Split system air conditioner (C) Daniel FriedmanMini Split A/C & Heat Pump FAQs
Diagnostic questions & answers set #2

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Mini Split-system air conditioner & heat pump Q&A set #2,

These additional questions & answers from readers help diagnose problems with split system or ductless air conditioner and heat pump systems.

This article series describes split system air conditioning & heat pump systems. We review the major system components, switches & controls, and typical applications for split system cooling systems.

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Split System Air Conditioner & Heat Pump System Diagnostic FAQs

A split system or "ductless" air conditioning (or A/C & heat pump) system dispenses with duct work entirely, using a wall-mounted indoor evaporator/blower unit and a separate outside compressor/condenser.

These split system A/C install, troubleshoot, repair FAQs were posted originally at SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS - home

On 2017-07-28 by (mod) - decode the flashing lights on a Sanyo Split System Air Conditioner


The flashing light on your Sanyo units might be normal: the light color and flash number can indicate an operating mode - model dependent. Other blinking lights can indicate "trouble in the system" according to Sanyo who then says "contact the service center"

Try running your unit's control through different modes to watch the lights on the indoor wall-mounted unit while you look at
cooling mode, timer on, quiet mode, normal cooling.

There are four lights or "lamps" on most Sanyo split system indoor units

Split System A/C Operation Lamp Colors

Those above are NORMAL OPERATING lamps on many Sanyo units.

Split System A/C Error Codes & LED Colors in the Outdoor Condenser Unit

Other Sanyo models such as the R−410A Ductless Split System: DLF4(A/H), DLC4(A/H) have LEDs giving operating status on the outdoor unit including (this is not the whole list)

Malfunction: here I'm only describing the yellow LED flash codes:

Yellow LED Malfunction Flash Codes

Those may help you out but you can read from this that what is really needed is the model number and then a consult with its operating and troubleshooting manual.

We provide links to some Sanyo equipment at SANYO Air Conditioners, Heat Pumps, Split Systems, Inverters

On 2017-07-28 by Ken Mc

I have a Sanyo mini split system with 2 head units, one upstairs and one downstairs. The units run normally for about one to two weeks, then the light on each head unit continues to flash.

The fans still run, but it seems the compressor stops running/ cooling. I shut of the main power breaker to the unit for about 5 or 10 minutes, then turn it back on. The system seems to reset itself and will run normally again for another week or two, then the same thing happens again! I have no problem maintaining temp when it's running normal.

I've changed batteries and reset the remotes, which have a clear line of sight to the head units. Any ideas as to what is causing this issue?? Thanks!

On 2017-06-21 by Joanna

I have split unit in pen on the bottom i see stending water and air conditioner stop I collect water and then start running
Way I have water in pan what I should do
To fix this

On 2017-06-16 by Mike

My Mitsubishi ductless system is low on refrigerant and was installed in 2011
Do I need to have a costly leak check or should I just have freon replaced, it is at 40%.
Is it normal to have freon level go down after 6 years?

On 2017-06-12 by (mod) Compressor unit fan runs continuously


Some systems have a "fan-on" control switch on the remote or right on the bottom of the indoor air blower unit itself. Check that those are not set to ON or MAN.

When the A/C is OFF and the fan is running you are continuing to circulate and filter the air, but that should not be the cause of an odor;

Take a further look at the air conditioner wall mounted indoor unit to see if it looks moldy - Then see SPLIT SYSTEM AC MOLD CONTAMINATION REMOVAL at

It is normal for indoor humidity to creep up in hot humid weather when the A/C is "off" - the fan won't be the cause.

Some split systems like our office Sanyo unit have a "dehumidification" mode that is specifically designed to reduce indoor humidity without making it too chilly indoors. What underlies this problem is this : if an air conditioner is over-sized (too much BTUh cooling capacity) for the space it is conditioning, it will drop the indoor temperature too quickly - before dehumidification has been sufficient.

That's because the system needs to run longer -not just the fan but the cooling system - to remove high levels of indoor humidity.

Keep me posted.

