Mini Split Failures, Problems & Troubleshooting Guide

The most common cause of a mini split failure is improper installation. Whether you are experiencing an issue with your unit or just trying to learn how to do it right the first time around, this guide will take you through the most common problem with a mini split.

Mini Split Installation

Communication Issues

Using the proper mini split communication wire is critical to a properly functioning unit. While some manuals may only call for 18 gauge wire it is always recommended to use 14 gauge 4 conductor wire (14/4) for most systems. Most local codes require 14 gauge wire, so using something smaller will not pass inspection in many areas. The wire should be stranded, not solid core. Solid core wire has been known to cause more issues. Make sure the wire you select is rated for indoor and outdoor use. If you are installing a unit in a commercial application, an armored cable is usually required. As with anything, check your local electrical codes and consult an electrician to ensure proper installation.

Improper wiring can lead to the following common problems:

  • Poor Signal. Symptoms of poor signal include:
    • Inconsistent operation
    • Unit working in some modes, but not others
    • Outdoor unit powers up but indoor unit does not
    • Indoor unit has power, but will not operate
  • Damaged or destroyed boards or compressor
    • Improper wiring can cause other system components to fail and require replacement.
  • Odd or loud noises
  • Communication error codes being displayed
    • Error codes may be visible on the indoor unit or outdoor board
    • Look for a series of lights blinking or a special code displayed

Grounding Issues

Grounding is important for any device that contains electronics. An air conditioner is no different. The control boards used in a modern mini split system are very much a miniature computer. These boards are susceptible to power surges, stray electrical energy, and RF (radio frequencies). Grounding the outdoor unit helps prevent some of the stray energy from getting into the board.

If your condenser is not grounded properly, you may experience some issues, such as improper operation. Worst case, you can have board and/or compressor failure. Improper grounding can cause the same problems as no ground.

When wiring your system, make sure the connections are correct. Most systems will have a terminal block with L1, L2 and C. L1 and L2 are your hot lines. C is your common or ground. You can add a fourth wire to add an additional ground, which never hurts. Grounding the chassis of the condenser to a ground rod also adds an extra level of protection. If you use a grounding rod, check it on occasion for deterization.

If you are unsure about grounding, consult with an electrician.

Mini Split Line SetsRefrigerant Issues

All modern mini split systems use R-410A. This refrigerant is much more environmentally friendly than the older R-22. It operates at a much higher pressure than other refrigerants and requires special care to ensure a properly functioning system. Make sure that you are using the right gauges for R-410A.

Most systems come precharged with some refrigerant, but depending on the length of your line set, more might need to be added. The installation manual for your unit will specify the weight of refrigerant needed per foot of line set. Always follow these guidelines exactly. An improper amount of refrigerant can lead to many issues, including:

  • Too little of a charge
    • System may not run at all and may show an error code
    • The system may produce loud noises
    • It might not be able to maintain the temperature in the space
    • It might not properly dehumidify
    • It might only function in cooling mode but not in heating mode
  • Too much of a charge
    • System may not turn on
    • Loud noises can be heard from the unit.
    • Unit may not be able to hold the temperature or may overshoot the setpoint

The use of a proper line set is also critical to system performance. Each mini split system will specify the proper size line set it needs including the size of the pipes, the minimum and maximum length, and the maximum height difference between the indoor and outdoor unit. Trying to reuse an old line set that is not correct for your system will result in failure.

Line sets must be insulated. Unlike a central system, both lines require insulation. At least ½” insulation must be used to ensure proper performance. Make sure the entire line is insulated all the way up to the flair connections. No bare copper should be visible.

Always make sure to completely vacuum the lines before introducing any refrigerant into the system. Any contaminants in the lines could lead to severe damage to internal components or the system not working at all. It’s also important to pressure test the system. This will make sure that there are no leaks.

