At first glance, a 220v mini split wiring diagram can look like a confusing web of lines, letters, and symbols. It’s easy to feel intimidated and question whether you can tackle the job yourself. But think of it like a recipe: once you understand what each symbol means and follow the steps in order, the whole process becomes much clearer. This guide is here to be your translator. We’ll decode the color codes, explain the layout, and show you how to trace the path of power from your breaker panel to your indoor unit, turning that complex schematic into a straightforward, actionable plan for your installation.
Key Takeaways
- Get the Electrical Basics Right from the Start: Your 220v mini split needs its own dedicated circuit, just like an oven or dryer. Using the correct wire gauge and circuit breaker size isn’t just a suggestion—it’s the most important step to prevent overheating and ensure your system runs efficiently without tripping breakers.
- Treat Safety Components as Non-Negotiable: Before you do anything, turn the power off at the main breaker. Installing a disconnect switch near the outdoor unit is required for safe maintenance, and proper grounding is your system’s primary defense against electrical shorts. Skipping these steps puts your equipment and your home at risk.
- Trust Only the Manufacturer’s Wiring Diagram: Generic online guides are helpful, but the diagram on your specific unit is the only one you should follow. Double-check that every wire is connected to the correct terminal and secured tightly to prevent performance issues and future electrical problems.
What Is a 220v Mini Split System?
A 220v mini split is a powerful and highly efficient ductless heating and cooling system. The “220v” simply refers to the 220-volt electrical circuit it runs on—the same type of circuit that powers larger appliances in your home, like an electric stove or clothes dryer. Unlike traditional central air systems that rely on a network of ducts to distribute air, a mini split uses an outdoor compressor connected by a small conduit to one or more indoor air-handling units. This ductless design makes them incredibly flexible.
Because they don’t require bulky ductwork, mini splits are a fantastic solution for home additions, converted garages, or older homes where installing ducts would be too invasive or expensive. They are also powerful enough to provide zoned comfort for your entire home or business. Whether you need a reliable climate solution for your residential living space or a robust system for a commercial setting, a 220v mini split delivers targeted heating and cooling right where you need it most, giving you precise control over the temperature in different areas.
How 220v mini splits work
At its core, a mini split works by moving heat from one place to another. It uses a refrigerant line to connect the outdoor and indoor units. In the summer, the system pulls heat from inside your home and transfers it outside, leaving you with cool, comfortable air. In the winter, it reverses the process, extracting heat from the outside air (yes, even on cold days!) and moving it indoors to warm your space. The 220-volt connection is key because it allows the system to handle a heavier workload more efficiently. It can deliver more power with less electrical current (amperage), making it ideal for heating and cooling larger spaces without straining your electrical system.
Key benefits of 220v systems
Opting for a 220v system comes with some significant advantages that make it a popular choice for both homeowners and businesses.
- Higher Capacity: These systems typically offer a wider range of heating and cooling power, measured in BTUs (British Thermal Units). With capacities often ranging from 9,000 to 36,000 BTUs or more, they can easily handle large, open-concept living areas, workshops, or commercial offices that smaller systems would struggle with.
- Energy Efficiency: Because they operate on a higher voltage, 220v mini splits run more efficiently. They draw less amperage to produce the same amount of power, which reduces energy consumption. Over time, this can lead to noticeable savings on your utility bills.
- Versatility: The power and efficiency of 220v systems make them suitable for nearly any application. They are a perfect fit for demanding residential needs and robust enough for many commercial and industrial HVAC settings, providing reliable comfort in a variety of environments.
Electrical Requirements for a 220v Mini Split
Getting the electrical details right is one of the most important parts of a successful mini-split installation. It’s not just about making the system run; it’s about ensuring it operates safely and efficiently for years to come. Before you or a professional even think about connecting wires, you need to understand the specific power demands of your unit. This includes everything from the voltage and circuit requirements to the exact size of the wires and breakers. Paying close attention to these electrical needs will protect your investment, your home, and your family.
Voltage and amperage needs
Most mini-split systems operate on a 208/240-volt circuit, which is similar to what large appliances like electric dryers or ovens use. While some smaller units (usually under 12,000 BTUs) might use a standard 110-volt outlet, the 220v models are more common for cooling and heating larger spaces. The amperage, or the amount of electrical current the unit draws, typically ranges from 15 to 45 amps. The exact voltage and amperage requirements depend entirely on the size and model of your mini-split, so always check the manufacturer’s specifications first.
