Air Con Questions

[gennisis]

According to what I have read on the internet a 10,000BTHU unit is OK for a 20 sq/mtr room.

I have 2 air cons and 2 similar sized rooms.

In room A all is well...in room B not so well as I find that the air from the unit is never cooler than 30C. The exhausted air from the outside compresser is not so hot as from the unit in room A.

Whatever temp I set for room B...say 27C.. the room temp never reaches it,,seems to be 30C whatever.

SO.. to me .. the unit in B is not operating as well as in A.

The engineer says that the unit is only 9,000 bthu and is too small.

Now,,as far as I can reason,if a unit is too small for the room,it will be running much longer to reach the set temp,maybe running continualy....but that the air from the unit would be cold...but not enough to lower the room temp.

So...my engineer says I need a bigger unit.

I say that if the existing unit was producing cold enough air it would simply need to keep running and gradualy reduce the room temp..

I question the unit for performance...maybe needs an injection of Gas?

Gentlemen...your comments and suggestions are welcome.

[T_Dog]

A refrigerant recharge is not expensive, so definitely worth a try before a new unit. In the past I have measured air between 17C and 19C coming out the evaporator fan units on older air conditioners. It sure sounds like your units are not working equally well.

[Pib]

If you are only getting a 30C/86F air at the A/C output vent something ain't working right. You should be getting around 15-20C/59-68F (or lower) at the vent output / a inch or so inside the vent. I just checked the output vent temperature about an inch inside the vent of my wall mounted split air unit set to 25C and the output vent temp was 14C/57F with my room cooled down to around 25C/77F.

Whether an A/C (pretty much any size) is trying to cool a small room or a warehouse, it should be able to achieve a temperature differential, repeat, differential, between it input/filter vent and output vent of around 15C say 5-10 minutes after being turned on. This differential would be "right at the vents." Like if the ambient/temp at the A/C input/filter vent was 32C/90F (remember, right at the vent), the air temp right at/just inside its output vent should be around 17C/63F after the A/C has been initially turned on and run about 5-10 minutes. I'm not saying your room temperature will now be 17C/63F; I'm saying the air temp right at/just inside the A/C output vent. Now, as the room ambient temp cools down that input-output temperature differential will get smaller as the A/C can only put out a certain "coldness/temperature" level....with that output vent temp probably staying right around 15-20C/59-68F (or lower) with the compresssor unit kicking on less often after the room cools down.

Now, when we get into cooling "capacity/how large of a room an A/C can cool down to a selected temperature" that's a whole different story/calculation. Obviously a 9000BTC A/C ain't going to cool a warehouse/big room too well, but the air "right at" its output vent should still feel cold.

If you have a thermometer you can get real close to the output vent (or better yet about an inch inside the output vent but not far enough to touch the fan) on both your 10,000BTU and 9,000BTU A/Cs you may want to compare output vent temperatures....sounds like you may find out the 9,000BTU is not putting out very cold air....I would think the output vent temperature of these similarly sized A/C would be close. Heck, just use your hand up against the output vent of each A/C to compare how cool/cold the air from the output vents compare...they should feel pretty much the same if both are operating properly.

Also make sure the 9,000BTU ain't set to Fan Only, Dry, or some other mode that may not cool at all or cool little...make sure it's set to "Cool" mode to get maximum cooling. If the air temp right at the vent output is still not-to-cool to just ambient temperature then it sounds like you have a broke A/C.

As I was writing this I check the vent out

[oldgit]

If your unit is short of gas,there will be icing where the refrigeration lines enter the outdoor unit.It could be a simple case of a clogged up indoor unit filter.

[gennisis]

If you are only getting a 30C/86F air at the A/C output vent something ain't working right. You should be getting around 15-20C/59-68F (or lower) at the vent output / a inch or so inside the vent. I just checked the output vent temperature about an inch inside the vent of my wall mounted split air unit set to 25C and the output vent temp was 14C/57F with my room cooled down to around 25C/77F.

