Guide to ductless split-system air conditioners: This article describes split system air conditioning & heat pump systems. We review the major system components, switches & controls, and typical applications for split system cooling systems.
We also discuss use of the remote thermostat control, where to find and how to clean the split system air filters, how condensate is disposed-of, and what to check first if your split system air conditioner is not working properly.
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Split System Air Conditioner & Heat Pump Systems: controls, operation, diagnosis, repair & component parts guide
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 (below left and right). In this split system air conditioning design, one compressor/condenser may serve multiple wall-mount indoor units.
The ductless or split and mini-split system air conditioners used in our illustrations are Sanyo brand, but there are quite a few split system and split system mini air conditioners currently on the market, including models by Carrier, Friedrich, Frigidaire, Goodman, LG, Mitsubishi, Panasonic, Sanyo, and Samsung.
The basic components, installation, and maintenance procedures here apply to all types of mini split system or ductless A/C and heat pump units, but of course you should also read the manufacturer's installation and users' guide for your unit as well.
Split system air conditioners and heat pumps may use a remote control device to turn the equipment on or off and to set the desired temperature. You will also find some operating switches and controls on the indoor wall-mounted cooling unit air handler, for most split system cooling units and heat pumps, the user is expected to use the remote control.
Remote control thermostats such as the unit shown at left are usually used with air conditioning or heating split systems using an outside compressor/condenser unit and one or more indoor wall-mounted cooling or heating units..
The thermostat controls in the hand-held remote control communicates with a wall-mounted air conditioner or heater using infra red signals. The open finned area at the bottom of the remote A/C control (at the left in our photo) permit ambient air to enter the control for purpose of sensing the air temperature.
A control such as this Sanyo (TM) unit can be quite sophisticated and include automatic set back temperatures, timers, etc.
On the remote control for a split system A/C or heat pump unit there are typically two levels of operating controls or settings.
Also see THERMOSTATS.
And at A/C - HEAT PUMP CONTROLS & SWITCHES we describe all of the controls and switches found on residential and most commercial air conditioning and heat pump systems. Other controls that affect a split system air conditioner or heat pump will include
You can see the outdoor service switch (circled in red) in our photo at left. Depending on the installation, this box may contain fuses, a circuit breaker, or a simple pull-out that can kill power to the unit.
If your split system A/C unit is not cooling, remember to check this switch to be sure that power is being delivered to the unit.
Watch out: at installations using aluminum wire to bring power to the outside compressor/condenser unit the electrical connections between the aluminum wire and the lugs inside the service switch can fail, leading to overheating, loss of cooling, repeated cooling outages, and even an electrical fire. Extra care in making aluminum wire connections such as using an approved antioxidant and proper connection torquing significantly reduce this hazard. Details are
(May 8, 2014) Barbara said: I need to replace (2) remote controls for my A/C units. The model # is RCSKS09. I can't seem to find them anywhere. Any suggestions, would be appreciated.
(July 3, 2014) Karen said: I am alsolooking for a RCS-KS09 remote for AC Unit KMS 0912 and cannot locate one.
Reply: How to fix or replace a remote control thermostat control for an air conditioners or heat pump
A remote control air conditioner thermostat (like the one in our photo) control communicates with a wall-mounted air conditioner or heater using infra red signals. The open finned area at the bottom of this Sanyo control (at the left in our photo) permits ambient air to enter the control for purpose of sensing the air temperature.
Several manufacturers sell a generic remote control that works across their product line.
Barbara replies: Sanyo Model # RCSKSO9 - thanks
Barbara, at the following address Sanyo offers the remote control you need
A control such as this Sanyo™ unit can be quite sophisticated and include automatic set back temperatures, timers, etc. About how to diagnose and fix an air conditioner remote control unit:
(May 8, 2014) Barbara said:
Thank you so much for the link, but I can't find my Model # when I go to the link.
Barbara, Sanyo says their remote works with all of their equipment. If that's not satisfactory for you then your next step is to contact the company either at
Replacing the hand-held remote control for an A/C system:
If you mean that you need to replace the hand-held portable remote control for your air conditioner, a new unit is best bought from the manufacturer themselves as that assures complete compatability with all of your air conditioners features.
How to troubleshoot & fix an air conditioner or heat pump remote control
If you mean that you think the remote control problem is inside of the wall-mounted A/C of a split system air conditioner or heat pump then I have some different advice. Basically, since the problem is usually in the hand held control unit, start there with these diagnostic and maintenance tips:
Check the remote control batteries: Start with replacing the remote control's batteries, then turning it back on and testing it's ability to control the A/C unit.
