioning vents. If the compressor fails for any reason, the air conditioner cannot produce cold air.

The Most Common Signs of a Faulty Relay Switch

In many cases, it's easy to spot a problem with the air conditioner's relay switch. To help you recognize trouble in your home air conditioning system, here are some of the symptoms and signs of a faulty AC relay switch.

1. Weak Cooling

If your air conditioner isn't producing very much cold air, even on the highest setting, the compressor may not be getting enough electrical current to compress the refrigerant. A failing switch doesn't transmit adequate load current from the power source, preventing the compressor from creating the liquid refrigerant that cools the air. Without adequate pressure, the refrigerant will remain a gas and won't flow into the evaporator coils and remove heat from the air.

Eventually, a broken relay switch will prevent the compressor from working at all, resulting in only warm air flowing from the vents.

2. Intermittent Cooling

Another sign of a failing relay switch is intermittent or inconsistent cooling. When the compressor does not receive adequate power, it may work sometimes and not others. Worn contact points inside the part lose their ability to consistently make and break connections, which can result in unreliable cooling.

In addition to age-related wear and tear, dirt and contamination accumulating on the contact points inside the switch can result in contact resistance. This eventually contributes to switch failure and causes intermittent function issues with the air conditioner. If you're holding your breath and hoping that the air conditioner turns on when you need it, it's likely a relay issue.

3. Odors

Sometimes, a faulty switch can cause a smoke or burning smell. A bad relay connection can produce a great deal of heat, and this excess heat can cause the plastic coating on the internal wiring to melt and produce an unpleasant odor. In extreme cases, the excessive heat can even cause a fire inside the air conditioner's outdoor unit.

4. Noise

One surefire sign that the relay switch is faulty is that the compressor does not turn on. Typically, you will hear the compressor turn on when the air conditioner turns on. This is typically a series of clicks as the clutch turns on and engages, followed by the low hum of the blower motor.

If you turn on the air conditioning and do not hear any clicking sounds, the compressor most likely is not receiving any power, so it cannot kick on. If you hear a rattling noise or it seems like the air conditioner is having difficulty starting up, it often means the switch is starting to fail.

5. Higher than Usual Electric Bills

Because the air conditioner has to work much harder to start up and produce cold air when the relay switch is not working correctly, it uses significantly more power than usual. This can cause a noticeable increase in your power bills. Keep an eye on your bills to catch problems before they drive up costs and ensure energy-efficient cooling.

Diagnosing a Faulty Switch

HVAC technicians can check for faulty relay switches using a multimeter or voltmeter. A multimeter can determine whether the electric current flows consistently between two terminals. A voltmeter checks the voltage in each terminal, ensuring both sides of the relay have the same voltage and neither side has low power or exceeds the voltage rating.

If tests show that the current isn't consistent or the voltage isn't correct, replacing the relay switch may solve the problem. If it doesn't, the issue is elsewhere in the air conditioner. In either case, for safety reasons, repairing and replacing the electrical components of an air conditioner is a job best left to the professionals.

Air Conditioning Repair Services from Premier Systems

Premier Systems understands that staying cool during the Montana summer is a priority. We are here with a full array of air conditioning installation, repair, and maintenance services to help you do just that. As the leading heating and cooling provider in the area, our licensed and educated technicians have the experience you can trust to preserve indoor comfort all year round.

When you call us for help getting your air conditioner working again, we'll perform a full inspection and evaluation. Once we determine the issue, we review information with you about the repair options and costs and help you find a solution that keeps you cool and fits within your budget. We carry most parts and supplies in our fully-stocked service vehicles, so most customers do not need to wait for parts to come in before they have a working air conditioner.

If we determine that replacing your air conditioner is a better option, we will walk you through the process and help you choose a reliable and energy-efficient option and provide professional AC installation. Ask about Premier Club membership, our money-saving maintenance program, to keep your home's HVAC system in top working condition. Club members enjoy annual HVAC maintenance service, which helps ensure your system operates at peak efficiency every season.

