Why is steam coming off my mini split outdoor unit in winter?

That's usually the defrost cycle. In heating mode the outdoor coil frosts over, so the system reverses briefly to melt it. You'll see steam and water, the outdoor fan may stop, and the indoor fan pauses so it doesn't blow cold air. A few minutes later it goes back to heating.

What does a blinking light or error code on my mini split mean?

It's the unit telling you what it detected — communication faults, sensor faults, high or low pressure protection, compressor or inverter faults, fan motor faults, drain/float faults, and voltage protection are the common families. Codes are different for every brand, so look up your exact model's service manual. Power-cycling may clear it temporarily, but if it comes back, the cause is still there.

Real field troubleshooting · 20 years on mini splits

Mini split acting up? Let's find out why.

Q: Why is my mini split running but not cooling?

Start with the simple stuff: make sure the remote is in Cool (not Fan, Dry or Auto), clean the indoor filters, check that the outdoor unit is running and its coil isn't packed with dirt, and confirm nothing is blocking the outdoor unit. If those check out, the most common causes are a dirty indoor coil or blower wheel, low refrigerant from a leak, or a failed sensor, fan motor or board — which needs a technician with gauges and a meter.

Q: Why is my mini split leaking water inside?

Almost always a condensate problem: a clogged drain line, a drain line that bellies or runs uphill, an indoor unit that isn't level, or a dirty coil and filters. A cassette or ducted unit can also have a failed condensate pump. Clear the drain, check the pitch, and clean the unit.

Q: Is it normal for a mini split to click, hiss or crackle?

Yes, some sounds are normal. Plastic panels tick as they expand and contract, the expansion valve clicks at startup, and you'll hear a hiss or whoosh when refrigerant flow changes or during defrost. Grinding, squealing, loud rattling or banging are not normal and point to a fan, blower wheel, loose part or mounting problem.

Q: How often should a mini split be cleaned?

Rinse or vacuum the indoor filters every 2–4 weeks during heavy use. Have a deep cleaning of the indoor coil and blower wheel done at least once a year — more often with pets, smokers, or in kitchens — and keep the outdoor coil clear of dirt, leaves and grass clippings.

Not cooling, not heating, leaking, noisy, shaking, or blinking a code — here's what I check first on every service call. When you're ready to learn the whole system, I'll teach you everything at MiniSplitTraining.com.

Start Mini Split Training → Troubleshoot my unit

274K+ YouTube subscribers 20 yrs in the field Licensed TN mechanical contractor

What's your mini split doing?

🥵Not cooling 🥶Not heating 💧Leaking water 🚨Blinking / error code 🔊Making noise 📳Shaking / vibrating 🦠Smells / dirty 🔌Won't turn on

Step 1 · Diagnose

How to diagnose a mini split problem

Start with what you can see and check safely. Most of my calls end up being airflow, drainage, or dirt — not a dead compressor. If the simple checks don't fix it, that's where real training (or a real tech) comes in.

🥵Not cooling

Remote set to Cool — not Fan, Dry, or Auto — and set below room temp.
Pull and clean the indoor filters. Clogged filters are the #1 call.
Is the outdoor unit running? Fan spinning, coil not matted with dirt or cottonwood?
Ice on the indoor coil or the copper lines = airflow or charge problem. Turn it off and let it thaw.
Weak airflow with clean filters = dirty coil or blower wheel.

🔧 Still warm after all that? Low charge from a leak, a bad sensor, fan motor, or board. That takes gauges, a meter, and know-how.

Learn the full diagnosis in Level 3: Repair

🥶Not heating

Remote in Heat mode with the setpoint above room temp.
Indoor fan stops for a few minutes and the outdoor unit is steaming? That's defrost — normal.
Indoor fan won't start right away in heat? Many units wait for the coil to warm up first (cold-draft protection).
Outdoor unit buried in ice or snow? Clear it — never chip ice off the coil.
Check the unit's minimum heating temperature. A standard unit loses a lot of capacity in hard cold; cold-climate units are built for it.

🔧 Heats weak all the time, or blows cold in heat mode? Could be charge, the reversing valve, or a sensor — tech territory.

See how heat pumps really work in Level 1

💧Leaking water inside

Clogged drain line — slime and dirt build up. Clear it with a wet/dry shop vac at the outside end.
Bad drain pitch — the line has to run downhill the whole way. A belly or uphill section traps water.
Head not level — the drain pan side should sit slightly low so water runs to the drain.
Dirty coil / filters — water blows off the coil instead of dripping into the pan.
Cassette or ducted unit? Check the condensate pump and float switch.

💡 Water spitting out of the vents is usually a dirty blower wheel or coil, not a leak.