On 2017-06-12 by Not so pleased

When our split unit air conditioners are on, the fan runs continuously even when the compressor turns itself off. When the compressor turns off (but the fan is still running), the room begins to feel very humid and it has a horrible, musty smell. All of our units have had the same issue since day 1. There's not an option to have the fan shut off when the compressor stops. Is this smell and humidity normal? Is there anything I can do about it? It bothers me immensely. Thanks!

On 2017-05-22 by (mod) bad reversing valve on heat pump


I agree that a reversing valve that's not working properly or is cycling could cause loss of cooling, but it seems more likely that your system has a refrigerant leak.

On 2017-05-22 0 by Rajun Kajun Lennox heat pump Mod:12hpb with a CB30M air handler.

I have a Lennox heat pump Mod:12hpb with a CB30M air handler. The unit runs constantly but little to no cooling .

Defrost reversing valve seams to shift from A/C to Heat mode, checked the temp at the Liquid and Vapor lines & Liquid line is 84*F and the Vapor line is 81* F ambient temp 94*F.

I can not determine if the defrost reversing valve is leaking and would be the culprit.The Defrost Control Board Led's both are on constant red. I Am a 36 yrs veteran in A/C-H, Commercial refrigeration & electrical business and am retired now.

Could use much needed assistance ASAP. w r i t e me-r a y m on dflo ry @ g m ai l,c o m wife dealing with cancer 10 yrs.
Thank You very much......

On 2017-02-11 18 by (mod) fujitsu split model asta12lccm error codes


The installation/operation manual for your Fujitsu ASTA121CC air conditioner will give the error codes and their meanings. However in the Fujitsu catalog I could not find this model number.

The Fujitsu AST series air conditioners that I could find use the name ASTGnn... Can you check the model number and upate us or confirm it?

See FUJITSU Room Air Conditioners for free down-loads of manuals as PDF files

On 2017-02-11 by danny skoglie

i have a fujitsu split model asta12lcc that has the operations and timer lights flash 3 times together and then the operations light flashes twice by itself.

On 2016-12-17 by Greg

I have a LG mini split 1200 BTU
It was working great on cooling past summer but now winter has arrived it's set to heat
We can get heat but a very low flow of air even when remote is set high

It seems that we can set remote at any high Temps but always only works until 17C then shuts off
I cleaned filters and check compresser and seems all OK
Could this be a bad control board or hopi g a simple fix

On 2016-12-03 by Richard Robinson Senville Aura 18HF/MO

Greetings. Senville Aura 18HF/MO installed in July 2014. Dual head. Worked fine until one of the heads quit blowing hot air, really does not blow at all.

The other head is still functioning fine. When I turn on the malfunctioning head, the fan in the outside unit turns, after approximately 5-10 minutes the outside unit will make a whosing sound like air brakes, but deeper.

Any suggestions before I call for service? Thanks

On 2016-11-18 by Mavis Kemnitz Trance spot unit system

I have a trance spot unit system. In the heating mode the temp display switched to HI. What does that indicate?

On 2016-11-14 by Gwen Sullivan Sanyo KHS 1872 split system AC

Have a Sanyo KHS 1872 split system AC. About 4 years old and starts/runs fine except for high pitched, steady humming when running in HEAT mode only. Does not hum when in AC mode. Humming is from inside unit. Have cleaned filters. Do you know what the cause might be? Thanking you so much in advance.

On 2016-11-13 by Cindy Knotts

I have a Lennox split ductless 24000 but. I have 2 12000 btu units inside. One in the living room and one in the bedroom. I cannot run them both at the same time. One comes on and the other one will not. Do you know why?

On 2016-11-11 by jeanpierre Directair heat pump MSAEB-12HRFN1-MT0W

hi, I have a Directair heat pump MSAEB-12HRFN1-MT0W, 20 SEER, 12k Btu/H. one of the indoor units is acting strange, the system is only 3 months old,

the problem is when I power up the head unit it comes on and after a few moments it shuts off and displays -- in the temp indication window. is there something I can do or do I have to contact the installer. can you explain what is happening please.

On 2016-10-31 by (mod) 1 pipe is icing up on split system AC

Dunno, Colin, from just the brief question; could be a clogged expansion valve or low refrigerant or something else I've not thought-of

On 2016-10-30 by Colin

Have a split unit. When running, 1 pipe is icing up and there is no heat on the other pipe. But air does not cool.

