A ductless mini-split air conditioner is a great way to efficiently cool a single room or an entire house without the need for ductwork. Ductless systems have an outdoor compressor linked by refrigerant lines to one or multiple indoor evaporator units mounted on walls or ceilings.
Compared to traditional central AC systems, mini-split units offer superior control, efficiency, and flexibility:
- Zone Control – Each indoor unit can be controlled independently to match the needs of each room. Only cool the rooms you need.
- Efficiency – Mini-split systems are over 30% more efficient than central AC.
- Flexibility – The indoor units can be installed in almost any room without the need for ductwork. Add units as needed.
However, to reap these benefits, the system must be sized, positioned, and installed correctly. Improper installation can negatively impact efficiency, capacity, airflow, longevity, and noise levels.
This guide will cover a typical installation from start to finish. Carefully following these instructions as well as the manufacturer’s guidelines will ensure your system performs as rated over the long term.
Tools & Materials Needed
Installing a mini-split air conditioner requires basic mechanical and electrical skills. Make sure to adhere to all local building codes as well.
Tools Needed
- Tape measure
- Level
- Stud finder
- Electric drill and bits
- Hole saw
- Pipe cutters
- Flaring tool kit
- Wire strippers
- Vacuum pump
- Manifold gauges
- Wrenches
- Locking pliers
- Voltmeter
Materials Needed
- Mounting hardware
- Refrigerant lineset
- Condensate drain kit
- Insulation tape
- Electrical supplies
- Additional refrigerant (if needed)
Preparing the Installation Site
Proper positioning of both the outdoor and indoor units is critical for performance and serviceability.
Outdoor Unit Location
When selecting the location for your outdoor unit, consider:
- Noise – Pick a location removed from bedrooms and common areas
- Accessibility – Allow sufficient space for service and airflow
- Sunlight – Avoid prolonged direct sunlight which reduces efficiency
- Drainage – Ensure water can properly drain from the unit
- Codes – Do not place underneath windows or too close to property lines
Ideally, place your outdoor unit on a concrete pad on a north or east-facing exterior wall that is easily accessible. Make sure the pad is completely level so the unit does not vibrate excessively when running.
Leave a minimum of 12 inches of clearance on all sides of the unit per manufacturer specifications to allow for sufficient airflow. Greater clearances are recommended if possible.
| Direction | Minimum Clearance |
| Front | 24 inches |
| Back | 12 inches |
| Sides | 12 inches |
| Above | 60 inches |
Indoor Unit Location
Proper placement of the indoor unit is just as important as the outdoor unit. When picking an installation location, consider:
- Mounting surface – Pick an interior wall with studs suitable for securely mounting the indoor unit.
- Condensate drainage – Ensure unit can properly drain condensate via gravity.
- Obstructions – Do not block airflow from unit or pathways to outdoor unit.
- Noise – Avoid mounting above quiet areas like bedrooms.
- Sunlight – Prevent prolonged direct sunlight on indoor unit.
- Codes – Do not install above electrical panels or in moist rooms like laundries.
Ideally, mount the indoor unit high on an interior wall in the main occupied space that needs cooling. This allows for natural circulation and efficient air distribution.
For standard 8 to 15 foot ceilings, the Center for Disease Control (CDC) recommends a minimum of 8 to 9 foot installation height measured from the bottom of the unit to the floor. Adjust as needed based on your ceiling height.
Installing the Outdoor Unit
Once you have identified the ideal exterior location with sufficient clearance, you can move onto mounting the outdoor unit:
- Construct concrete pad – The pad should measure a few inches wider and longer than the unit. Make it at least 4 inches thick. This prevents sinking or cracking over time.
- Position unit – Place the unit squarely onto pad. Double check side and top clearances meet specifications.
- Secure unit – Bolt the feet of unit into concrete pad. Most units have pre-threaded holes for this purpose. Use all mounting holes to prevent distortion from vibration.
- Install drain caps – Screw caps onto drain holes to prevent bugs and debris from entering unit. Make sure they do not restrict drainage.
- Level unit – Use a level to check unit on all sides. Shim the feet if needed to achieve level installation. Proper leveling helps prevent leaks and uneven wear.
With the pad constructed, unit bolted down, and shimmed to be completely level, you are now ready to move inside and install the indoor evaporator.
Installing the Indoor Unit
The indoor unit should be positioned on an interior wall near the rooms you wish to cool without any obstructions blocking airflow.
Follow these steps to safely mount your indoor evaporator:
- Mark stud locations – Use a stud finder to mark all stud locations. Ensure mounting screws penetrate into the studs safely supporting over 100 lbs.
- Mark position – Based on wall measurements and ceiling height, determine and mark the optimal center point for installation. Verify sufficient clearance for condensation and refrigerant lines to run unobstructed to the outdoor unit.
- Create mounting template – Tape the included paper mounting template centered around your marked position to the wall.
- Drill holes – Using the template as your guide, slowly drill out all holes noted for mounting and refrigerant lines. Drill on studs when possible.
- Mount bracket – Securely screw bracket into wall using at least 6 mounting screws penetrating at minimum 1 inch into the studs.
- Install unit – With a helper holding the unit, hang it onto the mounting plate hook brackets. Then feed refrigerant and condensate lines through the holes.