Learn drain cleaning in Level 2: Maintenance

🚨Blinking light or error code

Write down the code or count the blinks before you reset anything.
Codes are different for every brand — look up your exact model's manual.
Common code families: communication, sensor/thermistor, high or low pressure, compressor/inverter, fan motor, EEV, drain/float, voltage protection.
Kill power at the disconnect for 5 minutes and restart. If the code comes back, the problem is still there.

🔧 A code tells you where to look, not which part to buy. Techs: test before you replace.

Learn to read any fault code in Level 1

🔌Won't turn on

New batteries in the remote. Point it at the indoor unit's receiver.
Check the breaker and the outdoor disconnect.
Many units have a manual/emergency button under the front panel — try it.
Recent storm or power outage? Surges kill boards. A surge protector / line voltage monitor is cheap insurance.

⚠️ Inverter boards hold high DC voltage even after power is off. Don't open the outdoor unit unless you're trained.

Learn board and power testing

🔁Runs and shuts off / short cycles

Oversized unit — too big for the room cools fast, shuts off, and never pulls the humidity out. Clammy room = classic sign.
Indoor unit blowing air straight into a wall or furniture reads the wrong temp.
Dirty outdoor coil can trip high-pressure protection on hot days.
Low voltage or a weak circuit can trip voltage protection.

💡 Sizing mistakes can't be fixed with a part. Size it right the first time.

Learn sizing in Level 4

Step 2 · Is it dirty?

How to tell if your mini split is dirty

A filter rinse isn't a cleaning. The coil and the blower wheel behind it collect gunk that a filter never stops — and that's what causes smells, weak air and water problems.

Musty or "dirty sock" smell when it kicks on — mold and bacteria on the coil or blower wheel.
Black specks on the vanes or the wall under the unit — that's growth being thrown off the blower wheel.
Weak airflow even with clean filters.
Water spitting from the vents or dripping down the wall.
Shine a flashlight up into the vent — if the blower wheel's blades look fuzzy or black, it's due.
Outdoor coil looks matted with dirt, pollen, leaves or grass clippings.

How I keep them clean

Filters: rinse every 2–4 weeks during heavy use. Let them dry before putting back.
Deep clean once a year (more with pets, smokers, kitchens): wash bag on the indoor unit, foaming coil cleaner, rinse the coil and blower wheel.
Cassettes: clean the condensate pump and drain while you're in there.
Drain line: shop-vac it from the outside end every year.
Outdoor unit: rinse the coil from the inside out, keep 12"+ of clear space around it.

Always kill the power at the breaker and disconnect before cleaning. Protect the board and the motor from water.

Watch the full cleaning lessons →

Step 3 · Sounds & vibration

Why is my mini split making noise or shaking?

Some sounds are normal. Some mean a part is on its way out. Here's how I sort them out on a call.

What you hear / feel	Most likely cause	What to do	Verdict
Ticking or crackling	Plastic panels expanding/contracting as temps change.	Nothing — normal.	Normal
Hiss or "whoosh"	Refrigerant flow changing at startup, shutdown, or during defrost.	Normal if it's brief. A constant hiss at a fitting can be a leak.	Usually normal
Clicking at startup	Expansion valve (EEV) setting itself, relays on the board.	Normal.	Normal
Gurgling / bubbling	Water fighting its way down a drain that's partly clogged or doesn't pitch downhill.	Clear the drain, check the pitch.	Fix it
Rattling indoors	Loose front panel or vane, debris or a broken piece in the blower wheel.	Power off, check the panel and blower wheel.	Fix it
Grinding or squealing	Fan motor bearings going out, or a blower wheel rubbing.	Shut it off — motor or wheel likely needs replacing.	Call a tech
Humming / buzzing	Loose panel or screws vibrating; electrical hum from a reactor or board.	Tighten panels. Loud or new buzzing — have it checked.	Check it
Outdoor unit shaking	Not level, loose mounting bolts, missing rubber isolation pads, ice or damage on the fan blade.	Level it, tighten mounts, add isolation pads, check the blade.	Fix it
Vibration through the wall	Line set touching the house or wall sleeve; no vibration/service loop in the copper.	Re-strap the lines so they don't touch; use proper isolation.	Fix it
Indoor unit wobbling	Mounting plate not secured into studs, or a dirty / out-of-balance blower wheel.	Secure the plate; clean the blower wheel.	Fix it
Banging / knocking outside	Compressor or fan problem, something loose inside the cabinet.	Turn it off and get it diagnosed.	Call a tech

Step 4 · Most problems start at install

Mini split installation tips that prevent callbacks

After 20 years I can tell you how an install went just by looking at the flares and the drain. These are the mistakes I see over and over.

Nitrogen pressure test

Pressure-test every joint with dry nitrogen before you pull a vacuum. Find the leak now, not next summer.