Watch out: a simple mistake like putting the batteries into the remote control with the (+) and (-) ends pointing the wrong way is enough to keep the control from working.
Check the air sensor port on the remote control and the control resting location: if the remote control seems to communicate with the wall unit but temperature response is not what you want, check that the openings that allow room air to enter the remote control are not blocked with dust or debris. Also consider where you are leaving the remote control. If you place the control directly in the cool air path of the A/C unit it will be "satisfied" sooner than you may wish. If you place the remote control too far away, out of the room, or in a dead air space or under a magazine, clearly it's not going to be able to respond well to the actual room temperature.
Also see THERMOSTATS, HEATING / COOLING.
Split System Air Conditioner Air Filter Maintenance - How to Clean a Split System Air Conditioner Filter
Wall-mounted split system air conditioners as well as window air conditioner units include one or more removable air filters that are designed to be simply rinsed clean using cold water.
You can wash these plastic mesh filters in the kitchen sink using a dish sprayer but I prefer to perform the operation outdoors (shown below). Outside avoids messing up the kitchen and eliminates any risk of drain clogs.
Watch out: We have read of washable air filters that can be sent through your dishwasher. We do not recommend this step - as you risk clogging the dishwasher or its pump with dust and debris that wash off of the air filter.
We took two photos (shown below) of a pair of washable air filters pulled from the indoor cooling unit of a wall mounted split-system air conditioner used in our lab.
Holding up the two washable air filters and trying to peer through them, even in the dim afternoon light, that the clean filter (on the right) is almost transparent, while the dirty air filter (at left in our photo) is completely opaque.
This simple visual test can confirm the state of a washable air filter.
Watch out: these washable filters are pretty tough, but we offer these additional care recommendations:
Take care not to tear or damage the filter screen. Torn, the air filter will allow dust and debris to accumulate in the cooling system - leading to reduced cooling, frost or ice formation, and eventually the cost of a professional cleanup job.
The plastic filter is much thinner than the larger pleated paper or fiberglass filters used in the air handler of central air conditioning systems or heating furnaces. That means the filter should be inspected and cleaned with diligence - monthly during a season of daily use would be smart.
Additional ultrafine particulate filters on some Split System A/C and Heat Pump Units
Some split system air handlers include an extra internal filter intended to reduce ultrafine particulates such as from tobacco smoke. These filters are optional and might slightly reduce the air output from the unit. Fujitsu advises as follows:
Watch out: if you take a look at this filter you'll see it looks like fragile cardboard - it is not washable but rather is a disposable filter that is replaced as needed.
Some split system air handlers also include a negative ion generation feature also intended to remove some odors and ultra fine particulates from the air flow. Quoting:
The negative ions system includes an internal filter sheet that should be replaced every few years. (Say 3 year intervals). 
Proper slope is important for split system in-wall condensate drains
Our photo (left) shows a white flexible tube used as condensate drain tubing for a split system air conditioning system being installed in a New York Home. (click photo to see an enlarged, detailed version). Photo courtesy Galow Homes.
Even now the drain is not perfectly sloped (note it's a bit high at that second cripple stud from left) but it was much worse before we re-routed the drain. The air conditioner installer had the drain line sloping up-hill in the area I've circled in the photo.
Having already had condensate drain line clogs and backups and leaks from the indoor air handler into the building wall at another split-system air conditioner where the condensate drain was improperly sloped and clog-prone, I was not going to let it happen again at this installation.
The installer thought I was being unreasonably demanding. But then, he was ignoring the plumbing code (1/8" per foot slope for condensate drain lines) and apparently didn't recognize the potential costs in rot, insect damage or mold if we simply let the condensate drain clog (due to an improper slope and dust that will enter the line) followed by leaks into the building wall up at the air handler.
The condensate drain line and refrigerant tubing (black-insulated in the photo) were installed and the wall was prepared for blown-in insulation. Once the wall was insulated and drywall was installed, repairing an improperly-sloped drain line would have been much more costly and disruptive.
You'll see that we also installed nail plates (Nail Stops) to protect the condensate drain and refrigerant tubing from being punctured by screws or nails to be used when the drywall was installed.
