Top 10 AC Installation Mistakes

Installing air conditioning systems is complex, even for replacement systems. Customers (and sometimes technicians who are not well trained) underestimate the knowledge required to get it right. AC installation mistakes are common, and can lead to performance issues down the road.

In fact, a reliable air conditioning system depends as much on the quality of the installation as on the quality of the equipment. 

Junior technicians: learn about the most common AC installation mistakes so employers and customers can count on you to do the job properly.

10 AC installation mistakes and how system performance suffers

1. Failure to remove moisture

Before charging the system with refrigerant, proper AC installation procedure includes vacuuming the system to remove air and moisture. 

Don’t skip this step, because moisture in the system can cause corrosion, performance problems, excess energy usage, a frozen coil, or increased pressure leading to a failed compressor.

2. Inaccurate refrigerant charge

It’s essential to follow manufacturer instructions for refrigerant levels for the specific model you’re installing. 

An undercharged unit won’t cool properly, and an overcharged unit will be noisy (turning on and off frequently), fail to control humidity, and draw excess power. Never assume how much refrigerant is needed: consult the manufacturer’s guidelines before doing the installation.

3. Failing to insulate refrigerant lines

In split system air conditioners, the components are connected by refrigerant lines that are exposed to outdoor weather. Installers sometimes take a short cut and fail to protect the refrigerant lines with proper insulation. 

This mistake makes the system work harder and work less efficiently, leading to excess energy consumption, poor performance, and shorter system life.

4. Poor thermostat location 

Thermostats installed in the wrong location can give inaccurate signals to the system, resulting in too much or too little cooling. 

Thermostats must be placed away from heat sources, such as cooking appliances, fireplaces, and sunlight, as well as drafts from windows or doors. They should be installed at a height of 52 to 60 inches, since heat rises and higher locations can result in misleading readings.

5. Poor condenser placement & clearance

Outdoor condensing units also need to be placed in the right location: in a shady spot where it’s not exposed to direct sunlight or pooling water. It’s also best not to place directly under a tree where falling limbs can cause damage. 

The unit also needs at least 2-3 feet of clearance around it (and 5 feet above it) to ensure proper air flow. With multiple commercial units installed together, leave 2 to 4 feet between them (as per manufacturers’ instructions).

In the wrong location, the unit needs to work harder to cool, reducing system life span and potentially causing compressor failure.

6. Poor supply and return vent placement

If you’re installing new ductwork, the placement of supply and return vents is critical for optimized system performance. They need to be strategically positioned according to the usage and occupancy of the space.

Installers often fail to think about how people use and furnish homes and commercial spaces. Vents need to be kept open and unimpeded for proper air flow (more on that next). So ideally, place AC vents at the top of the wall where they won’t be blocked by furniture. Remember, cool air sinks, so conditioned air will move where it needs to be.

7. Insufficient air flow

Proper air flow is essential to AC performance. As part of the equipment installation process, you must always adjust fans, dampers and registers to provide adequate airflow throughout the space. 

Failure to complete this step causes spotty performance, with areas that are too cold or too warm. The system works harder than it has to to reach the set temperature, driving up energy costs and reducing the life span of the system.

8. Inadequate drainage

If you don’t provide a proper drainage system to remove condensate produced in the cooling process, the customer will end up with water damage in their space. That can destroy walls, ceilings, floors, expensive finishes, furnishings and personal belongings. In the worst case, accumulated moisture can lead to mold growth that can harm people’s health.

That means drain lines and pans need to be correctly installed to prevent water leaks.

9. Not sealing ducts

When HVAC ducts are not sealed, conditioned air leaks out through tiny holes and cracks, where it’s wasted inside the walls and crawl spaces. 

That means it never reaches the occupied space. The result is insufficient cooling. The unit also works harder and runs longer trying to reach the set temperature, which drives up energy costs and increases wear and tear on the system.

10. Not checking for refrigerant leaks

Installations can be tricky, and small refrigerant leaks can happen. That’s why you must always check the coils carefully for leaks upon completion of the installation. If you miss one, the customer will be calling before too long to complain about their new AC not cooling properly.

Technicians: a simple way to improve your knowledge & skills

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HVACR Career Connect NY was created to promote the exceptional quality-of-life benefits of a career in HVAC and Refrigeration service, and also to provide a clear path for getting started in the profession. In doing so, we serve as a resource for employers in the New York City metro area to find and hire smart and capable new technicians. We also serve as an educational resource to support business growth and to help service technicians succeed in their chosen profession.