Why you need a dedicated circuit
Your mini-split system needs its own dedicated circuit. Think of it as a private electrical lane just for your HVAC unit, with no other appliances or outlets sharing the power. This is a critical safety measure. A dedicated circuit prevents the mini-split from overloading a shared circuit, which could cause the breaker to trip and shut down power to other devices. By isolating the power supply, you ensure your system gets the consistent energy it needs to run efficiently without interfering with the rest of your home’s electrical system. This isn’t just a best practice—it’s a standard requirement for a safe installation.
How to size your circuit breaker
Sizing the circuit breaker correctly is key to protecting your mini-split. A breaker that’s too small will trip constantly, while one that’s too large won’t trip when it should, creating a safety risk. A good rule of thumb is to choose a breaker that is rated for about 25% more than the unit’s maximum amperage draw. For example, if your mini-split has a maximum draw of 20 amps, you’d want a 25-amp breaker. This buffer allows the breaker to handle the initial surge of power when the compressor kicks on without tripping unnecessarily. Proper sizing is essential for both residential and commercial HVAC systems.
Choosing the right wire gauge
The thickness of the electrical wire, known as the wire gauge, is another non-negotiable safety detail. Using a wire that’s too thin for the amperage load can cause it to overheat, melt its protective sheathing, and create a serious fire hazard. Most mini-split installations use a 14/4 stranded conductor cable, but you must confirm the correct gauge in your unit’s installation manual. Because the risks of getting this wrong are so high, selecting and running the proper electrical wire is a job best left to a licensed professional who understands local codes and safety standards.
Essential Components for 220v Mini Split Wiring
Once you understand the wiring diagram, the next step is gathering the right components. Using the correct, high-quality parts is non-negotiable for a safe and reliable installation. Think of these as the essential building blocks that ensure your mini-split system runs efficiently for years to come. Let’s walk through exactly what you’ll need to get the job done right.
Disconnect switch requirements
A disconnect switch is a crucial safety feature. It’s a small, weatherproof box installed near your outdoor unit that allows you to shut off power directly at the condenser for maintenance or emergencies. According to the National Electrical Code, each mini-split system must also have its own dedicated circuit breaker at your main electrical panel. This is vital because it prevents power overloads that could trip other breakers or, worse, create a fire hazard. A dedicated circuit ensures your mini-split has the consistent power it needs without interfering with the rest of your home’s electrical system. For any residential HVAC project, getting this part right is fundamental.
Using an electrical whip and weatherproof protection
The wires running from the disconnect switch to the outdoor unit are exposed to the elements. To keep them safe, you’ll need to run them through a weatherproof casing called an electrical whip. This flexible conduit protects the wiring from rain, snow, UV rays, and physical damage, preventing corrosion and short circuits. Without proper protection, your system’s electrical connections could fail prematurely, leading to costly repairs. Using an electrical whip is a simple but effective step to ensure the longevity and safety of your outdoor wiring, keeping your system running smoothly no matter the weather.
Why you should consider a surge protector
A mini-split is a significant investment in your home’s comfort, and it’s worth protecting. Because the system is always connected to power, it’s vulnerable to sudden electrical surges from lightning strikes or grid fluctuations. A surge protector designed for HVAC systems can absorb these power spikes before they damage the sensitive electronic components inside your unit, like the circuit boards. Installing one is a small, upfront cost that can save you from a much larger repair bill down the road. It’s a smart way to safeguard your equipment, much like our Service Maintenance Programs protect your system long-term.
Tools and materials you’ll need
Beyond the main components, you’ll need a few specific tools and materials. This includes wire strippers, screwdrivers, pliers, a multimeter for testing connections, and the correctly sized electrical wire and conduit. However, running electricity from your home’s electrical panel to the outdoor unit is a serious task. It requires a deep understanding of electrical codes and safety procedures. If you have any hesitation, it’s always best to call a professional. You can even schedule one of our Virtual Tele-Tech appointments to get an expert evaluation before you start. Your safety is always the top priority.