A closeup of Simpson Strong-Tie's NS2 6-inch nail stop (Protecting Shield Plate Nail Stoppers) is shown at left.
We use nail stops to protect electrical wiring as well as plumbing piping from nail or screw punctures. 
Our photo at left shows the termination of the condensate drain line for this spit system air conditioner.
The white plastic flexible tubing ran through the building wall, was tied to the refrigerant lines behind the Sanyo inverter unit (compressor condenser unit) and then allowed to fall freely onto the rubber roof where condensate drains off the roof and into a gutter and downspout system for final disposal.
Since this system is a cooling-only unit, it does not operate in winter and we were thus not worried about the risk of freeze-up of the condensate disposal drain line.
At Installing Insulation on Air Conditioning & Heat Pump Refrigeration Lines we describe how insulation should be installed on the refrigeration lines both inside the building (and in building walls or other cavities) and outside at the compressor/condenser or A/C inverter unit.
For A/C compressor/condenser (inverter) outdoor units that are mounted above ground on the building wall, also
Avoid gaps and missing insulation along the refrigeration lines
Proper placement and securing of insulation on air conditioner or heat pump refrigeration lines is important to avoid condensation leaks into the building. One, or on some systems both refrigeration lines can be cool or cold under some operating conditions.
The cold copper tubing in contact with warm humid air causes moisture in the air to condense onto and then drip off of the refrigeration lines.
The result can be leaks into the building, as our photo at left illustrates. The drip stains on the attic floor may well indicate a point at which leak stains or even mold appear on the ceiling below.
Our photograph illustrates the importance of not compressing refrigeration. In our photo at below left, see the drip stains below the condensate lines at each location where the insulation was compressed by a too-tight plastic tie.
That same accumulation of water in a wall or ceiling inside which the dew point may be reached on the refrigeration lines is asking for a costly mold, insect, or rot damage problem later on.
Missing insulation on the refrigeration lines outdoors is not a catastrophe - at least for a short un such as at this split system compressor/condenser unit. Perhaps a little loss in efficiency of the system operation in some weather conditions.
On a long refrigeration line run, say between an attic air handler and a ground level compressor/condenser, the effects may be more significant.
Details about refrigeration piping insulation are provided
Watch out: The same split system air conditioner installer we described above
During the first season of use of the newly-installed Sanyo split system air conditioner the building occupants noticed water stains and rippled wall paint extending down the wall below the indoor air handler cooling unit.
Our photo (left) shows where the refrigerant lines rise in the wall to enter the wall-mounted half of the split system air conditioner (that larger white area below the left end of the unit) and the blue tape marks where we first saw condensate water dripping from the unit.
We found that there was no insulation whatsoever on the refrigeration lines that ran horizontally along the rear bottom of the unit. The result was condensation on the refrigeration lines that did not drip into the unit's condensate tray but rather fell into the plastic bottom where water leaked out onto and into
The "fix" for this condensate leak was the installation of foam insulation along the refrigerant lines inside the unit, from their point of exit from the building interior wall surface to their point of connection to the cooling coil.
Details about how we found and fixed this condensate leak from the air handler are at at REFRIGERANT PIPING INSULATION.
Watch out: inadequately-supported outdoor window air conditioners or inadequately-supported wall-mounted outdoor compressor/condenser units (referred to as the "inverter unit" in some literature) pose a potentially fatal hazard should one of these units fall from the building onto someone below.
Details about the need to support window, through wall, or wall-mounted air conditioning & heat pump equipment are found
Fujitsu provides some helpful advice about troubleshooting weak air flow from the indoor wall-mounted component of a split system air conditioner or heat pump. The following are adapted from that source: 
Causes of no air flow or very very weak air flow from the A/C - heat pump unit
Causes of weak air flow from the wall-mounted split system A/C or heat pump
How to diagnose poor or inadequate cooling or heating from a split system air conditioner or heat pump
Convert a Split System Air Conditioner to a Heat Pump System?
Reader Question: 8/2/2014 Roy Brown said:
Is it possible and about how much would it cost to convert a sanyo single zone ks2472 system to a heat pump system?
Roy, the Sanyo system you cite, is described by its manufacturer and vendors as follows:
Sanyo 24KS72 24,200 BTU Single Zone Wall-Mounted Cool Only Ductless Split System with DC Inverter, Microprocessor Controls and Wireless Remote Control (KS2472/CSKS24NKU Indoor/ C2472/CUKS24NKU Outdoor)
This unit is designed to operate in 3 modes: Dry (dehumidifies), Cooling, and Fan (just circulates air); as it does not provide a heating mode, this is an air conditioner, not a heat pump.