Make an Appointment for Air Conditioning Repair Today

Don't let a failing relay cause an air conditioning malfunction that leaves your family uncomfortable or puts the system in danger of total failure. If your home's air conditioning is not working as expected, and you suspect that the problem is a faulty AC relay switch, contact Premier Systems for prompt and efficient repairs. Our technicians can quickly identify the source of the problem and make repairs to restore indoor comfort.

Make an appointment by calling our Bozeman, MT, office at (406) 351-6585.

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How to Keep Your Indoor Air Clean When Wildfire Smoke Is in the Air

April 28, 2026

Wildfire season has become an increasingly common part of life in Southwest Montana, especially for homeowners in Bozeman, Belgrade, and Four Corners. While the smoky haze outside is easy to see, what’s happening inside your home is often less obvious. Many people assume that simply closing windows and doors will keep them safe—but wildfire smoke can still enter your home and impact your indoor air quality (IAQ) in ways that affect both comfort and health. Why Wildfire Smoke Indoors Is a Serious IAQ Concern Wildfire smoke is made up of extremely fine particles called PM2.5, which are small enough to pass through tiny openings and even some standard HVAC filters. Once inside your home, these particles can circulate through your ductwork and linger in the air. For homeowners in our area, poor indoor air quality during wildfire season can lead to: Coughing, sneezing, and throat irritation Headaches and fatigue Aggravated asthma or allergies Increased strain on your HVAC system Without proper filtration and system maintenance, your home’s air may not be as clean as you think. How Smoke Affects Your HVAC System Your HVAC system plays a major role in managing your indoor air quality —especially during wildfire events. When smoke enters your home, your system can either help remove harmful particles or unintentionally spread them throughout your space. If your system isn’t equipped with the right components, you may experience: Reduced filtration of fine smoke particles Dirty ductwork circulating contaminants Increased wear and tear on system components Decreased efficiency and airflow This is why homeowners across Bozeman and Belgrade are upgrading their systems to better handle wildfire smoke conditions. HVAC Solutions to Improve Indoor Air Quality During Wildfire Season The most effective way to protect your home’s air is through professional HVAC solutions designed specifically for indoor air quality in Four Corners, Belgrade, and Bozeman. Upgrade to HEPA or High-Efficiency Filters Standard filters aren’t designed to capture the smallest smoke particles. Upgrading to HEPA filters or high-MERV rated filters allows your system to trap significantly more airborne contaminants, improving your IAQ immediately. Install Whole-Home Air Purification Systems Advanced air purification systems integrate directly into your HVAC system to continuously clean the air as it circulates. These systems are especially effective during wildfire season when outdoor air quality is poor for extended periods. Add an Air Scrubber Air scrubbers go beyond traditional filtration by actively removing pollutants, odors, and particles from the air and surfaces in your home. This added layer of protection can make a noticeable difference in homes affected by wildfire smoke. Schedule Professional Duct Cleaning If smoke has entered your home, particles can settle inside your ductwork. Duct cleaning removes built-up contaminants and prevents them from being recirculated, helping restore cleaner air throughout your home. Keep Up with HVAC Tune-Ups Regular HVAC tune-ups ensure your system is running efficiently and filtering air properly. During wildfire season, a well-maintained system is critical for maintaining healthy indoor air quality. Long-Term Protection for Homes in Bozeman, Belgrade & Four Corners Wildfire smoke isn’t just a temporary inconvenience—it’s an ongoing challenge for homeowners in Southwest Montana. Investing in indoor air quality solutions through your HVAC system provides long-term protection for your home and your family. By combining: High-efficiency filtration Whole-home air purification Air scrubbers Clean ductwork Routine system maintenance …you can significantly reduce the impact of wildfire smoke indoors. Breathe Easier with the Right HVAC Support Your home should be a place where you can escape poor outdoor air—not bring it inside. With the right HVAC upgrades and maintenance, you can take control of your indoor air quality in Bozeman, Belgrade, and Four Corners, even during the peak of wildfire season. If you’re noticing smoke lingering in your home or want to prepare ahead of time, working with a trusted HVAC professional can help you choose the best solutions for cleaner, healthier air. Cleaner indoor air starts with the right system—and the right team behind it.