Live Voltage Issues

The vast majority of mini split units require 208/230 volt service, but there are some that will work with 115 volts. Always make sure that your system is connected to the proper voltage. Even if the system is correctly wired to the proper voltage, issues can still occur depending on your electric service. If too high or too low of a voltage is delivered to the unit, damage to the boards can occur. Check the voltage at the unit before starting up the system and make sure it is within the approved range that the manufacturer states. If your voltage is too high, too low, or often fluctuates you should use a surge protector to make sure your system components are protected.

Water Leaking at the Indoor Unit

If you discover water leaking from the evaporator of your mini split there are several areas to check to determine the cause of the problem.

If you have a wall mounted indoor unit, the drain line must be pitched down at least 5 degrees when leaving the unit and going outside. Otherwise, the water can drip back into the room. If the the drain line is properly pitched, then the next step is to check for clogs in the line. You can use a gallo gun to clear any obstructions in the drain line.

A condensate pump can be used in installations where you are not able to drain with gravity. If you have a condensate pump and are experiencing leaking, check to make sure the condensate pump is properly wired and functioning. Make sure that the pump is installed properly and is not pumping higher than its rated height.

Environmental Issues

The temperature outside can impact a mini splits performance. If you have a heat pump unit and are trying to use it in cold weather, there are a few steps you can take to make it perform better.

If your unit has an optional drain pan heater, adding this can increase the temperature range in which the unit will operate. A wind baffle can also provide some help. Make sure that if you are in a location that gets snow your unit is installed on a stand or wall mount that is above the snow. You should also remove any snow from the top of the unit before operating. Overly windy areas can also negatively impact the unit.

If you are trying to use cooling at low temperatures for server room or other environments that call for cooling all year long, make sure you purchase a unit that offers low ambient cooling. A wind baffle will expand the range of the unit. Some system are designed with extreme ranges in mind. Make sure you check your units specifications when looking for all year cooling.

Repair or Replace?

If you have just purchased a new unit and are experiencing any of the issues outlined here, call your installer immediately to get them sorted out. If you are having trouble with an older mini split, it may be time for a new one. Replacing boards or compressors on older systems can be expensive and time consuming.

LG and Daikin are the leaders when it comes to reliable, long lasting mini split units. Exceptional build quality and commercial grade components are backed by industry leading warranties. Let our experts help you choose the best new mini split for your application.

Mickey Luongo

Mickey is the resident heating and air conditioning expert.

66 Comments

Harry

about 1 year ago

Replaced both capacitors and mother board in condenser ...split ac unit w/one head unit inside. Still getting blinking red light and pulsating/flickering green light. Condernser will not come on...head unit opens and closes flap, but no fan! Thanks, Harry

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james

about 1 year ago

where to I find the reset button unit not responding to remote control

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Mickey Luongo

about 1 year ago

Most mini splits do not have a reset button.

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margaret

about 1 year ago

Hi, Our older unit (Mitsubichi mini split) suddenly will not heat. Everything else works well, fan cooler, dehumidifier but when we set it to heat, it turns off.

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Chuck Purce

about 1 year ago

During the heating mode, Is it normal for the condenser on the unit to have accumulated frost all around the exposed condenser? The weather overnight was in the 20’s.

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Mickey Luongo

about 1 year ago

Depending on the unit, this is possible. Some mini splits, especially older ones do not perform well in cold temperatures. If available for your unit, you may want to add a drain pan heater or wind baffle.

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Actman

about 1 year ago

Our mini splits Turboair TAS-09VH. Everything work except heat. Would you advice ? I have 3 of this identical machines. Can I swap part to troubleshoot ?

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Terry

about 1 year ago

I just had a 18000 and a 9000 split Comfortstar unit installed in my new addition and the units in heat mode continually go into df mode. This is a constant issue after 1 week of worryfree use. Both units do this. I have had the installer here 5 times and the last time he replaced the exchanger unit outside. To no avail, the problem still exists. Anyone with a reasonable explanation will be greatly appreciated. My addition is cold and i need this problem fixed

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Mickey Luongo

about 1 year ago

Depending on where you are located and how cold it has been, you may be reaching the lower limits of the system's heating capabilities. Also, the system probably needs a drain pan heater installed.