Heat pumps add certain controls such as a reversing valve to reverse the direction of refrigerant flow, and indoor controls to swap from cooling to heating mode.
Most likely you'd need to replace the whole system rather than to try to retrofit parts and controls where they were not intended.
Sanyo does sell a very similar system to yours that IS a heat pump - thus capable of providing heating in cold weather, model
You can confirm this with Sanyo at:
Continuing for Roy- here you can see that both indoor and outdoor components of the Sanyo AC split system are different from the indoor and outdoor components of the Sanyo Heat Pump split system
So you see the components are different and are not matched - supporting my surmise that you'd need to replace the entire system.
Incidentally the Sanyo 24KLS72 is a discontinued model.
Current price quotes range for the Sanyo Split system heat pump KHS2472 range from about $1800 to $3500 U.S.
This website discusses these air conditioning and heat pump terms and problems: Air Conditioners: Central Air Conditioning Troubleshooting & Repair Guide: How to Inspect, Diagnose, & Repair Central Air Conditioning: Defects in A/C compressors, air handlers, duct work, and controls. We explain how to inspect & repair central air conditioning systems and for homeowners we also answer basic HVAC questions such as what are the basic air conditioning components? We provide guidance in determining air conditioning cooling capacity & energy efficiency, Troubleshooting air conditioning compressor problems, Diagnosing air conditioning air handler problems, Air conditioning condensate problems, Duct system inspections, defects, repairs, Cleaning air conditioning equipment & A/C refrigerants.
Continue reading at SEER RATINGS & OTHER DEFINITIONS or select a topic from the More Reading links shown below.
Suggested citation for this web page
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Frequently Asked Questions (FAQs)
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. 
(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.
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.
(Nov 20, 2012) Airkool guy said:
I am trying to replace the remote control of a Unionaire Split air conditioner with a Honeywell type of wall digital switch that controls fan speed and temperature. Iv managed to wire the fan and on off controls but I can't seem to get the compressor wiring correct. What is correct wiring procedure to follow?
Over at our THERMOSTATS HEATING AND COOLING article (link at page left) there are articles on wiring details. But also for the equipment you named, most likely there are detailed wiring instructions in the box. If not give me model numbers and I'll look further.
(Nov 28, 2012) Jade said:
I have a Samsung wall mount air conditioner, heating unti as well. Brand new and now when i try to put some heat on , it flashes red and green and beepes?? What does this mean and how can i fix it?
(Nov 29, 2012) Mizu said:
If you run a split system just as a fan without the AC cooling, does the unit still suck air into the fan/room from outside, and is this a more economical way to ventilate a room than to use a ceiling fan (I'm thinking of cool nights, when the ambient outside air temp is lower than that inside the room)? Thanks.
No, Mizu. The split systems discussed here do not typically obtain any outdoor air.
(Feb 18, 2013) Anonymous said:
i have a fujitsu heat pump...my outside fan will not start. error indicates fan motor error.is there a way to check this and is there a reset on the motor itself?
(Mar 12, 2013) robert said:
I have got an air conditioner labelled FIRSTLINE fsc 1200 the problem is that it is out of order, ingact when, I turn it on, 3 alerting lights all toghether remains on...what does it mean?
Robert, if you have the owners or installation manual for your air conditioner ithat document will decode the indicator lights. Codes indicate trivial things like "clean the filter" to conditions requiring actual repair. First check the obvious things listed in the article above.
If you don't have the a/c manual, tell us the model and serial numbers and we'll see if we can find it for you.
(Mar 27, 2013) Dennis G.Gabriel said:
Why is my Samsung ductless heat pump...outside unit...freezing up?
Could be low refrigerant, bad expansion valve, defective control, blocked coils. YOu need a service call by a professional.
(Feb 13, 2014) Nellie said:
Our split unit A/C works fine for half an hour. Then the outside fan picks up speed and becomes noisy. It shuts down and after several minutes starts up again, only to begin the cycle again. However at night the unit operates as it should be. It is not the compressor (replaced already).