Whether an A/C (pretty much any size) is trying to cool a small room or a warehouse, it should be able to achieve a temperature differential, repeat, differential, between it input/filter vent and output vent of around 15C say 5-10 minutes after being turned on. This differential would be "right at the vents." Like if the ambient/temp at the A/C input/filter vent was 32C/90F (remember, right at the vent), the air temp right at/just inside its output vent should be around 17C/63F after the A/C has been initially turned on and run about 5-10 minutes. I'm not saying your room temperature will now be 17C/63F; I'm saying the air temp right at/just inside the A/C output vent. Now, as the room ambient temp cools down that input-output temperature differential will get smaller as the A/C can only put out a certain "coldness/temperature" level....with that output vent temp probably staying right around 15-20C/59-68F (or lower) with the compresssor unit kicking on less often after the room cools down.

Now, when we get into cooling "capacity/how large of a room an A/C can cool down to a selected temperature" that's a whole different story/calculation. Obviously a 9000BTC A/C ain't going to cool a warehouse/big room too well, but the air "right at" its output vent should still feel cold.

If you have a thermometer you can get real close to the output vent (or better yet about an inch inside the output vent but not far enough to touch the fan) on both your 10,000BTU and 9,000BTU A/Cs you may want to compare output vent temperatures....sounds like you may find out the 9,000BTU is not putting out very cold air....I would think the output vent temperature of these similarly sized A/C would be close. Heck, just use your hand up against the output vent of each A/C to compare how cool/cold the air from the output vents compare...they should feel pretty much the same if both are operating properly.

Also make sure the 9,000BTU ain't set to Fan Only, Dry, or some other mode that may not cool at all or cool little...make sure it's set to "Cool" mode to get maximum cooling. If the air temp right at the vent output is still not-to-cool to just ambient temperature then it sounds like you have a broke A/C.

As I was writing this I check the vent out

Thanks PIb,you have said everything I had thought to be the case.

It rules out that maybe the thermostat is giving wrong info and cutting out the compressor,and shows me that the compressor just isnt working correctly. I intend to get the gas checked and refilled if nessesary...cant see how it can't be needed. If it isnt that then the compressor needs to be overhauled or replaced.

Edited April 25, 2012 by gennisis

[Naam]

Thanks PIb,you have said everything I had thought to be the case.

It rules out that maybe the thermostat is giving wrong info and cutting out the compressor,and shows me that the compressor just isnt working correctly. I intend to get the gas checked and refilled if nessesary...cant see how it can't be needed. If it isnt that then the compressor needs to be overhauled or replaced.

you have to check whether the compressor works at all. it either works or it doesn't, no such thing like "not working correctly". no hot air at the outside unit indicates considerable loss of refrigerant without icing of valves occurring. get the unit filled and problem is most probably solved.

[bankruatsteve]

FYI: I have 20m2 room cooled by 7000 BTU Mitsubichi ("Mr. Slim"). I set to 26 and the room is comfortable within minutes, very quiet both in/out, and runs very efficiently.

[rizla]

While we are on this subject, can anyone confirm if new AC`S come pre gassed...a friend just had one fitted and no bottles in sight..thanks

[cooked]

An over sized unit will lower room temperature quickly and shut off before humidity has been extracted sufficiently.

There is some good straight forward information on <URL Automatically Removed>

Edited April 25, 2012 by cooked

[cooked]

<URL Automatically Removed>

[Pib]

While we are on this subject, can anyone confirm if new AC`S come pre gassed...a friend just had one fitted and no bottles in sight..thanks

Windows ACs come pre-gased. And I think my split ACs came pre-gased (but I wasn't around for the entire install)....and when still living in the States my central air came pre-gased. The installers still needed to use a vacuum pump to evacuate air from the connecting lines between the compressor and condensor units, and whether they needed to add a little freon afters I guess depends on the distance between the condensor and compressor.

Edited April 25, 2012 by Pib

[rizla]

While we are on this subject, can anyone confirm if new AC`S come pre gassed...a friend just had one fitted and no bottles in sight..thanks

Windows ACs come pre-gased. And I think my split ACs came pre-gased (but I wasn't around for the entire install)....and when still living in the States my central air came pre-gased. The installers still needed to use a vacuum pump to evacuate air from the connecting lines between the compressor and condensor units, and whether they needed to add a little freon afters I guess depends on the distance between the condensor and compressor.