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Tom

about 1 year ago

Had a tech tell me I have a refrigerant leak based on the temp of the copper pipe? Is that a reliable way to troubleshoot? Said it should be 90-100 degrees higher than ambiant temp which sounds high for a mini split.

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Milo

about 1 year ago

I have a multi zone with 5 units 3 in the second floor (9000 + 9000 and 6000) and two in the first floor (15000 and 9000) , 4 of them work perfectly but the one of 15000 has always two lights on, like still working to reach the set temperature. Why??

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Milo

about 1 year ago

BTW, the unit of 15000 is in the dinning room that connect to kitchen and Living room. My question if is normal for a unit who feed 3 rooms to have the two lights ON all the time even if I lower the temperature. The other 4 units just turned ON the second light just during the time is trying to reach the temperature and go back to one light.

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Patty

about 1 year ago

Hi, we have two 4 unit panasonic systems in our home. All except one work fine. This one doesn't seem to put out much air, and makes a continuous annoying noise. It seems that it always has done it. Could it be the wiring? Reading through the article that makes the most sense. Past warranty and refuse to return to original company we purchased from. THANKS!

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Kristie

about 1 year ago

My units keep turning off at night. This just started and I have the timer turned off.

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Ellen Smith

about 1 year ago

Our Fujitsu mini-split is about 4 years old. It keeps failing to function & showing flashing lights. We have had our HVAC guy out about 10 times, but most of the time we have to turn it off, bang on the outside door and restart it. The unit is high up & no one is touching it. This is really annoying because room temp goes low and our plants are dying. Should we call another HVAC guy, get a new unit or just keep the ladder out and bang on it periodically? Thanks so much

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Mickey Luongo

about 1 year ago

The flashing lights are probably an error code. I would get a second opinion from a new service tech.

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David Roback

about 1 year ago

The mini split works, it heats and cools but the front door with not rise when the unit is turned on. The cogged wheel does not seem to be broken or chipped on the right rear side of the door. Any other ideas?

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Clem

about 1 year ago

I have a mitshubishi split air conditioner with two returns. One develops a brownish oily residue on the airflow blades. What could be causes this to occur? Other than that, it works just fine. I routinely clean filters and coils are clean. Mitsubishi customer service was of no help. I was told to contact my installer. I'm also looking for a part for the outside unit to stop a slow drip. One doesn't seem to exist. Thanks for any help.

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Barbara Porter

about 12 months ago

my son has a quad split ductless unit in his home in hawaii. the units in two of the bedrooms are not working the tech that the property manager had look at it says that one board is bad but they would have to replace all 4 at a cost of around $14,000. is this right or is someone trying to con him into spending more than he needs to?

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Mickey Luongo

about 12 months ago

That doesn't sound right. I would recommend getting a second opinion from another professional.

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Nancy Halstead

about 11 months ago

my Fujitsu mini split is flashing slowly in the operation and timer lights and the economy light is flashing rapidly. I tried tiring it off and on as well as reset the circuit breaker but the unit is still not working and all the lights are still flashing. how do i fix this?

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Mickey Luongo

about 11 months ago

I would recommend finding the service manual for your model. That will tell you what the blinking lights means and what the issue with the unit is.

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Ron

about 11 months ago

I have a mini split that the high side line is sweating. A tech once told me if that line is sweating it's likely the system needs a charge. We put our gauges on and it's spot on. What else can I look for, the lines sweating in an attic area and dripping through. Any help appreciated

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Marissa Binstock

about 10 months ago

My unit is showing d1 and not cooling at all. I can't find this error code any where online or in the manuals. Anyone have any idea? Thanks!