On 2016-10-21 by (mod) - can't shut the split system down with the remote

Sounds like

- improper switch setting on the wall unit - manual-on mode
- dead batteries in the remote
- something else we've not thought-of

On 2016-10-21 by Rudy

I have just installed a min split unit in my house

When I set the breaker the out side unit turns on by itself. The inside unit start to cool but I can't shut the unit down with remote only if the breaker is tripped.

On 2016-08-15 by (mod) condensate leaks on split system AC


The split units I've worked with used individual condensate lines from each indoor air handler to the outdoors. It sounds to me as if your system condensate lines need to be investigated.

Also check for a wall-mount that's not level on the wall; condensate may not make it to the tray drain opening.

On 2016-08-15 by Harvey N

We have a new split unit--with a 12 and a 7 outlet. When one unit is in off mode and the other in Cool mode, the Off Unit begins to accumulate condensation and then to leak water.

Must both units always be in the same mode, or can one be turned off?

On 2016-07-20 by (mod) chemical burning smell from Fujitsu Halcyon I.A.Q. unit


KEEP TURNED OFF ELECTRICAL POWER to the system. It sounds as if there is a failing control; there is a risk of an electrical fire.

On 2016-07-20 by Pam Grant

When I turn on my Fujitsu Halcyon I.A.Q. unit to cool down out of the blue and quickly it emits a very strong chemical burning smell, as if something is on fire inside the unit.

Has anyone come across this before? We had to turn the unit off and leave it off.

On 2016-06-15 by (mod) ok to install indoor half of a split system AC on an interior wall

You can certainly install a split system indoor half on an interior wall, we've done that; the refrigerant line has to be appropriately routed and you might need to increase the charge according to added volume for the piping length.

Refrigerant lines can run in any direction; However some components like some TEVs must of course be in an "upright" position as the manufacturer may specify.

Watch those flexible condensate drains - I've found sags and as a result clogs and subsequent blockages if the lines are not run with care, sloped and supported. We want standard drain slope of 1/8 to 1/4 " per foot.

On 2016-06-15 by Matt

I have a Mrcool 36k btu DIY pre-charged unit that I'm currently in the process of installing. The room I'm installing it in isn't on an exterior wall unfortunately.

I want to install it through the indoor wall, then run the refrigerant lines up vertically about a 1.5' to the ceiling, then strait across the ceiling, then out of the exterior wall, and down to the outdoor unit. Is it ok to run the refrigerant lines upwards like this? I have the condensate drain separate and angled with a downward flow.

On 2016-06-01 by (mod) heat pump needs service

You really system need service, perhaps a refrigerant leak or a bad expansion valve. Unfortunately, No one can diagnose your system from your e-text.

On 2016-05-31 by James d

Can someone help me

Have a heat pump two zone run great when both fan are blowing but when turn off fan downstairs lined start to ice up and compressor kicks off font know why

On 2016-04-30 by Adam

I have a Pioneer mini split heat /ac system. According works, fan works, but when I put in heat mode it goes into defrost /run mode and does nothing. My manual says it should take 4-10 minutes and then work but it doesn't. It's a brand new unit, installed today. Can anyone help?

On 2016-04-26 by Hamed

what is the type of the oil using in unionaire air conditioner compressor?

On 2016-03-10 by Anonymous - Mitsubishi split unit

Mitsubishi split units power on and run for 5 minutes then green LED light blinks and air stops blowing. Vents continue moving but no air coming out.

On 2016-03-06 by (mod) clicking noise but split system won't start

I'd leave the system off as it sounds as if a motor was unable to start. Keeping power off while waiting for repair reduces the chance of other damage.

On 2016-03-06 by betty

i shut down the system whn i heard the clicking and i guess it kicked the breaker. i haven't restarted it or flipped the breaker back yet

On 2016-03-05 by ken lentz - a Mitsubishi 4 ton mini split and the outdoor unit is icing up

Can you suggest what one might do to troubleshoot the following problem. I have a Mitsubishi 4 ton mini split and the outdoor unit is icing up at the accumulator. I carefully measured the added refrigerant so.... Anyway it is the accumulator icing up not the compressor.