Nellie, it sounds as if the outside compressor/condenser unit is in trouble; I can't tell from your note if the concern is just the fan or fan motor, or if it's a more costly problem like the compressor itself. But the fact that you say the system operates OK at night suggests that it's overheating, and having trouble working during warmer daytime hours. Some folks have tried diagnosing this overheating issue by spraying water up so that it falls as if rain onto the outside compressor condenser unit - cooling it down; in any event you need a service call.
(May 9, 2014) Rebecca said:
We own a BnB and one of our units is not working. The wall unit is lit and showing set to a/c with thermostat set on 80. The remote shows 74 and a/c. When you point the remote at the unit, it does not respond. Purchased new batteries - no change. The two are apparently not "reading" each other. I am sold out this weekend with guests, and I don't know what to try next! I flipped breakers on and off, I changed batteries in the remote twice. Normall there is a "beep" when the remote speaks to the unit, but there is nothing at this time. Suggestions would help - my HVAC tech is out of town on vacation!
Rebecca, if the A/C unit is working when you control it directly from the thermostat but not from the remote unit, then clearly it's a problem with the remote-TT communication. Try powering off both units and then back on.
(May 30, 2014) monte said:
please direct me, to finding an age for Mitsubishi split system. serial #0000577t
See the Age of Air Conditioners article at
(july 20, 2014) jesus la salle said:
I've got a code (e1) on my split air conditioner. Brand name is (comfort breeze) inverter 12000 btu. I turn it on, in the inside turns on but not the compressor. After a couple of minutes the (e1) turns on and everything turns off. What could it be?
7/31/14 Jeff said:
Our wintair split ac, seems to have trouble starting. Upon start up the outdoor unit fan runs, but for abour 10 sec... Then a loud humm, seems to cut the power to the fan, like a relay that cant seem to engage, or a motor that wont start. This repeats for about 10 times, and only then can you hear the compressor really engage. And then it seems fine.....for now. Any ideas.
It sounds as if the compressor is unable to start - a bad compressor motor or a failed start capacitor.
Dan, thanks for your reply, how to pinpoint the problem? I am pretty handy but dont have much experience with ac. I assume to replace any of these components, i dont need to mess with the refridgerants. Or would you recommend a pro to repair this?
Jeff, If the compressor is failing it's not a repair a typical homeowner would nor should undertake. Cutting, cleaning, soldering refrigerant lines, pulling a vacuum, installing new compressor, installing special burnout filter driers, and even before that, proper diagnosis of the problem are in order.
(Aug 4, 2014) Wayne said:
My minisplit AC turns itself on and off at will intermittently, but otherwise works very well for days. any suggestions
Check out the diagnostics at inspectapedia.com/aircond/AC_Compressor_Hard_Start.htm where we discuss intermittent AC operation under the aegis of hard-starting compressors.
Question: Tripping breakers on AC systems
(Aug 17, 2014) Anonymous said:
the united was running good,buy keep tripeing bracker,now theire is no cold air comeing out of united out side united feels like cool air out side now was hot air comeing out the fan earlily today
Tripping breakers on AC systems often mean a compressor motor is failing.
Also check for wiring shorts or burn-up.
Question: we see large pieces of ice accumulated inside the wall mounted unit
(Sept 21, 2014) Deena said:
If we have our mini split on for 8 hours, we see large pieces of ice accumulated inside the wall mounted unit. The air output also seems to be weak. We have pulled the filters are cleaned them. Other than air output, we haven't noticed anything wrong with the unit. Any suggestions? Thank you.
Ice accumulation can block air flow and thus reduce cooling effectiveness. On a cooling coil ice often means either a blocked dirty air filter on the return air side or low refrigerant.
Question: a heat pump stays in the defrost mode
(Oct 23, 2014) Anonymous said:
why does a heat pump stay in the defrost mode?
Look for a stuck or failed relay or control board
(Oct 23, 2014) Freitas said:
Our Fujitsu inverter air conditionig/heat pump,works perfectly on cool mode. But when we changed to heat mode it takes about 5 min to start. Then ventilation is very low and cold. After another 5 or 6 minutes the compressor stops as well as the inner ventilation. The "operation" green light remains still (no blinks), but the equipment won't start again. What can be happening?
Possibly there is a control board or relay problem, or the reversing valve is not operating. It's time for a service call. Keep us posted.
28 Oct 11 Anonymous said:
I have a Ruud split heating / air conditioning system. The unit outside will activate via thermostat control but the air handler in tha attic will not turn on and blow air. The breakers are not tripped. Any suggestions?
After confirming that the unit has power,
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