Mitsubishi Mini Split Humidity Issues
suckmykiss182
| Posted in General Questions on
I apologize in advance for the long post, I am trying to make sure I provide all relevant details. We have a Mitsubishi Mini Split System Installed, model SLZ-KF-12NA. It has two ceiling cassettes, one in our bedroom and one in our family room. The system is just shy of 3 years old.
About two months ago we noticed our bedroom was getting very warm, even when it showed to be 69 in there. It took us a few weeks to realize what we were feeling was humidity. I ordered an indoor thermometer with humidity reader and it was about 69% humidity in our bedroom. We also noticed the condenser drip line off our bedroom was not putting out any water. The one off the family room still seemed to be dripping.
I called my usual AC guy and he checked the temp of the AC blowing into out bedroom. It was about 72-74, even though it was set to 69. At this point we weren’t able to get the temp below 70-71. He reset the system and it started blowing cold air- thank goodness!! We were so relieved. The humidity started dropping and within about 30 mins it was in the 40% range. He left and I went back to work.
When I got home, the humidity was about 71% and the air blowing was no longer cool. Thankfully I had already ordered a dehumidifier for our bedroom and it was delivered that afternoon. I got it hooked up and it definitely helped.
We realized that the family room (right next to the master bedroom) also seemed to be getting humid, so we placed a temp gage with humidity reader in there. It was humid, but at that point we were unclear if it was because we were keeping the bedroom door open.
I purchased a second dehumidifier for that room.
I have been emptying both of the dehumidifiers about 1 x every 5 days. They hold a fair amount. With the dehumidifiers I was able to keep it in the 50%-60% humidity range… but obviously still miserable.
My regular AC guy is not a certified Mitsubishi tech so he has told us over about a three week period that he had been trying to reach out to them for support and they wouldn’t talk to him.
Out of desperation and a lot of googling, I figured out how to put both of the cassettes into drying mode, which has helped immensely.
When I got the units both into drying mode it started blowing cold air again. If I have it set at 69 it easily gets down to 67. I can keep the humidity between 40%-48% for the most part. I also have the fans set to low.On Monday, our AC guy finally told me to call another company that is a certified dealer. The new company came out yesterday and the first thing he did was blow out the condensation line off the bedroom side of the house. When he blew out the line, I heard a pretty loud noise, I can’t really describe it. We both thought he had fixed the issue, but he was going to wait for the humidity to go down.
About a half hour later he came and told me that the humidity had actually went up a few degrees. I was obviously super surprised. He said he was going to have to schedule another appointment for him to come out and charge up the unit. I asked him when that would be and he said his office would call me.
I am worried that maybe the clog in the line (if there was one) was blown in deeper and clogged it more? The AC office did not call me so I had to call them to inquire about the follow up appointment. It was super clear they had no desire to help us and suggested we try other companies that have more experience with Mitsubishis. I don’t know why they didn’t say this in the first place, since I explained very clearly what we have and what the issues are with it when I called in.
If I put the units into Cool mode and turn off the dehumidifiers, the humidity will climb right back up.
I live in a very, very hot, dry part of California and we have never, ever had a humidity problem in the house. It very rarely gets humid here and our summer temps sit at about 112. Today it is 104 outside and the humidity is 11%. Inside it was 50% humidity in the bedroom and 45% in the family room. Drying mode has been running for about a month now. We are getting desperate and would appreciate any advice that you can offer!!If you got this far, thank you so much for reading and thank you in advance!
Edited to address comments below:
1. The unit is only “cooling” when running in drying mode. I set it for 69 at night and it quickly gets down to 67-66.
2.The fan does not run continuously, I turned that function off when we first started having issues.
3. The unit BTU is 12,000 each cassette. The bedroom is 615ish sq ft and the family room is 420 sq ft (ceilings are very high). If it is oversized, why are we suddenly having this issue after almost 3 years of no issues?
4. I did just have a thought… the second cassette unit wasn’t installed until last summer, as we were still finishing the family room. We did not have this issue (that we noticed) running both cassettes at the same time, with the doors closed. Maybe we didn’t notice it?
5. Yes, we are in a VERY dry part of California. Humidity is incredibly rare, unless its winter. Its definitely an internal issue, just not sure what.
6. I have tried only running one unit but that doesn’t seem to make a difference in either room.
7. The fan has been on low for a month now.
1. The unit is only “cooling” when running in drying mode. I set it for 69 at night and it quickly gets down to 67-66.
2.The fan does not run continuously, I turned that function off when we first started having issues.
3. The unit BTU is 12,000 each cassette. The bedroom is 615ish sq ft and the family room is 420 sq ft (ceilings are very high). If it is oversized, why are we suddenly having this issue after almost 3 years of no issues?
4. I did just have a thought… the second cassette unit wasn’t installed until last summer, as we were still finishing the family room. We did not have this issue (that we noticed) running both cassettes at the same time, with the doors closed. Maybe we didn’t notice it?
