Inverter Air Con.

[CGW]

I have a air-con problem that I would like to throw out to the forum, hopefully some learned member may be able to give a satisfactory explanation?

I installed a 18k Mitsu Inverter air con in a bedroom that measures 7m x 5m, I have been told by 2 different Thai air con "experts" that the air con is too small for the room as it does not cool the room down adequatley.

I realised that the air con would be working hard for its existence from the begining, the reason I went with 18k was becausce the room is very well insulated, double walls, double glazing etc, but appears it is not big enough!

What I don't understand is why the compressor doesn't keep running and at least attempt to cool down the room! it just turns itself off and goes into hibernation! surely the compressor should keep running?

There is a NOTE: in the operating instruction manual "During Cool operation the set temp may not be changed when the room temp is more than 2 deg C higher than the set temp. In this case wait until the room temp drops to within 2 deg C of the room temp" I take it this means that you cannot cool the room by more than 2 deg C? - which is ridiculous!

If anyone has an explanation?

[Crossy]

Are you sure it's set to 'Cool' ? (I know, but one has to ask)

Set the control to the lowest it will go, it should have a good try at getting there with the compressor running constantly.

What is a little worrying is that the compressor is going to sleep, an inverter unit would normally change speed as the room cools but only actually stop when the set temperature is reached.

I have no idea what the instructions are suggesting, poor translation perhaps.

[CGW]

Definatley set to "Cool"

Tried stting to lowest temp etc, initially - sometimes it will try hard to get there! other times makes no effort! just plain bloody lazy perhaps?

I too do not understand why compressor stops running, but am told by "experts" that air con is ok!

The instructions are the same in the Australian edition so poor translation could well be the problem! any Aussies that can shine a light?

Cheers

[Pib]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

[MichaelJohn]

I have 2 x 24 BTU mitsubishi mr slim inverter and find them excellent.

I think your unit is under powered but that's no excuse for it to go to sleep

I dont have the instruction book to hand but recall there's two options for cooling. Once states the 2 deg stuff you're on about and then there's another cooling option where you set the temp?? Have you tried that?

If all else fails ring Mitsubishi; from my experience they will send someone FOC to resolve the problem.

[Pib]

You sure you have it set to "Manual" mode where you can manually selected the "Cooling" mode. I pulled down a manual on a model which may be like your unknown model number where it had that statement you mentioned but that statement was under the "I Feel Mode" which will automatically switch between Cool, Dry, and Heat modes which pulls down to some selected temp ranges and then you press the Too Warm or Too Cool buttons if it don't feel like a comfortable temp to you. I expect if set to the Manual mode and then you set it to Cool you would have the ability to pull the temp down lower...have more manual control.

Edited May 23, 2015 by Pib

[Anthony5]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

Rule of thumb is 700 Btu/sqm in Thailand. So 18000 Btu is too small for 35 sqm room.

[Pib]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

Rule of thumb is 700 Btu/sqm in Thailand. So 18000 Btu is too small for 35 sqm room.

I've got an 18K BTU in a bigger room than his will plenty of windows and it cools down to around 21C if desired. I live in Bangkok.

Plenty of A/C size calculators on the web...the OP can use them to come to his own conclusion based on room size, insulation, etc.

[Pib]

One other note for the OP, with an inverter "nominal" rating of 18K BTU, I expect it's actual BTU range is down to around 5K and up to around 20KB BTU. The inverter's "max" BTU capability is about 10% higher than its nominal rating. It will vary within this range to meet the BTU cooling requirement....higher when first cooling down the room...then tapering off to keep the room cool versus being completely off or running at 18K BTU like a fixed speed A/C....this BTU adjustment capability is the main way inverters save electric costs over fixed speed A/Cs.

[Anthony5]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

Rule of thumb is 700 Btu/sqm in Thailand. So 18000 Btu is too small for 35 sqm room.

I've got an 18K BTU in a bigger room than his will plenty of windows and it cools down to around 21C if desired. I live in Bangkok.

Plenty of A/C size calculators on the web...the OP can use them to come to his own conclusion based on room size, insulation, etc.

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Does that calculation take in account how many windows, which side the room is and more important that we are in a tropical country?

[Pib]

As mentioned earlier the OP can pull-up his own calculator which may offer a windows selection....but then how do you take into account window curtains/drapes/blinds. My room I mentioned earlier is approx 70% windows on two of the four walls...the third wall is is about 10% windows...the fourth wall no windows. The curtains are used to partially to totally block sunlight. Then of course at night sunlight coming through windows is not an issue....curtains are then used to keep away the peeping toms. My room is bigger than his...18K BTU is more than enough. Salesmen like to sell over sized A/Cs because they cost more and to play it safe cooling-wise...of course getting an A/C that is too large, especially a fixed-speed A/C, may result in insufficient humidity reduction which has an impact on how cool a room feels.

Edited May 23, 2015 by Pib

[KhunBENQ]

Does that calculation take in account how many windows, which side the room is and more important that we are in a tropical country?

Maybe not.