On 2016-02-13 by (mod) - charge a Mitsubishi Mini Split and heat pump mode under 30 degrees?

Yes with proper charging measurement and monitoring equipment.

On 2016-02-13 by scott

does anyone know if I can charge a Mitsubishi Mini Split and heat pump mode under 30 degrees

On 2015-12-19 by (mod) - heat not working on mini split in heat mode

Backup heat may not be working

On 2015-12-18 by andres

I have a mini split system heat pump and when I switch to heat the condenser comes on and the air handler it won't come on

On 2015-12-16 by (mod) which lines are hot and cold on a Pioneer mini split?


In normal A/C and heat pump operation one line is warm to hot - depending on where along its length you check its temperature - and the other cool to cold.

The suction line or low pressure line is cold and the high pressure line or refrigerant line can be hot - depending as I say on where it's touched.

On 2015-12-15 by Michael G.

I have a pioneer mini split unit and one line is hot and the other is cold.

On 2015-12-02 by (mod) - error codes & error lights n HVAC mini split systems


Error codes on HVAC equipment are not set to an industry standard. To know what "F0" means one would need to

1. identify the brand of your A/C or heat pump equipment
2. Get the model number from the equipment data plate
3. With #1 and #2, obtain the installation and maintenance manual or owners' guide for the equipment.

There in we'll pretty much always find a table of error codes, what they mean, what to do about it.

I can offer thus only a very general opinion from your note:

it sounds as if there is either a refrigerant loss or a refirgerant metering device failure.

This is not likely to be something that a homeowner can repair; rather you'd need to call your HVAC service technician.

On 2015-12-02 by Ed - Error code F0 System charge shortage or blockage protection

Error code F0 System charge shortage or blockage protection (Indoor room temperature failure) What causes this code? How do I repair it?

On 2015-11-26 by (mod) - only half of dual heat pump working


Shortening a refrigerant line won't cause a heat pump to stop working, but failing to install a proper charge, filter/drier, or a control relay could be the trouble. IF the motor doesn't start at all then it's an electrical or control problem.

On 2015-11-26 by chris leblanc

I just had a dual zone heat pump installed one head is working fine the other wont work in auto or heat mode I noticed the installer cut about 8 ft off one of the 16 ft lines any ideas

On 2015-11-21 by (mod) - diagnose Mishubishi Split-System Heat Pump Model PKA-A12HA4 (air handler) Model PUY-A12NHA4 (Condensing unit)


If it's quite cold out then your system may be switched to backup-heat and it'd be the backup heat that's not working.

Otherwise, presuming the thermostat is correctly set, I suspect a bad temperature sensor or control board.

On 2015-11-21 by Tom N

I have a Mishubishi Split-System Heat Pump Model PKA-A12HA4 (air handler) Model PUY-A12NHA4 (Condensing unit) . In the summer time the AC working great. Now i switch to Heat Mode. But only cold air coming out. Please help

On 2015-11-20 by Byron E - Samsung split unit blower doesn't work

When I select the heat on My Samsung split unit...the heat pump runs but the inside blower doesn't come on even afetr waiting 10 minutes.. The inside blower does work when using other settings. What should I check??

On 2015-11-18 by (mod) - LG split ductless timer programming

Tim, the brains are usually in the remote in this case. Check the position of the slide switches inside the remote cover. One may need to be set to AUTO.

On 2015-11-17 by Tim

Our l g split ductless has a timer on and off program so I set it up to come on at a certain time and also to turn off at a certain time.I have it in the heat mode by the way.

Anyway it doesnt come on at the selected time. Otherwise it works fine.I am wondering if I should have programmed it with the remote pointed at the wall unit?

On 2015-11-02 by (mod) - ductless split air conditioner not getting cold

Well it ought to be doing one or the other - so "everything is working" doesn't quite sound right.

If the outside compressor runs and the inside unit blows air but doesn't cool in cooling mode (or if it's a heat pump model and also doesn't heat in heating mode) I figure either someone forgot to install the refrigerant or there is a bad control board or module.

Be sure you're in cooling mode and that the thermostat is set well below room temp.