How to Read a 220v Mini Split Wiring Diagram
Think of a wiring diagram as a roadmap for your mini split’s electrical system. It shows you exactly how every component connects to get power and communicate. While it might look like a complex web of lines and symbols at first, breaking it down into smaller parts makes it much easier to follow. The diagram is your single most important guide to a safe and correct installation, showing the path from the power source to the outdoor and indoor units. It details every connection, including the high-voltage power lines and the low-voltage communication wires that allow the system to function as one.
Before you even think about touching a wire, locate the diagram on your specific mini split unit, which is often on the inside of the outdoor unit’s access panel. Generic diagrams you find online are helpful for learning the basics, but they might not match your model perfectly. Always trust the manufacturer’s diagram on the unit itself to ensure you’re making the right connections. Electrical work can be tricky, and a small mistake can lead to big problems. If you look at the diagram and feel even slightly unsure, it’s always the smartest move to call in a professional. Our team is always ready to help with expert residential HVAC installations to get the job done safely and correctly.
Understanding the basic layout
When you first look at a mini split wiring diagram, you’ll see symbols representing the different components—like the indoor unit, outdoor unit, compressor, and fans—and lines showing the paths the wires take. The layout is designed to give you a clear visual of the entire electrical circuit. It shows where the main power comes in, how it’s distributed to the outdoor and indoor units, and how the communication wires link everything together. Take a moment to identify the main parts and trace the flow of power from the source to the components before you try to follow any individual wires. This initial orientation will make the rest of the process much clearer.
Decoding wire color codes
In the US, 220v or 240v circuits typically use specific colors to identify each wire’s function, which helps prevent dangerous mix-ups. The black wire is one of the “hot” wires, connecting to the L1 terminal. The red wire is the second “hot” wire, connecting to the L2 terminal. The ground wire, which is a critical safety feature, will be either green or bare copper. A key thing to note is that many 208/230v mini splits don’t require a neutral (white) wire because they run exclusively on 240 volts. Always check your unit’s specific diagram to confirm which wires you’ll need to connect.
Connecting L1, L2, and ground wires
Making the right high-voltage connections at the outdoor unit is fundamental for your system to operate. The diagram will clearly label the terminals where your main power supply connects. You’ll connect the black wire from your power supply to the terminal marked L1. Next, connect the red wire to the L2 terminal. Finally, attach the green or bare copper ground wire to the designated ground screw or terminal. This grounding step is essential for safety, as it protects the unit and you from electrical faults. Double-check that each connection is tight and secure before moving on, as loose connections can cause serious issues.
Wiring the power supply to the disconnect switch
Your mini split needs its own dedicated circuit to prevent overloading your home’s electrical system and tripping breakers. The power from your main breaker panel first runs to an outdoor disconnect switch. This switch is a crucial safety feature that allows you to completely shut off power to the unit for maintenance or repairs. You’ll run the appropriate gauge wire from a dedicated two-pole breaker in your panel to this switch. From the disconnect switch, you’ll then run another set of wires to the outdoor unit’s L1, L2, and ground terminals, completing the high-voltage connection.
Connecting the indoor and outdoor units
The indoor and outdoor units need to communicate to regulate temperature, and they do so through a multi-conductor cable. Most mini splits use a 14/4 stranded wire for this connection, which contains four separate wires inside a single protective jacket. Typically, two of these wires provide low-voltage power to the indoor unit, one is for communication signals, and the fourth is a ground wire for safety. The wiring diagram will show you exactly which numbered or colored terminals on the outdoor unit correspond to the terminals on the indoor unit, ensuring they can work together seamlessly.
How to Wire a 220v Mini Split: A Step-by-Step Guide
With your wiring diagram in hand, you’re ready to tackle the installation. This guide breaks down the process into manageable steps, but remember, working with 220-volt electricity is serious business. Your safety is the top priority. Always turn off the power at the main circuit breaker before you begin and double-check that it’s off with a voltage tester.
This process requires a solid understanding of electrical work. If you feel unsure at any point, it’s always best to call in a professional. A licensed electrician or a certified HVAC technician can ensure your system is installed safely and correctly, giving you peace of mind. At QRC, our team handles these installations every day, ensuring every connection is secure and up to code. We provide expert residential HVAC services that you can count on for a safe and efficient setup.