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Susan

about 10 months ago

My two year old LG inverter v has had two pumps to the attic replaced. They are meant to draw the water from the dehumidifier up two feet to the outside drain. Why do they fail. Northeast of Albany, MY said this is an aftermarket part not warrenteed

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Mickey Luongo

about 10 months ago

It sounds like you are talking about condensate removal pumps. I would ask your installer what kind they are using and consider switching to a more reliable brand like Sauermann or Refco. Those do have warranties.

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Susan

about 10 months ago

Mickey, Thank you for your advice. Susan

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AJ

about 10 months ago

I just had a new bryant mini split installed, I have the temp set at 72 but when i wake up in the morning it will be 65~ in the room. Is this normal? The installer told me it would shut off just like and AC when the set temp is reached.

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Mickey Luongo

about 10 months ago

It sounds like there may be an issue with one of the thermistors on your unit. I would ask you installer to check it out.

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Steve johnson

about 9 months ago

My wall mount unit leaks onto the floor there is a condensate pump does the line leaving the unit have to have fall to the pump?

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Mickey Luongo

about 9 months ago

The drain line could be clogged or the pump could have failed.

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Pat

about 9 months ago

On newly installed Carrier Split system only a couple of weeks old there is a harsh chemical smell ,sorta like melted plastic aroma that ruins the air in the room. This only happens during cooling , not heating. Not sure what causes it to happen. Only happens intermittently and then the air is fresh again. It is enough to make you open all the windows and air the room out till the next time it does it. That smell is never in the room if AC is not used. Any ideas on how to solve this issue would be appreciated. I don’t think the unit has had time to grow anything yet in the coils, could it be wiring / insulation / windings on a motor or other component getting hot but only during one of the cycles ... ? Is that the Odor of the Freon leaking out ( intermittently ? )

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Diane

about 9 months ago

I have a ComfortStar mini split 12,000 BTU. The indoor unit was just cleaned since the technician (who is unfamiliar with this brand) thought the problem was because it needed to be cleaned. The unit cools but the blower is barely blowing, certainly not as it use to. Any idea what the problem may be? Thank you.

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Anthony Gurrola He.

about 9 months ago

Hi Diane. It sounds like the Phillips screw that mounts the blower wheel to the motor shaft may need to be tightened down a little more.

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Rob Frantz

about 9 months ago

Just installed a comfort star mini split. After days it quick cooling. I’m guessing there must be a leak, but any other thing it could possibly be?

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Diane M

about 9 months ago

We had a fujitsu mini split installed last August. 3 times now, have had a non cooling issue. We’re told there was a leak, and now, same issue. Compressor doesn’t come on . At a loss. Not even 1 year old.

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Simon Page

about 8 months ago

I have a Daikin Mini Split and generally it works fantastic. I have noticed that when using the AC it seems to act like it is in AUTO mode. During the heat of the day, the AC is on and seems to be working correctly in cool mode (snowflake), however occasionally I open the windows when it cools off outside and I find it on in the morning and putting out heat when the temperature is cooler than the set point. Both of the head units are set the same way, so I don't think its a conflict between them.

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Dan Buckley

about 7 months ago

I have a Fujitsi mini-spit on my first floor. 1- 18,000 BTU indoor head in Living room, 2-9000 BTU heads in dining room and kitchen. The 18,000 unit seems to be lacking in production in AC mode. One of the 9000 units, which is placed on an opposite side wall seems to produce all the cold air. So much that I have placed this 9000 unit on fan ONLY mode and it still kicks out more cold than the 18,000 unit. Any reason why this may be happening?

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Mickey Luongo

about 7 months ago

The first thing I would recommend it checking for a leak in the system as it is the larger units that are affected first.

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Jonathan D Pryor

about 7 months ago

Have my LG Prestidge in AC mode and noticed that the fan seems to be running in low setting despite fact I set it to high. Why would this be?

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Danny

about 7 months ago

I purchase a carrier unit about 15 years ago . now the unit only comes on with the on and off button on the unit. Is it the remote and where could i get a similar one from> I look on line and can not find one

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David Walker

about 7 months ago

My ductless mini split outside unit condenser coil started leaking refrigerant. How does this happen?