We use our ACs mainly during the night for sleeping.

A 13k inverter for 18 sqm has an easy job with that (running slow).

If you have big windows to the (north-)west (afternoon sun) at this time, good luck with 18k for 35 sqm.

Edited May 23, 2015 by KhunBENQ

[CGW]

As I said I realise 18k is minimal for a room this size, but given AC is not run in the day and insulation and windows are about as good as you can get in Thailand I though/hoped it would be ok, as Pib states salesmen will always oversell BTU which leads to extra running costs/less efficiency.

Mitsubishi have sent 2 experts to look at "problem" they both state AC too small for room, after performing some lenghy tests, - I can accept that! but why isn't the compressor running all the time? rather than ramping down to a sleep mode, if the compressor was screaming all the time AC was running I would happily accept that it was too small. This AC was one of five (MSY-GK???) that were fitted at the same time, the others have been no problem.

MichaelJohn, I have reread manual and can only see what I posted re: 2 deg in cool modeno other option?

Cheers

[harrry]

I have an inverter and it does shut down occasionally. If the air temp is within 2 degrees of the set temperature it thinks it does not have to work. This then becomes a humidity problem but that is solved by running it in dry. This happens mostly at night. If the range is higher it does just run more slowly.

Edited May 23, 2015 by harrry

[Anthony5]

As I said I realise 18k is minimal for a room this size, but given AC is not run in the day and insulation and windows are about as good as you can get in Thailand I though/hoped it would be ok, as Pib states salesmen will always oversell BTU which leads to extra running costs/less efficiency.

Mitsubishi have sent 2 experts to look at "problem" they both state AC too small for room, after performing some lenghy tests, - I can accept that! but why isn't the compressor running all the time? rather than ramping down to a sleep mode, if the compressor was screaming all the time AC was running I would happily accept that it was too small. This AC was one of five (MSY-GK???) that were fitted at the same time, the others have been no problem.

MichaelJohn, I have reread manual and can only see what I posted re: 2 deg in cool modeno other option?

Cheers

I have Daikin inverter aircons and they also stop completely at one point.

Inverter aircons will have variable speeds, thereby regulating the current they use, but at one point they do completely stop .

Edit to add:

An inverter aircon slows down when it almost reaches the set temperature, but stops completely when it reaches the set temperature, then starts again slowly when the temperature rises above the set temperature.

http://www.refrigeration-engineer.com/forums/showthread.php?40129-Panasonic-Inverter-Compressor-Stops

Edited May 23, 2015 by Anthony5

[CGW]

"An inverter aircon slows down when it almost reaches the set temperature, but stops completely when it reaches the set temperature, then starts again slowly when the temperature rises above the set temperature."

And therein lies my problem! it doesn't do this!

Edited May 23, 2015 by CGW

[Anthony5]

"An inverter aircon slows down when it almost reaches the set temperature, but stops completely when it reaches the set temperature, then starts again slowly when the temperature rises above the set temperature."

And therein lies my problem! it doesn't do this!

Well in your OP you say that the compressor turns off.

So what is it that it doesn't do? Reach the set temperature? What is the set temperature?

[IMHO]

I also have a 35sqm room, and have just replaced a 24K BTU unit with a 36K Btu unit, because the 24K unit was just not up to the job when outside temps approach 40c (at low-mid 30's it worked OK). North facing room, well insulated, also double block, etc.

I've learnt the hard way - good implementation of "cool" construction techniques doesn't mean you can downsize your AC - it just means you might save some money on AC bills... No matter how hard you try, for example - you're only making something with a tiny, tiny fraction of the insulation properties of say, a commercial cool room

Edited May 23, 2015 by IMHO

[IMHO]

"An inverter aircon slows down when it almost reaches the set temperature, but stops completely when it reaches the set temperature, then starts again slowly when the temperature rises above the set temperature."

And therein lies my problem! it doesn't do this!

Indoor unit has probably iced up, and the system shuts down to let it recover.

Your AC is too small, no question.

[Naam]

any comment is nothing but a waste of time until the OP tells us what the set temperature is and what actual temperature his unit achieves. period!

one of our bedrooms is about the same size, has three outside walls and borders a non-airconditioned passage but its 13k btu/h unit can cool it without any problems to 24ºC when ambient temperatures are 35-36ºC. it takes of course more than 5 minutes and 20 seconds to reach that temperature

[Crossy]

Add to the above the temperature of the air exiting the indoor unit.

[Pib]

Maybe include the complete model number also...you mentioned the first part of it as "MSY-GK." What's the complete model number?

[CGW]

any comment is nothing but a waste of time until the OP tells us what the set temperature is and what actual temperature his unit achieves. period!

one of our bedrooms is about the same size, has three outside walls and borders a non-airconditioned passage but its 13k btu/h unit can cool it without any problems to 24ºC when ambient temperatures are 35-36ºC. it takes of course more than 5 minutes and 20 seconds to reach that temperature

Temp set for 23c, generally reaches 25/26c, if I turn the temp down to 18/19 seems to make no differnce nor does the compressor kick in!