Prepare your electrical connections
First things first, you need to get power to your outdoor unit. Most 220v mini-split systems require a dedicated 208/240-volt circuit run directly from your home’s main electrical panel. This isn’t a job for an extension cord; it needs its own circuit breaker to handle the load safely. Before you start, shut off the main power supply to your entire house. Once the power is off, you’ll run the appropriate gauge wire from a new, correctly sized double-pole breaker in your panel to the location of the outdoor unit. Always check your local electrical codes to ensure your plan is compliant.
Install the disconnect switch
Every outdoor HVAC unit needs a disconnect switch. This is a non-negotiable safety feature required by code. You must install a disconnect switch on the exterior wall, within sight of and right next to the outdoor unit. This switch allows you or a technician to safely cut power directly at the unit for repairs or maintenance without having to go back to the main panel. Mount the weatherproof box securely, then run the power cable from your main panel into the line-side terminals of the switch. Make sure your connections for the two hot wires (L1, L2) and the ground wire are tight and secure.
Connect the outdoor unit
Now it’s time to link the disconnect switch to the outdoor condenser. You’ll use a short, flexible, weatherproof conduit called an electrical whip for this step. The whip protects the wires from moisture, sun, and physical damage. Attach one end of the whip to the disconnect box and the other to the electrical access point on the outdoor unit. Feed the wires from the load-side of the disconnect switch through the whip and connect them to the corresponding L1, L2, and ground terminals on the condenser. Refer to your unit’s wiring diagram to get this right.
Wire the indoor unit
Next, you’ll connect the indoor and outdoor units so they can communicate. Most mini-splits use a 14/4 stranded conductor cable for this connection. A 14/4 cable contains four wires: two for power, one for communication, and a ground wire for safety. You’ll run this cable from the outdoor condenser to the indoor air handler, often alongside the refrigerant lines. Carefully connect each wire to the numbered terminals on both units, ensuring they match perfectly—terminal 1 on the indoor unit must connect to terminal 1 on the outdoor unit, and so on. Mismatched connections will prevent your system from working.
Place the refrigerant lines correctly
While not strictly an electrical step, the placement of your refrigerant lines is done at the same time as the wiring and is just as important. When you mount the indoor unit, make sure it’s on an exterior wall with at least six inches of clear space above and to the sides for proper airflow. This positioning also simplifies running the line set—which includes the refrigerant lines, communication wire, and condensate drain line—through the wall to the outdoor unit. Bundling these components together keeps the installation neat and protected as they pass from inside to outside.
How to Stay Safe During Installation
Working with a 220v system is a serious task, and your safety should always be the top priority. While understanding the wiring diagram is a huge step, the actual installation requires careful attention to detail to prevent electrical shock, equipment damage, or fire hazards. It’s not just about connecting wires; it’s about creating a secure and lasting electrical connection. Before you start, you need a solid safety plan. This means shutting down power correctly, using the right gear, and knowing your limits. A successful DIY project is one where everyone stays safe. Let’s walk through the essential safety steps you absolutely can’t skip.
Following power shutdown procedures
This is the most critical step. Before you touch a single wire, you must turn off the main power at your electrical panel. Find the main breaker that controls power to your entire home and switch it to the “OFF” position. This prevents any electricity from flowing while you work. For an extra layer of safety, use a voltage tester at the circuit you’ll be working on to confirm the power is completely off. It’s also a good idea to place a note on the panel so no one turns it back on.
Using the right safety equipment
Protecting yourself and your new mini split is essential. Start with personal protective equipment (PPE), like safety glasses and insulated gloves. Beyond personal gear, you should also protect your equipment. Mini splits are a big investment, and a surge protector is highly recommended to shield the system from sudden power spikes, like those from a lightning storm, which can fry the sensitive electronics inside. Using properly insulated tools also reduces the risk of accidental contact with live circuits if the power were to be turned on by mistake.
When to call a professional
Installing a mini split involves significant electrical know-how. If you’re not completely comfortable with any part of the installation, especially the high-voltage work, it’s always best to hire a professional. An incorrect connection can damage your new unit, create a fire hazard, or lead to serious injury. A licensed technician will ensure the job is done right and meets all local electrical codes. At QRC, our team handles complex residential HVAC installations every day, and we’re here to help you get it done safely and efficiently.
Testing Your 220v Mini Split’s Electrical Connections
You’ve run the wires and connected the units. Now comes the moment of truth: testing your work. This final step is about verifying that every connection is safe, secure, and ready to provide reliable comfort. A few careful checks now can prevent major headaches later, ensuring your system runs efficiently from day one. Let’s walk through the proper procedures to test your new mini split.