Pull a real vacuum

Use a micron gauge. Get down to 500 microns or lower and watch that it holds. "Ran the pump for 15 minutes" isn't a vacuum.

Flares & torque

Make clean flares with a good flaring tool and torque them with a torque wrench to spec. Over- or under-tightened flares are the #1 leak I find.

Condensate drain

Downhill the whole way — no bellies, no uphill runs. Level the head so water runs toward the drain side.

Clearances & placement

Follow the clearance specs above and around the indoor unit, and give the outdoor unit room to breathe. Keep it off the ground and out of drip lines.

Check line voltage

Verify voltage before startup, and add a line voltage monitor / surge protector. Bad power kills inverter boards.

Size it right

Bigger isn't better. An oversized unit short-cycles and leaves the room clammy. Do a load calc.

Service loop

Leave a vibration/service loop in the line set and keep the copper from touching the house.

Learn installation step by step → DIY install guide

For techs · Testing components

Testing mini split components the right way

Swapping parts until it works gets expensive. Here's how I approach the testing — the full step-by-step for every part is inside the course.

🌡️

Thermistors / sensors

Unplug at the board and read resistance with a meter. Compare to the unit's temperature chart — open, shorted, or way out of range means bad.

⚙️

Inverter compressor

Power off and wait for the board to discharge. Windings should read low and balanced across all three, and never to ground.

🌀

DC fan motors

Check the board's output voltages to the motor before you condemn it. A lot of "bad motors" are bad boards — and vice versa.

🔀

EEV coil

Check coil resistance and listen for it to drive at startup. A stuck EEV can look exactly like low charge.

📡

Communication

Verify the power and signal between the indoor and outdoor unit at the terminal block. Wiring mistakes cause a lot of comm codes.

📱

Remote control

Point it at your phone camera and press a button — if you see the IR light flash, the remote is sending.

⚠️ Inverter outdoor units carry high DC voltage on the board, and it can stay there after the power is shut off. Component testing is for trained technicians. If that's not you, call one.

Watch & learn

My most popular mini split videos

Real service calls, real units. Millions of views from techs and homeowners. The full course takes it from here.

Subscribe to Taddy Digest on YouTube

TADDY DIGEST

Mini Split
Training
How to size, install, maintain & repair mini split systems

James T. Fuller

The book

Want it in your hands? Get the book.

Everything I teach, in a full-color paperback you can keep in the truck. Real photos from the field, written for techs, students, contractors and homeowners.

How mini splits work — every component
Maintenance & deep cleaning
Component bench testing
Fault codes & troubleshooting
Sizing & choosing a system
Installation, charging & multi-zone
200+ practice questions + answer key
Full-color, real field photos

$39.99 Buy on Amazon →

All-Access members at MiniSplitTraining.com get the digital edition included.

MiniSplitTraining.com

Stop guessing. Learn the whole system.

Practical mini split training that trade school didn't give you — built from 20 years of real field calls. Five levels, video lessons, quizzes and a certificate.

Level 1How they work

Level 2Maintenance & cleaning

Level 3Repair & charging

Level 4Sizing

Level 5Installation

All-Access Annual — $299/yrBest value · everything unlocked

All-Access Monthly — $49.99/moCancel anytime

Start Mini Split Training →

FAQ

Mini split troubleshooting questions

Why is my mini split running but not cooling?

Start simple: Cool mode (not Fan, Dry or Auto), clean filters, outdoor unit running with a clean coil, nothing blocking it. If that checks out, it's usually a dirty indoor coil or blower wheel, low refrigerant from a leak, or a failed sensor, fan motor or board — that needs a technician with gauges and a meter.

Why is my mini split leaking water inside?

Almost always the condensate: a clogged drain, a drain that bellies or runs uphill, a head that isn't level, or a dirty coil and filters. Cassettes and ducted units can also have a failed condensate pump.

Is it normal for a mini split to click, hiss or crackle?

Yes. Panels tick as they expand and contract, the expansion valve clicks at startup, and you'll hear a hiss or whoosh when refrigerant flow changes or during defrost. Grinding, squealing, loud rattling or banging are not normal.

Why is steam coming off my outdoor unit in winter?

That's the defrost cycle. The outdoor coil frosts over in heating, so the system reverses briefly to melt it. The outdoor fan may stop and the indoor fan pauses so it doesn't blow cold air. A few minutes later it goes back to heating.

What does a blinking light or error code mean?

It's the unit telling you what it detected — communication, sensor, pressure, compressor/inverter, fan motor, drain/float or voltage problems are the common families. Every brand uses different codes, so look up your exact model. If the code comes back after a reset, the cause is still there.

How often should a mini split be cleaned?

Rinse filters every 2–4 weeks in heavy use. Deep clean the indoor coil and blower wheel at least once a year — more with pets, smokers or kitchens — and keep the outdoor coil clear.