5. Yes, we are in a VERY dry part of California. Humidity is incredibly rare, unless its winter. Its definitely an internal issue, just not sure what.
6. I have tried only running one unit but that doesn’t seem to make a difference in either room.
7. The fan has been on low for a month now.
Thank you everyone for chiming in!
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Replies
It is not the drain line, if the drain line backs up you will get water on the floor.
I am not familiar with multisplits[2 heads on one compressor] but this is not operating correctly at all.
AS a guess, force the fan to low and set the temp to a low temperature. If the units are massively oversized this might be the issue.
Thank you so much for taking the time to respond! The fan has been on low for about a month now. When I have it in drying mode and I set it 69, it pretty quickly gets down to about 66-67.
Are they oversized? The unit BTU is 12,000 each cassette. The bedroom is 615ish sq ft and the family room is 420 sq ft (ceilings are very tall). If it is oversized, why are we suddenly having this issue after almost 3 years of no issues? I appreciate your input!
This is not my specialty, but a few thoughts:
I would never call 50% humidity miserable. In fact it would be quite good around these parts and is in the optimum zone. That said, since you are in an arid climate, I suspect the expectations are different.
112 degrees F at 11% humidity is a dewpoint of 45. If cooled to 70 degrees that's an RH of about 41. So either your numbers are off or your source of moisture is internal.
As far as equipment... unless there is some sort of sefety switch, a clogged drainline would not affect the ability to draw moisture from the air, it would just eventually overflow. What affects the ability to draw moisture is the temperature of the coil and airflow.
Is your place well sealed and insulated?
Thank you for commenting! Even if this isn't your area of expertise, I appreciate you trying to help. Where I am at, 50% is miserable. LOL We never get humid.
And yes, these rooms are incredibly well insulated and sealed. We just finished the remodel last year and hubby took everything down to the studs. He is super attentive to every little detail and too much of a perfectionist.
Glad to know it is not the drain line. How can we check the temp of the coil and airflow? Hubby plans to climb up into the attic this weekend to check the unit, but I hate for him to do that. He is a tree faller by trade and works very long days. I hate for him to come home to a muggy house and then to climb in the attic on the weekend.
This sounds like the typical combination of oversized multi split and continuous fan operation.
By default on most units the indoor fan runs 24/7. This is not an issue if the system is sized right and the system is modulating all the time.
With an oversized system, instead of modulating, the system tends to cycle so what happens is after the short cooling cycle, the continuous fan operation re-evaporates the moisture that condensed on the coil. This typically results in very poor humidity control.
If this is indeed your case, there is not much you can do about the sizing. You can fix the continuous fan operation though. Take a look at the application note here:
http://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10009/Application%20Note%201033%20ME%20-%20Indoor%20Fan%20Continuous%20Operation%202019%2004%2025.pdf
This change won't fix the rest of the issues associated with oversizing but should help with humidity.
P.S. As others have said, clogged drain does not create humidity issues. I've had it happen to me plenty of time, the only thing a clogged drain does is flood your house.
Thank you for going into so much detail in your response. I will show this to my husband when he gets home. The fan does not run continuously, I turned that function off when we first started having issues about a month ago.
The unit BTU is 12,000 each cassette. The bedroom is 615ish sq ft and the family room is 420 sq ft (it has very tall ceilings). If it is oversized, why are we suddenly having this issue after almost 3 years of no issues? I appreciate any additional insight you can offer, thank you!
This link is super informative, thank you!! I have had a really hard time getting clear information on our unit that only an installer would know. I will share this with husband for future reference.
If the system has been running fine and all the sudden things are off, it definately sounds like a refrigerant leak. Multi splits tend to operate in strange ways when low on refrigerant, I would have them check that first. The proper way to check this is to reclaim the refrigerant and weight it.
If the refrigerant is low than you have leaks, make sure they find them before refilling as you'll be back to the same problem a year or two down the road. Most of the time it is leaky flare but there have been reports of coil leaks in houses with open cell spray foam.
This will hopefully be our next step!
It sounds like the unit isn't running at all, the fan is blowing but no cooling is going on. When it does actual cooling it sounds like it's working fine. Is it possible that a neighboring room is providing so much cooling that the thermostat never clicks on?
Try turning off the units in neighboring rooms and see if that makes a difference.
The unit is only “cooling” when running in drying mode. I set it for 69 at night and it quickly gets down to 67-66. I do agree that it feels like only the fan is running when in cooling mode.
I have tried only running one unit but that doesn’t seem to make a difference in either room. Any other ideas? Thank you so much for taking the time to respond, I appreciate it!
If the thermostat is set for 69 and the room is at 66 or 67 it's not going to be cooling. If it's not cooling it can't dehumidify.
I am open to any suggestions!
Not that this comment will help you but maybe someone else might read this before they install an oversized multi head miny split as it seems to be the recipe for an unhappiness.
Is installing 2 smaller outdoor unit to replace the current outdoor unit in you budget?