If you connect up your own (normal thru the wall install) is it a must to vaccum out the copper lines or will it be ok if the pipe run is only thru the wall, say 6 feet to the unit outside..thanks

[Pib]

As far as I know the air mixing with the freon would contaminate the freon, mess up the required system freon pressure, system wouldn't cool properly, etc.

[rizla]

As far as I know the air mixing with the freon would contaminate the freon, mess up the required system freon pressure, system wouldn't cool properly, etc.

Ok, thanks..maybe i need to look at way of sucking out the air in the pipes..

[gennisis]

Thanks PIb,you have said everything I had thought to be the case.

It rules out that maybe the thermostat is giving wrong info and cutting out the compressor,and shows me that the compressor just isnt working correctly. I intend to get the gas checked and refilled if nessesary...cant see how it can't be needed. If it isnt that then the compressor needs to be overhauled or replaced.

you have to check whether the compressor works at all. it either works or it doesn't, no such thing like "not working correctly". no hot air at the outside unit indicates considerable loss of refrigerant without icing of valves occurring. get the unit filled and problem is most probably solved.

UPDATE.......Engineer came,found low gas pressure...recharged...LUXURY !!

[Pib]

Thanks PIb,you have said everything I had thought to be the case.

It rules out that maybe the thermostat is giving wrong info and cutting out the compressor,and shows me that the compressor just isnt working correctly. I intend to get the gas checked and refilled if nessesary...cant see how it can't be needed. If it isnt that then the compressor needs to be overhauled or replaced.

you have to check whether the compressor works at all. it either works or it doesn't, no such thing like "not working correctly". no hot air at the outside unit indicates considerable loss of refrigerant without icing of valves occurring. get the unit filled and problem is most probably solved.

UPDATE.......Engineer came,found low gas pressure...recharged...LUXURY !!

Good deal...also makes the electric company smile a little more...they'll tell you how much more in your next electric bill since the unit's compressor will now be kicking-in and creating a full freon pressure load.

[gennisis]

Thanks PIb,you have said everything I had thought to be the case.

It rules out that maybe the thermostat is giving wrong info and cutting out the compressor,and shows me that the compressor just isnt working correctly. I intend to get the gas checked and refilled if nessesary...cant see how it can't be needed. If it isnt that then the compressor needs to be overhauled or replaced.

you have to check whether the compressor works at all. it either works or it doesn't, no such thing like "not working correctly". no hot air at the outside unit indicates considerable loss of refrigerant without icing of valves occurring. get the unit filled and problem is most probably solved.

UPDATE.......Engineer came,found low gas pressure...recharged...LUXURY !!

Good deal...also makes the electric company smile a little more...they'll tell you how much more in your next electric bill since the unit's compressor will now be kicking-in and creating a full freon pressure load.

After this last week with room temp in the 40's...a kings ransom is cheap.

Question....if the compressor was working,albeit only trying to compress the gas that was in the system,wouldn it have to be working all the time? whereas now it will cut out when the selected temp is reached?,so less electric will actualy used?

[Naam]

Good deal...also makes the electric company smile a little more...they'll tell you how much more in your next electric bill since the unit's compressor will now be kicking-in and creating a full freon pressure load.

After this last week with room temp in the 40's...a kings ransom is cheap.

Question....if the compressor was working,albeit only trying to compress the gas that was in the system,wouldn it have to be working all the time? whereas now it will cut out when the selected temp is reached?,so less electric will actualy used?

that's correct. Pib just wanted to pull your leg a bit.

[Naam]

While we are on this subject, can anyone confirm if new AC`S come pre gassed...a friend just had one fitted and no bottles in sight..thanks

in Thailand they normally don't. in Europe it is quite common that split units as well as piping are installed pre-gassed. the pipes have automatic valves which open when connected. if installed properly no vacuum pump required.

these valves are available in Thailand too but prices indicate that they are most probably 24k gold plated and studded with diamond dust.

Edited April 27, 2012 by Naam

[Pib]

After this last week with room temp in the 40's...a kings ransom is cheap.

Question....if the compressor was working,albeit only trying to compress the gas that was in the system,wouldn it have to be working all the time? whereas now it will cut out when the selected temp is reached?,so less electric will actualy used?