Post-installation testing procedures
Before restoring power, do one last safety check. Confirm the main power at your electrical panel is still off. Visually inspect every connection you made—at the disconnect switch, the outdoor condenser, and the indoor air handler. Are all the screws tight? Is any copper wire exposed? Everything should be snug and secure. This is also your chance to confirm the outdoor disconnect switch is properly sealed. If you have any doubts about your work, it’s always best to get a professional opinion from a trusted residential HVAC expert.
Your system startup checklist
Once you’re confident in your connections, it’s time to power up. Turn the circuit breaker back on, then switch on the outdoor disconnect. Now, put the system through its paces. Run it on its highest heat setting for 15 minutes, then switch to its coldest air conditioning setting for another 15 minutes. This tests both cycles. While it’s running, listen for strange sounds and check for steady airflow from the indoor unit. Consistent performance is key to long-term reliability, which is why regular upkeep through service maintenance programs is so important.
How to identify wiring problems
What if the unit doesn’t turn on or immediately trips the breaker? First, turn all the power back off. A tripped breaker often points to a short circuit or an overloaded circuit. A common issue is using the wrong wire gauge; thinner wires can’t handle the electrical load of a 220v system, creating a fire risk. Also, check your unit’s specific needs. If it only has L1, L2, and ground connections, it runs purely on 240 volts without a neutral wire. For persistent issues, our Virtual Tele-Tech appointments are a great way to get expert eyes on the problem quickly.
Common Wiring Mistakes to Avoid
Wiring a 220v mini split isn’t just about connecting the dots on a diagram; it’s about doing it safely and correctly to ensure your system runs efficiently for years. A few common slip-ups can lead to major headaches, from a system that won’t turn on to serious electrical hazards. Even if you’re comfortable with home projects, it’s easy to overlook a small detail that has big consequences.
Getting the wiring right is the foundation of a successful installation. It protects your investment, your home, and your family. Below, we’ll walk through the four most frequent wiring mistakes we see and explain how you can steer clear of them. Paying close attention to these details will help you avoid performance issues and ensure your mini split operates just as it should. If you ever feel unsure about a step, remember that professional HVAC technicians are trained to handle these connections safely.
Using the wrong wire size
Choosing the right wire size, or gauge, is one of the most critical steps in this process. Think of a wire like a pipe for electricity—a bigger pipe can handle more flow. Electrical wire gauge works in reverse, so a lower number means a thicker wire that can carry more electrical current. Using a wire that’s too thin for your mini split’s needs is a serious fire risk. The wire can overheat, melt its protective coating, and potentially ignite surrounding materials. Always check your unit’s manual for the manufacturer’s specifications on the required wire gauge and circuit amperage to ensure you’re making a safe choice.
Grounding improperly
The ground wire is a crucial safety feature that should never be overlooked. It provides a safe path for electricity to travel in case of a short circuit, protecting you from electric shock and preventing damage to the unit. Most mini splits use a specific cable, often a 14/4 conductor cable, which includes two power wires, a communication wire, and that all-important ground wire. An improper or missing ground connection leaves your system vulnerable and creates a significant safety hazard. Make sure the ground wire is securely fastened at the unit, the disconnect switch, and the breaker panel according to the wiring diagram.
Skipping the disconnect switch
A disconnect switch is a non-negotiable part of any mini split installation. This is an external switch, typically installed in a weatherproof box on the wall near your outdoor condenser unit. Its purpose is simple but vital: it allows you or a technician to completely cut power to the unit right at the source. This is essential for performing safe maintenance and repairs. Local electrical codes almost always require a disconnect switch, so skipping it not only creates a safety issue but can also cause you to fail an inspection. Don’t treat it as an optional add-on; it’s a required safety component.
Making poor electrical connections
Even if you use the right wire and install all the components, a loose connection can undo all your hard work. Poorly secured wires can cause electrical arcing, lead to power loss, or make your system operate erratically. Over time, vibrations from the unit can cause loose connections to worsen, creating a potential fire hazard. Take your time to ensure every wire is securely fastened to its terminal. Some manufacturers even recommend using special crimp terminals for a more solid and reliable connection. Double-checking that every screw is tight and every wire is snug is a final step that ensures your system’s long-term health and safety.