Maybe include the complete model number also...you mentioned the first part of it as "MSY-GK." What's the complete model number?

MSY-GK 18VA.

[Chao Lao Beach]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

Rule of thumb is 700 Btu/sqm in Thailand. So 18000 Btu is too small for 35 sqm room.

So many of these figures are is for 15'c, if you are normal and leave it at about 26'c, it will be fine.

Inverter AC duck in Thailand, the huge range in voltage gets em.

[Anthony5]

18K BTU is definitely more than big enough for a 7M x 5M room (and assuming a 3M height).

Rule of thumb is 700 Btu/sqm in Thailand. So 18000 Btu is too small for 35 sqm room.

So many of these figures are is for 15'c, if you are normal and leave it at about 26'c, it will be fine.

Inverter AC duck in Thailand, the huge range in voltage gets em.

I have to see the first aircon that has a 15° setting, and what huge range in voltage there is in Thailand, and how does that make a difference compared with conventional aircon?

[Anthony5]

any comment is nothing but a waste of time until the OP tells us what the set temperature is and what actual temperature his unit achieves. period!

one of our bedrooms is about the same size, has three outside walls and borders a non-airconditioned passage but its 13k btu/h unit can cool it without any problems to 24ºC when ambient temperatures are 35-36ºC. it takes of course more than 5 minutes and 20 seconds to reach that temperature

Temp set for 23c, generally reaches 25/26c, if I turn the temp down to 18/19 seems to make no differnce nor does the compressor kick in!

Maybe include the complete model number also...you mentioned the first part of it as "MSY-GK." What's the complete model number?

MSY-GK 18VA.

I think that explains your problem, as another member has mentioned already. Your set temperature is too low for the capacity of the unit you have, which make freeze it up.

[billphillips]

If your 18k unit is undersized for the room, it will run the external unit constantly in a vain attempt to attain your temperature setting. I don't think it's undersized, but beware of windows, walls and roofs exposed to the sun (solar gain). Double glazed windows are not protection from sunlight. Same, but to a lesser extent, for walls and roofs.

I do think that your selected room temp is a little unrealistic. With an outside temp in the high 30s, the most you should try to achieve is a reduction of 10c. For example say around 26 or 27c. But that is a "by the way" and of no importance to your current problem.

Your experts probably have little or no experience, other than a new installation so try this .... Firstly, put new good quality batteries in the remote control. Weak batteries will send the wrong signal to the wall unit. Secondly, check the electrical cable used and the quality of the connections made. An aircon should have a single unjoined cable direct to the distribution board and with its own breaker. Thirdly, now you need to check the gas in the system for pressure / content. The best plan for that is to drain and replace, making sure that the gas is exactly as detailed by the manufacturer. Before you do that a rough sort of test for the gas is to feel the pipes just as they enter the outside unit. One should be very cold to the touch, the other should be around the ambient temperature. If both of the pipes feel cold it may suggest that too much gas or pressure or the wrong gas has been mixed with the shipped unit. If the new batteries and cabling seem ok, I feel sure that both of your pipes will feel cold.

[harrry]

Your manual that came with your airconditioner will in the specifications setting have an operaing range. I will give a maximum number of degrees below ambient it can cool. Check you have not exceeded that.

[Anthony5]

If your 18k unit is undersized for the room, it will run the external unit constantly in a vain attempt to attain your temperature setting. I don't think it's undersized, but beware of windows, walls and roofs exposed to the sun (solar gain). Double glazed windows are not protection from sunlight. Same, but to a lesser extent, for walls and roofs.

I do think that your selected room temp is a little unrealistic. With an outside temp in the high 30s, the most you should try to achieve is a reduction of 10c. For example say around 26 or 27c. But that is a "by the way" and of no importance to your current problem.

Your experts probably have little or no experience, other than a new installation so try this .... Firstly, put new good quality batteries in the remote control. Weak batteries will send the wrong signal to the wall unit. Secondly, check the electrical cable used and the quality of the connections made. An aircon should have a single unjoined cable direct to the distribution board and with its own breaker. Thirdly, now you need to check the gas in the system for pressure / content. The best plan for that is to drain and replace, making sure that the gas is exactly as detailed by the manufacturer. Before you do that a rough sort of test for the gas is to feel the pipes just as they enter the outside unit. One should be very cold to the touch, the other should be around the ambient temperature. If both of the pipes feel cold it may suggest that too much gas or pressure or the wrong gas has been mixed with the shipped unit. If the new batteries and cabling seem ok, I feel sure that both of your pipes will feel cold.

The OP mentions that Mitsubishi technicians have performed lengthy tests. My experience with technicians from the manufacturer is that the first thing they do when arrive is checking the pressure of the refrigerant.

[harrry]

http://www.mitsubishielectric.com.au/assets/LEG/MSZ-FA-GA_MFZ-KA_MXZ-A_OBT14A.pdf

Although this may not be your model as regional numbers vary read page 5 and 6