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Judith

about 7 months ago

I’ve had a dual system mini split for five years that has worked fine. Lately they only work if they are both running and do not cool when they’re running separately. I can’t find any information on this I need help

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Ron Sturdy

about 7 months ago

My Friedrich mr12y1e stopped cooling overnight. Indoor evap seems OK. Blowing room air temp. Outdoor unit fan works and runs continuously but compressor won't start. Dual cap 5/50 370. I don't have a way to check cap. I can't belive the compressor went overnight. While I'm a not a hvac guy I was a journeyman machine maintenance/machinist. I have repaired many units over the years. Most of the time its the run cap or the evap fan. I downloaded the manual and searched online. I hate to replace the cap if some other failure is more likely. Any thoughts?

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Jeff

about 6 months ago

If you have a 3 cassette out side unit can you only hook up 2 of the casettes and it run right

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Mickey Luongo

about 6 months ago

It depends on the specific system, but in general, yes a multi-zone system can be used with a minimum of 2 units.

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dan Park

about 5 months ago

We have a compressor serving three indoor units. All the indoor units are showing the condensate image and not turning on. Any suggestions?

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Michael

about 5 months ago

The unit is a Seville and it cools fine but when you turn the heat on it goes to defrost mode and run and shows a code of PO And P4 the outdoor unit fan will come on when the codes appear and runs slow and then will kick off after about five seconds can you help with the problem

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Diane

about 4 months ago

My Willis air temp shows an H5 error. Can anyone tell me what this might be and a way to fix it. The unit is less than a year old but Canadians weather means we need heat.

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lynn althouse

about 4 months ago

Our split unit is running pretty much all the time. It is set for heat. It will run and heat then runs cool. Doesn't shut off when temp is met

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Patricia

about 4 months ago

I had my fujitsu mini-split installed less than 6 months ago. It has 2 wall mounted units - the smalled unit runs perfectly fine & never had an issue. The larger unit was incorrectly installed which resulted in the unit leaking inside the house. It was "fixed", developed a leak again, was "fixed", developed another leak. A new technician came & reinstalled the entire unit & it worked great - until it started leaking again...this time the issue was that the line out was too long & got stuck in mud & the water built back up into the unit & leaked again in the house. The same technician who re-installed everything came to fix it again & it's worked great...until this morning...we are now in heat mode & have been in heat mode for over a month - but today the wall was wet again....I checked to see if the line was backed up or anything like that - but don't see anything. I recently changed the filters - is there anything in my filter changing that would cause water to appear on the walls? Has anyone experienced water on the walls when their unit was in heat mode? thanks in advance

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Frank Carroll

about 4 months ago

My Daikin mini split will not heat. The cooling seems to work fine, but when I shift the mode to heat, the outside unit stops running and the inside fan doesn't blow. The louvres continue to swing, but no heat.

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Mitchell Anderson

about 3 months ago

Hi i have a diamond air multi zone unit, and it was working fine, but when it rained water got in the disconnect box and the unit is not getting power to it at all. I changed the disconnect box and there is still no power to the unit. Its getting power to the disconnect box but no power to the unit. Please can u help me?

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Mickey Luongo

about 3 months ago

The water probably shorted out the board.