How to Troubleshoot Electrical Issues
Even with a careful installation, your mini split system can sometimes run into trouble. When electrical issues pop up, the system will often tell you what’s wrong through error codes on the display. Think of it as your mini split’s way of asking for help. By understanding what these codes mean and where to look for common problems, you can often identify the source of the issue.
Before you start, always remember to shut off the power at the breaker and the disconnect switch. Safety is the top priority when working with any electrical system. While some of these steps can help you diagnose a problem, complex electrical work should always be handled by a qualified technician. If you ever feel unsure, it’s best to call for professional HVAC and refrigeration service.
What error codes mean for your wiring
Your mini split’s error codes are the fastest way to figure out what’s going on. For example, an EL01 or E1 error code usually points to a communication problem between the indoor and outdoor units, which is often caused by a wiring issue. Other codes can signal different problems, like an E3 error indicating a fan motor malfunction or an E4/E5 error pointing to a sensor failure. Learning to recognize these codes helps you narrow down the possibilities. Instead of guessing, you can use the code as a starting point to inspect the specific wires and connections related to that function.
Dealing with voltage fluctuations
A mini split needs a steady, correct voltage to run properly. When the power supply fluctuates, it can cause serious damage. Your system might display an F0 or P1 error code to warn you about overvoltage or undervoltage. These issues often happen when the unit is wired incorrectly. A 220v system requires two hot wires and a ground wire connected to the right terminals. If these connections are wrong or if your home’s electrical supply is unstable, it can lead to system shutdowns or component failure. If you suspect voltage issues, it’s a good idea to have a professional check both your unit’s wiring and your home’s electrical panel.
Fixing common connection problems
More often than not, electrical problems come down to a simple loose or incorrect connection. Wires can sometimes work themselves loose over time due to vibrations, or they may not have been secured properly during installation. For instance, an improperly connected neutral wire can trigger a range of seemingly unrelated error codes. Start by visually inspecting all the terminal blocks on both the indoor and outdoor units. Make sure every wire is securely fastened and that there are no signs of corrosion or damage. If you’re getting a communication error, pay special attention to the wire that links the two units together.
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Frequently Asked Questions
Why would I choose a 220v mini split over a 110v one? Think of it in terms of power and purpose. A 110v mini split is great for a small, single room, like a home office or a small bedroom. A 220v system, however, packs more punch. It can handle much larger spaces, like an open-concept living area, a workshop, or even multiple rooms. Because it runs on a higher voltage, it operates more efficiently, which can save you money on energy bills over time. If you need a robust solution for a larger area, the 220v model is almost always the right choice.
Do I absolutely need a dedicated circuit for my mini split? Yes, this is a non-negotiable safety requirement. Your mini split is a powerful appliance that draws a significant amount of electricity, especially when the compressor kicks on. Putting it on a shared circuit with other outlets or lights would constantly overload the circuit, causing the breaker to trip. A dedicated circuit ensures the unit gets the consistent power it needs to run safely and efficiently without interfering with the rest of your home’s electrical system.
I’m pretty handy. Can I handle the wiring for my 220v mini split myself? While it can be tempting to tackle the wiring yourself, working with 220-volt electricity is a serious task that carries significant risks. This isn’t like swapping out a light fixture. An incorrect connection can damage your new system, create a fire hazard, or lead to severe electrical shock. Unless you are a licensed electrician or have extensive experience with high-voltage residential wiring, this is one job that is always best left to a qualified professional.
What’s the most common mistake people make when wiring their mini split? The most dangerous mistake is using the wrong size wire. The thickness of the wire, or its gauge, must be able to handle the electrical current your mini split draws. Using a wire that is too thin is a major fire hazard because it can overheat and melt its protective insulation. Always follow the manufacturer’s specifications in your unit’s manual to the letter when selecting your wire gauge.
My mini split isn’t working after I wired it. What’s the first thing I should check? First, for your safety, turn the power off at both the main breaker and the outdoor disconnect switch. Once you’re sure the power is off, do a simple visual inspection. Check every connection point—at the indoor unit, the outdoor unit, and the disconnect switch. Make sure every wire is securely fastened in its terminal and that the communication wires match up correctly between the indoor and outdoor units. A single loose wire is often the culprit.