It depends on your A/C's/compressor's design. For some A/Cs when the freon gets too low the compressor won't kick in; on others it may run and run. My experience with my own A/Cs over the years, window, split air, and central air, is when to much of the freon leaks out the compressor won't kick in. Same thing happens with the A/C compressor on a car...when it's empty/too low on freon it won't kick-in; charge it up with freon and it kicks on....more personal experience.

Then you can get other cases where the freon is low but not too low which may cause the compressor to run a lot more/longer...and this low freon condidtion can cause freezing-up in your condensor unit....another problem I have personally experienced with my central air system back in the States before. When the condensor freezes up noticeable by a sheet of ice on the fins and probably a lot more water dripping out of the condensor drain hose due to freezing and melting ice, then little air flow can get through the ice-cold condensor fins...therefore you won't feel much of any cooling. So, whether your electric bill goes up or not will mostly depend on was the compressor in your unit "really" running before or was that just the fan motor you heard.

[exeter]

I find this topic interesting, 2 rooms of 20 sq m a room and 9000 btus units. I have room of 16.5 sq m and am told I need 12000 btus, so am a little confused, my room is a bed room, do I need 9000 or 12000btu?

[Pib]

I find this topic interesting, 2 rooms of 20 sq m a room and 9000 btus units. I have room of 16.5 sq m and am told I need 12000 btus, so am a little confused, my room is a bed room, do I need 9000 or 12000btu?

Gosh, how large an A/C you need is determined more than just room square meters. What's the total volume of the room in considering ceiling height also. How well is the room insulated? Is the roomed shaded or sunlite most of the day? How many people normally stay in the room and other heat load factors to consider? You can google along the lines of "How to size an AC" and come up with various sizing recommendations/calculators.

[lopburi3]

But in most cases a room that small will probably not require 12k (unless you like/require meat locker temps like Naam). We are comfortable with a wall top setting of 28 (which suspect is about 26 at sitting level) in our 26sm or so bedroom and 9k is keeping it at that comfortable level day and night. But this is ground level so no hot floor adding to the heat and some insulation above. I have an 18k in same bedroom and installed the 9k just as a backup several years ago but since then have only had to use the 18k unit a few times last year (when 9k was extremely dirty and could not keep up). To date this year fully comfortable with just the 9k and spend most of the day here.

For Thailand find the suggested size from HomePro and such to be excessive - but as said it will make a difference on what you require to be comfortable as well as the room/people factors.

[exeter]

But in most cases a room that small will probably not require 12k (unless you like/require meat locker temps like Naam). We are comfortable with a wall top setting of 28 (which suspect is about 26 at sitting level) in our 26sm or so bedroom and 9k is keeping it at that comfortable level day and night. But this is ground level so no hot floor adding to the heat and some insulation above. I have an 18k in same bedroom and installed the 9k just as a backup several years ago but since then have only had to use the 18k unit a few times last year (when 9k was extremely dirty and could not keep up). To date this year fully comfortable with just the 9k and spend most of the day here.

For Thailand find the suggested size from HomePro and such to be excessive - but as said it will make a difference on what you require to be comfortable as well as the room/people factors.

There are only 2 of us, the sun is on the house from about 9am to 4pm and I think there is no insulation, its a bedroom on the first floor and we would only be using the unit at night. I will go and have a look at the Home pro site but any other useful comments would be gratefull recieved, thanks and I hope no one minds me hi jacking the topic now that the original problem seems to have been solved.

[Naam]

For some A/Cs when the freon gets too low the compressor won't kick in; on others it may run and run.

usually the compressor kicks in, overheats after some time (lack of freon means also lack of lubricating oil) and switches off triggered by a thermal overload relay. that goes on and on till that relay is sick, tired because its contacts are burned. then, after some time, the compressor gets also sick and tired and either the piston (no matter rotating or old style up-down piston) freezes or the coil burns out.

[Naam]

But in most cases a room that small will probably not require 12k (unless you like/require meat locker temps like Naam). We are comfortable with a wall top setting of 28 (which suspect is about 26 at sitting level) in our 26sm or so bedroom and 9k is keeping it at that comfortable level day and night. But this is ground level so no hot floor adding to the heat and some insulation above. I have an 18k in same bedroom and installed the 9k just as a backup several years ago but since then have only had to use the 18k unit a few times last year (when 9k was extremely dirty and could not keep up). To date this year fully comfortable with just the 9k and spend most of the day here.