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Jolene Scott

about 3 months ago

Hi We have a 2 year old Fujitsu Halcyon mini split running a ceiling cartridge downstairs and two smaller wall units in the upstairs bedrooms. A few weeks ago I came home to a cold house. The breakers for the unit were tripped. I reset them and still no power even to the thermostat. HVAC installer (via phone call with Fujitsu service techs) diagnosed fried circuit board, also the outdoor fuse was fried, Three new boards installed. This got power to the units, but fan speed was very weak at highest setting barely noticeable that air was coming out at all, the unit was set to the swing function but that function never engages, and air never warmed up with the thermostat set to 88 degrees, HVAC installer back, drained and weighed refrigerant (it was a couple lbs low). They pressurized the system but could not find a leak. Replaced refrigerant and asked that we leave system on overnight in hopes it would throw a code, Today HVAC installer back. The breakers were tripped again as well as the fuse blown. After replacing fuse and resetting breakers the compressor is now toast too. No error codes, ever. The service techs are really not very nice either. Of course, the warranty does not cover labor, so the HVAC installer is not happy to be spending so many hours (16 or so now) diagnosing over the phone with Fujitsu. No offer to have a Fujitsu certified tech come to see what's going on. This is way over the abilities of the HVAC contractor. There is no indication that there was ever any type of power surge. What can it be? I think we need a whole new outside unit.

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Jim Butler

about 3 months ago

I have a AUX mini split unit that heats fine but then the set temperature light starts flashing & the unit stops working. I can unplug the unit & replug it & it starts heating for a while & the same thing starts again Whats causing this to happen?

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Bethany

about 2 months ago

There is a dripping sound that our mini split makes. I know when it’s cooling or heating, this is normal. There is no leak or anything. Just curious if there is a way to muffle the drip sound... Is it possible to put a rag or towel there where it drips to muffle it or would that create more problem than its worth? Suggestions?

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Matt

about 2 months ago

Hi We have a few month old 9000 BTU Comfort Aire unit installed in our bedroom. Our contractor moved the location of the outdoor unit after it was installed and caused an issue with the refrigerant which then had to be refilled. After that the unit functioned correctly again for the last month up until the last few days. Now, nothing happens when we turn on the heat. When I turn on the AC, cool air does come out but I am unsure if that's just the cool air from outside or if the unit is actually working. Any thoughts on what might be the issue?

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Mickey Luongo

about 2 months ago

Sounds like a slow refrigerant leak. I would have the installer check the system again and verify all connections.

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Anton Koprivnik

about 2 months ago

My pioneer 24,000 ducted mini split is up and running. We are in the middle of winter and the unit is heating well but does not seem to be controlling the tempeture. Thermostat is set at 62 but the unit will heat up to 74 room temp. Running on auto mode and heat mode. Same results. Remote unit temp selected matches inside manual unit. Is this a thermostat problem or inside unit control board failure? There are no error codes.

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Mickey Luongo

about 2 months ago

Sounds like an issue with the thermistor in the unit.

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Bruce

about 2 months ago

I have a lg mini split system with three different zones. The two 9000 btu Units work fine but the 24000 btu unit does not heat the way it should. It runs fine for about 10 minutes then goes into preheat mode for 10 minutes and runs fine again. No matter what the thermostat is set at it Always goes into preheat mode 4 degrees before it reaches set temp. Is my problem with the thermostat or the unit itself . If unit is set on jet mode it runs perfect for the 30 minute set time. Any info will help as repair techs cannot figure it out .

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Wanson Hemphill

about 1 month ago

Hi: My Fujitsu heat pump is working good except the door won't rise up. I cleaned the screens and the cogs look fine. How do you set the cogs on the door before closing?

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Steve

about 1 month ago

Hi Mickey Just install ypthe Pioneer mini split. Model WYS012AMFI17RL. Instal went well no issues. However when I went to test and try the system the indoor unit doesnt work. I checked power from the fuse box to the line. Getting power. I checked power to the outdoor unit, yes getting power. I checke power at the indoor unit and no power. All the wires are tight and the red, black and white wires (1,2,3) are connsected to the same on the outdoor unit. I checked the wires directly at the indoor unit and not getipting power. What am I missing? Steve

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Gordon

about 4 weeks ago

I have a 18000 Panasonic mini split installed about a month ago that I cannot control the temperature on. Set to 20 and it will run until 25 and cut out. Set to 21 it runs to like 26 and cut out. Installer says this is normal and how the unit works but don't make sense to me. Any ideas?

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