Heat pump mini-split systems (photo of the mini split indoor head above) are amazing and resilient machines. They are very popular in homes with boilers and great for home additions that don’t have ductwork run to them. Just like any other heating or cooling appliance, however, they do have issues from time to time. In this article, we will go over the most popular circumstances that would cause the unit to stop blowing cool air. This means that the unit is running but the air is warm. 

Blocked air filters

Clean air filters are crucial to the performance of a mini-split heat pump. Without proper airflow, the unit cannot transfer heat properly from the outdoor condenser to the indoor evaporator coil. Lift up the lid and expose the filters. Remove the filters and rinse them with water in the sink until they are clean. (shown in the photo above) Before you reinstall the filters, take a look at the evaporator coil. 

Dirty evaporator coil

The evaporator coil (shown in the photo above) is located behind the filters. So before you reinstall the filters, this aluminum coil be will be exposed. If it is dirty, simply spray it with some water from a spray bottle. You may also use evaporator coil cleaner which is specifically designed to clean these coils. Never use any harsh chemicals on the coil, it will damage it and lose its efficiency. Once the coil is cleaned, reinstall the filters. 

Dirty blower wheel

If you haven’t had your mini-split maintained in a while and if you have animals or are a smoker in your home, the blower wheel will become packed with debris and cause a lack of airflow to the unit. The one shown in the photos above was experiencing no heat. To remove the blower wheel will take some patience but can be done in about an hour from start to finish to remove, clean, and reinstall. First, turn the power to the unit off. You need to remove the outer cover, this usually just unclips and pops right off. You may have a few screws toward the bottom, hidden by some plastic covers that need to be popped off. You may have to remove a couple of wire connections as well, depending on the unit. Once removed, you will need to remove the airflow louvers and then just let the drip tray hang. (shown in photos above) The wheel will then be held in by a bracket on the left side. Remove this but don’t lose the bushing that may pop out with the bracket. Pull out the left side of the evaporator coil to give enough room to pull the wheel out. Then on the right side of the wheel, there will be a set screw that needs to be loosened. Then just pull the wheel out from the left side and pull from right to left. Once it is out, spray it with some sort of cleaners like simple green or a degreaser. Let it soak then rinse and repeat till clean. While the wheel is soaking, wipe down all the plastic interior of the unit. Clean out and dust or mold that may have developed inside the unit, like the one shown above. Then just reverse the removal steps. A helpful hint is to take photos as you go, so you don’t forget what goes where. Also, be sure to consult your owner’s manual before you start any job that requires the removal of anything.

If you tried all of the above and had no luck, then the last thing that needs to be checked is the refrigerant pressures. Now checking your refrigerant pressures requires an R-410A gauge set and in some cases, an adapter. To check your refrigerant without gauges, you may be able to hook a clamp meter to the compressor wire and run the unit under a full load. Then take this reading and compare it to the amp range for the compressor. If it is low, then the unit is low on refrigerant and needs to be leak checked. You can do this by getting some dish soap and water and mixing them in a Windex bottle. Then spray the most likely locations for a leak on a mini-split system… The compression fittings. (shown in the photos above) These are the most common leak spots because mini-split line sets are sealed and one length from beginning to end. These are often over-tightened or the flare was done incorrectly. spray these locations and wait to see if bubbles for as they did in the images of these clients above. If they do, you can attempt to tighten the fittings down very gently. If the fittings are already very tight, they need to be taken apart and re-flared. unfortunately, this is no DIY task and will require a licensed technician to come, make the repair and refill the system with refrigerant. A leak is one of the most costly issues to deal with and can run anywhere from $400 to $900.00 with labor and refrigerant.

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