For Thailand find the suggested size from HomePro and such to be excessive - but as said it will make a difference on what you require to be comfortable as well as the room/people factors.

the average temperature in Naam's meat locker home is 26.5ºC measured approximately one meter above floor level. Naam feels hot @ 27º and shivers @ 26ºC. what Naam enjoys is going to bed in his bedroom which is cooled down to 18ºC. but then he switches off the big 'un, adjusts the thermostat of the small one to 26º and let the room slowly warm up. when Naam gets up in the morning (he is an early bird) Mrs Naam (who is a night owl) goes to bed and fumbles around with three remotes (2 AC remotes and a ceiling fan remote) but Naam couldn't care less.

[lopburi3]

I had the impression it was lower - perhaps you had mentioned wife liking it really cool or that 18 degree figure (which is definitely Arctic freezing for our blood).

[doggie888888]

I find this topic interesting, 2 rooms of 20 sq m a room and 9000 btus units. I have room of 16.5 sq m and am told I need 12000 btus, so am a little confused, my room is a bed room, do I need 9000 or 12000btu?

Gosh, how large an A/C you need is determined more than just room square meters. What's the total volume of the room in considering ceiling height also. How well is the room insulated? Is the roomed shaded or sunlite most of the day? How many people normally stay in the room and other heat load factors to consider? You can google along the lines of "How to size an AC" and come up with various sizing recommendations/calculators.

I am no expert and am unsure if ceiling height matters a lot? After all, cold air falls so I think the square meterage of the room matters more than ceiling height?

[nong38]

I find this topic interesting, 2 rooms of 20 sq m a room and 9000 btus units. I have room of 16.5 sq m and am told I need 12000 btus, so am a little confused, my room is a bed room, do I need 9000 or 12000btu?

Gosh, how large an A/C you need is determined more than just room square meters. What's the total volume of the room in considering ceiling height also. How well is the room insulated? Is the roomed shaded or sunlite most of the day? How many people normally stay in the room and other heat load factors to consider? You can google along the lines of "How to size an AC" and come up with various sizing recommendations/calculators.

I am no expert and am unsure if ceiling height matters a lot? After all, cold air falls so I think the square meterage of the room matters more than ceiling height?

That is what I would have thought as well, so a lightly used 9000 btu might well do the trick. I have noticed that Thai sellers always try to put you to a more expensive model, or/and a more powerful model than is actually required. Saving the planet and my wallets contents are not of the agenda here!

[Pib]

I find this topic interesting, 2 rooms of 20 sq m a room and 9000 btus units. I have room of 16.5 sq m and am told I need 12000 btus, so am a little confused, my room is a bed room, do I need 9000 or 12000btu?

Gosh, how large an A/C you need is determined more than just room square meters. What's the total volume of the room in considering ceiling height also. How well is the room insulated? Is the roomed shaded or sunlite most of the day? How many people normally stay in the room and other heat load factors to consider? You can google along the lines of "How to size an AC" and come up with various sizing recommendations/calculators.

I am no expert and am unsure if ceiling height matters a lot? After all, cold air falls so I think the square meterage of the room matters more than ceiling height?

That is what I would have thought as well, so a lightly used 9000 btu might well do the trick. I have noticed that Thai sellers always try to put you to a more expensive model, or/and a more powerful model than is actually required. Saving the planet and my wallets contents are not of the agenda here!

I sure wouldn't argue cold air is not heavy than hot air, but as the cold air falls through the hot air or the hot air rises through the cold air the cold air ends up not being so cold anymore. Plus you just have the interaction between the lower layer cool air and upper layer warm air in the room...where basically that warm layer is making the cool air less cool. Maybe take it to an extreme...say you had a room with a 20 ft ceiling height compared to a 10 ft ceiling height...you've just doubled the volume of air in the room requiring cooling. But many calculators I've seen really don't consider ceiling height since I guess they consider then all around 9 ft give or take a little except in some houses where vaulted/high ceilings exist which increase the volume of air needing cooling; but the ones which do a more accurate calculation do include ceiling height.