- Secure unit – Clip or screw the lower mounting brackets into the bottom of the unit, then connect remaining piping, condensate line, and electrical.
Take your time to ensure the indoor head is centered, level, and secure. This prevents vibrations, noise, and potential leaks over years of use.
Connecting the Refrigerant Lines
Once the evaporator and condenser are securely mounted, you can move on to connecting the refrigerant piping. This transports the heat transfer fluid between the outdoor and indoor units.
Follow these best practices for connecting refrigerant lines:
- Select lineset – Determine needed length using provided pipe sizing guidelines. Purchase refrigerant grade copper tubing in matching diameter. Ensure tubing is free of kinks or debris throughout entire length.
- Cut tubing – Using tubing cutters, neatly cut both ends of refrigerant pipes square and deburr. This allows for solid flared fittings.
- Flare ends – Using flaring blocks and yoke clamp tool, shape the end of each pipe into a flared bell-mouth profile. This mates securely with flared fittings.
- Connect piping – Apply PTFE thread tape to suction / smaller line threaded fittings. Hand tightens connections initially. Then use appropriate sized wrenches to tighten an additional quarter turn to prevent leaks. Avoid over-tightening.
- Insulate piping – Wrap entire refrigerant line set with foam compressor insulation for maximum efficiency and condensation control. Secure with zip ties or aluminum tape.
- Pressure test – Perform careful leak checks on all connections and system using heated nitrogen with digital gauge manifold. Repair any leaks found immediately with silver alloy brazing rods.
With refrigerant lines clearly labeled, properly insulated, pressure tested, and confirmed leak-free, you are ready for final electrical hookup.
Wiring the System
Take care when connecting your mini-split air conditioner system to mains power. Always verify proper voltage and amperage rating.
Follow these steps for safe electrical installation:
- Mount electrical panel – Securely attach outdoor electrical control box near service entry away from potential leaks. Do not energize yet.
- Run wiring – Route proper gauge dual conductor power wiring + ground from electrical panel through conduit to outdoor unit main electrical inlet. Allow sufficient slack.
- Connect wiring – Review wiring diagram supplied with units. Connect wires securely matching polarity and grounding. For hardwired connections, strip 8mm insulation, then apply development spade lugs. Tighten terminal screws firmly.
- Install disconnect – Mount a dedicated disconnect box adjacent to the condenser so power can be killed locally for lockout tagout safety during service. Use all-weather rated box with integrated fuse per local code.
- Connect low voltage – Run 18-3 low voltage interconnect wire from outdoor unit to indoor terminals. This carries power and control signals between the units. Connect firmly with wire nuts or quick splice connectors.
- Confirm voltage – With electrical panel off, use a DMM voltmeter to check for unintended voltage at all terminals and common earth ground. Verify no unexpected power is detected before proceeding.
With proper gauge wiring run through conduit and securely terminated, you are ready to finish the installation by testing system operation.
Testing and Commissioning System
Upon initial startup, a careful commissioning process ensures peak performance and identifies any potential issues needing correction:
- Check for leaks – Verify refrigerant piping remains free of leaks with additional pressure testing for a minimum of 30 minutes at greater than 150 PSIG using nitrogen. Fix any leaks.
- Evacuate air – Connect vacuum pump with refrigerant manifold to system. Open valves and evacuate entire refrigeration circuit to under 500 microns of mercury for 60 minutes minimum.
- Charge refrigerant – Disconnect vacuum equipment and charge system through low side port with precise amount of R410a refrigerant specified on unit label. Do not overcharge.
- Test modes – Power on and cycle through all functions – cooling, heating*, fan only – checking for normal operation noises and lack of vibration. Verify good airflow.
- Monitor pressures – During heating and cooling cycles, use manifold gauges to measure suction and discharge pressures. Compare to targets to ensure proper charge level and lack of blockages.
- Verify drainage – Operate in cooling mode for 15 minutes. Ensure condensate drains adequately and pan remains dry, preventing microbial growth.
- Check controls – Systematically test all wired and wireless controls to confirm desired operations, including temperature adjustment, fan speeds, and operating modes function per specifications across all seasons.
- Adjust position – Make any final adjustments to installation position and location to optimize airflow and sound levels within the space.
By methodically commissioning and testing all functions upon installation, you give the system the best possible start to provide years of energy efficient, trouble-free cooling and heating.
Also Read: DIY Air Conditioner Maintenance Tips for Efficient Cooling
Conclusion
Installing a DIY mini-split air conditioner system takes planning, patience, and attention to detail – but the personalized comfort and energy savings are well worth the effort.
By following the comprehensive installation process outlined above and always adhering strictly to the manufacturer’s recommendations, even first-time DIYers can reap the benefits of ductless technology in their home.
Carefully consider each installation decision – from placement, mounting, wiring, and testing. Rushing any steps can undermine performance down the road. But taking your time helps ensure your new system operates cleanly, quietly, and efficiently for decades.
Questions commonly arise on even straightforward mini-split air conditioner installs, so never hesitate to consult manufacturer tech support or local HVAC professionals when needed. While managing the project yourself saves on labor costs, it is well worth the minimal extra expense to have an installation pro inspect your work.
And be sure to share your finished mini-split air conditioner project online to give back to the active ductless owner community. Your experiences, lessons learned, and recommendations help encourage and educate the next generation of HVAC DIYers!