On 2015-11-01 by Mr. Custis

The ductless split Air conditioner/heat pump has been installed everything is working but it's not getting cold and its not pumping out any heat.

On 2015-08-06 by (mod) mini split won't blow warm air


If your mini split is an air conditioning system only, that is not a heat pump, then it should not be blowing warm air, just cool air.

If it's a heat pump then a control or reversing valve is stuck or broken.

On 2015-08-05 by Tim

Our ductless mini split was working just fine but we didn't use it for maybe 9 months or so. Now the air conditioner works fine but the unit will not blow any warm air. Help please.

On 2015-07-17 by (mod) Frigidaire split type air conditioner doesn't respond to remote


The remote control typically has a cover you can open to set programmable themostatic controls for the split system AC unit. Just remember to leave the remote where the wall unit can "see" it.

On 2015-07-13 by Melanie O

I have a Frigidaire split type air conditioner. I want to be able to set high/low temps so that the unit will turn off/on automatically and maintain a certain temp range.

It seems like there is no option for this, that I have to manually switch it on and just let it run until I manually switch it off. This doesn't appear to be very energy efficient, especially at night. I've read the instruction manual and can't seem to figure this out. Any advice?

On 2015-07-10 by (mod) Mitsubishi Mxz3B30NA Outdoor Unit with 3 Msz-Geo9NA Indoor Unit - sizing vs dehumifification

I would first check the air flow temperatures to see what actually happens with cooling; then same with indoor relative humidity at the unit and in the room center;

I'd check the cool-down time. If the room cools off too fast then in general an AC system won't dehumidify. For AC systems that have a dehumidification mode you're basically trying to remove humidity without continuing to cool down the room - I'd make the same measurements with the equipment in that mode.

Then I'd go to the manufacturer with that data.

keep in mind that advice about HVAC sizing, to be accurate, needs to consider more than room size; we add consideration of the building heat gain rate and we also look for sources of moisture beyond normal, such as leaks or wet crawl areas.

On 2015-07-10 by Eddie

In June 2014, I installed a Mitsubishi Mxz3B30NA Outdoor Unit with 3 Msz-Geo9NA Indoor Unit. Installed in Bedrooms that are about 12 X 12 ea. Mitsubishi said that with Hyper system this would work. fine. They would only give enough cooling for 0 to 400 sq ft. what every was needed for the room. They encouraged me to put this size in.

Now the room will cool and take the humidity down some. Then the humidity will go as high as 80%. Plus this unit has a dry mode that's supposed to take humidity down instead it will increase. What do I do now

On 2015-07-07 by Chris

How do your clean the outdoor unit of a split system air conditioner (Sanyo KS1872)

Question: it looks as if smoke or steam is coming out of our wall-mounted split system air conditioner/heat pump

We saw smoke or maybe it was steam (since it didn't smell) coming out of our wall-mounted split system air conditioner/heat pump - is this dangerous? - Anon.


Fujitsu has pointed out that at least on their mini split system heat pump/air conditioner wall mounted units a white steam coming from the air handler indoors may be perfectly normal. [9]


(Sept 5, 2012) Pearl said:

Why the air cond wouldn't work because the wall-mounted AC LED'S keep blinking from RUN to TIMER.


Perl, check your remote control settings; if the remote has been accidentally set to put the A/C in timer mode, it may not be turning on and off manually.


(Sept 22, 2012) roy said:

I have a firstline split airconditioner mod no.fcs 12000ch.. I wish to move it to another area of my home.
First can you tell me where I can get a instruction/maintainence manual. I would like to know if this model
can service two wall mount outlets. Thank You Roy



take a look at the outdoor compressor / condenser unti. If yours can handle more than one indoor air handler there will be more than one refrigerant piping hookup connections.

You can obtain a service and installation for Firstine split system air conditioners from

Selecrairecon [dot] com, telephone 64 717 1531 Or 96 671 or 9362


(Oct 4, 2012) jankarl said:

i accidentally touch the heater button on the remote control of lg split type airconditioner but i change right away the setting to colling but it doesnt work hot air still coming out.



Try turning off all power to the equipment for 30 minutes, then back on.


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