Why is my mini-split blinking and not cooling?

A blinking light on a mini-split's indoor unit is usually the system reporting a fault. It has detected a problem, such as lost communication between the indoor and outdoor units, a failed sensor, an overheated compressor or low refrigerant pressure, and stopped cooling to protect itself. The pattern of blinks is a code, and your model's manual tells you what it means.

What the blinking means

Most ductless systems run their own diagnostics. Trane says a Mitsubishi mini-split self-diagnoses when there is a problem: it may flash an error code on the remote control screen, and you may see blinking green lights on the indoor unit^[1]. The owner's manual lists what each code means, and in most cases an error code means you should call your HVAC company for service^[1].

Other brands work the same way. Most mini-splits communicate board faults through error codes on the indoor unit, whether a flashing light pattern or an alphanumeric sequence^[3]. LG notes that on its split systems sold in North America, error codes are shown by blinking LED lights rather than numbers^[2]. On LG's chart, for instance, five blinks of the heating LED means a communication failure from the indoor unit to the outdoor unit^[2]. LG shows two-digit codes with two lamps: in its example, after the second LED blinks 3 times, the first LED blinks 5 times, which reads as code CH53^[2].

Codes are set by each manufacturer, so never assume a pattern from one brand means the same on another.

What to check before you call

Write the code down first. Count the blinks on each lamp, note how fast they flash, and wait for the pattern to repeat. Any technician will ask for the pattern and the model number when you call. The model number is usually on a label on the indoor or outdoor unit.

Then rule out the simple causes of "not cooling":

• Settings. Make sure the unit is set to Cool and the temperature is several degrees below the room temperature^[5]. If the system is set to Fan Only, the compressor never receives a call to run^[3]. Lennox adds that the target temperature needs to be at least 3 to 5 degrees Fahrenheit away from the room temperature^[3].
• Filters. Clogged filters starve the coil of air. Cleaning the indoor unit's washable filters is owner maintenance; see how often a mini-split should be cleaned.
• The outdoor unit. Look for leaves or debris against it, and keep shrubs and other plants at least two feet away from the outdoor unit^[5].

A power reset can clear a one-off glitch. LG says an error code may be a temporary error due to unstable electricity supply^[2], and Carrier says resetting a mini-split can sometimes resolve a temporary control or communication issue^[4]. The owner's manual explains how to do it on your model. Try it once: LG says if the same symptom persists after a power reset, it should be checked by a service technician^[2].

The usual faults behind a blinking unit that won't cool

Lost communication between the units

The indoor and outdoor units talk over a communication wire, and when that link fails, the system stops. If it occurs right after installation, LG says to ask the installer to check that the communication cables are wired properly^[2]. On a system that has run for years, a technician checks the wiring, the connections and the boards on each end.

The outdoor unit is not running

If the indoor fan blows but the air never cools, look outside. Lennox lists the main reasons a mini-split compressor won't start as a power interruption, a misconfigured remote or thermostat, a worn capacitor, low refrigerant pressure tripping a safety switch, a malfunctioning control board, thermal overload, or a compressor at the end of its service life^[3]. Thermal overload has its own causes: the usual triggers for the compressor's thermal overload protector are dirty outdoor coils, restricted airflow around the unit, or sustained operation in extreme temperatures^[3], and after the overload protector trips, the system will typically attempt a restart somewhere between 30 minutes and two hours later^[3].

Low refrigerant

Low refrigerant means a leak. When the charge drops, a low-pressure safety switch shuts the compressor down before damage can occur^[3], which is why the unit stops cooling and may show a code. Whatever the brand, only a trained HVAC technician can find the leak, repair it, and recharge the system^[5]. A whistling or hissing sound near the indoor or outdoor unit is most likely a refrigerant leak^[6].

A frozen coil or a drain fault

Restricted airflow or low refrigerant can freeze the indoor coil. If you see ice on the mini-split, turn the system off and contact a qualified HVAC technician rather than trying to remove the ice^[7]. Water dripping from the head is a related problem; see why a mini-split leaks water inside.

When to call a licensed pro

Call when the code comes back after one reset, when the outdoor unit stays silent, when a breaker trips again, or when you see ice or hear hissing. A technician quoted by Carrier puts it plainly: "If the outdoor unit is not running, that usually indicates a more significant problem that should be evaluated by an HVAC professional."^[4]

Give the technician the code and the model number when you book. The fixes behind most codes are licensed work: attaching or detaching hoses and gauges, adding or removing refrigerant, and adding or removing components all require EPA Section 608 technician certification^[8]. In Virginia, no individual may engage in, or offer to engage in, work as a tradesman unless licensed^[9], and the Code defines a tradesman as anyone who does electrical, plumbing or heating, ventilation and air conditioning work for the general public for compensation^[10]. Check the business on DPOR's License Lookup^[11].

For what happens once the technician arrives, read what a mini-split repair visit involves, and for prices, what mini-split repair costs in Virginia. Browse more HVAC repair answers, see mini-split repair, or find licensed HVAC businesses in Blacksburg.

Tell us the code and what the unit is doing and licensed local HVAC businesses quote the repair.