Walta
It sounds like the units are not functioning correctly. There is no condensate coming out of the drip line in one room and the discharge temperature is 72 to 74. The unit works in dry mode but not in cool mode. I would have the units serviced because it sounds like a control problem and maybe the charge is off. The first unit worked fine for almost three years.
A 615 sf bedroom with high ceilings in 112-degree heat without knowing the amount of South facing windows may not be that oversized. The units may be oversized but in this case I don't think it is the main problem.
Thank you for your response and for clarifying the confusion! You have said everything I have been saying on repeat for the last two months!
In the rooms we are having issues in, we have two large south facing windows one is 4' x 8' and the other is a 4 x 5. We do not have any trees in the backyard that provide the house shade.
I really dont think they are oversized. Our ceilings are incredibly high and we have huge windows. The back of our house is full sun every day.
If they were oversized, why are we just now having this problem after almost 3 years of working correctly?
And no, it isn't. We've put over $40k into this remodel already. :(
I don't believe you've stated exactly which outdoor unit you have... this could also be quite oversized. But with the prevailing outside temperatures, your cooling load is going to be higher than many of us are used to considering.
Do you have any ventilation? Trickling in that dry outside air should help the situation.
But the symptoms you describe could point to a refrigerant problem or leak. You mentioned one tech said he'd be back to add more charge--be careful with this. With R410A you can't just gauge what's needed and add a spritz. The system needs to be evacuated and then the refrigerant weighed back in based on the equipment and linesets. I wonder if they got it right when the second unit was added?
Thank you for responding. The second tech is not coming back, they decided they didnt want to deal with it. :(
Do you think a leak would cause the humidity? Why does it cool in dry mode but not in cooling?
How can we tell if there is a refrigerant problem? If we can figure out how to trouble shoot it to know what the issue is, then we could tell someone what to do to fix it...since no one around here seems to want to get involved.
We do not have ventilation, because it is so hot outside. Even at night we aren't getting out of the 90s. We do leave the doors open between the rooms so that seems to help some.
Today its 112, 10% humidity outside and Ive got 50% humidity in the house. I just turned the dehumidifiers back on.
Yesterday I turned off the ac and dehumidifier, opened up the house and dried it out. I got the humidity down to 28% in one room and 30% in the other (it was only 11% outside). I then closed the house back up and turned the mini split on in cooling mode. Humidity started creeping back up and got to the 40% range. No cold air was coming out of the units, so put it back into drying mode. It cooled down and humidity didnt climb past 35-40%. When I got back home at noon today, humidity was up to 50% inside. Units are still in drying mode and I just turned my dehumidifiers back on.
The outside unit is MXZ-2C20NA2. We are in zone 9. Our coolest summer days are 100, and its not unusual for us to reach the teens. It is HOT here from May-September- very, very dry.
"I then closed the house back up and turned the mini split on in cooling mode. Humidity started creeping back up and got to the 40% range. No cold air was coming out of the units, so put it back into drying mode."
This doesn't quite add up to me. When you closed the house back up, did it cool down? If so, how, because you are saying there was no cooling provided. If it DIDN'T cool down, then how did relative humidity go up?
I'm not the expert but I would listen to those suggesting you have low refrigerant. Dry mode may be working better than cool, but it sounds like it's still not quite right.
Sorry if I didn't explain myself well. When I opened up the house, it heated up inside quickly and it took out the humidity.
When I closed the house back up, turned on the mini splits, the temp slowly came down while in cooling mode as the humidity started to rise.
Since it wasn't actually blowing cool air, I went ahead and put it back into drying mode. It took the house from 78 back down to 70ish. Essentially the purpose of me shutting everything off and opening up the house was was to dry it out, which worked great, until I closed the house back up and turned the mini split on.
I agree its definitely not working right. We talked to a AC tech this afternoon who does work on Mitsubishis, but he is booked out a few weeks. I appreciate you chiming in!
Hmm, this is tough. Only a tech can explore those refrigerant and installation questions (actually, you could do it by watching a bunch of YouTube, then getting online EPA certification and a few hundred bucks of tools. Ain't nobody got time for dat.)
What about setup parameters, such as where the units sense indoor temperature? (I would think it's best at the remote, could be problematic with ceiling cassettes if they're using return air temperature since supply is so close.) There are humidity-related settings, which should mostly be disabled since you don't have integrated ERV or dehumidifier., but perhaps they got wonky?
Do the units need a good cleaning? Those cassettes have such wimpy filters, and the fins are VERY easily clogged up if you have a dusty home.
My money is on a faulty installation leading to a slow leak, or a miswired com cable, something like that. The unit's dry mode is a specialized set of routines that can somehow squeeze some cool out of the setup, but there's something sabotaging what these machines are capable of.
Hi ohioandy! Our thermostats are wall mounted and they are not too terribly far from the cassettes. The family room one is about 8' away and the bedroom one is about 4' away.
I do keep our filters clean, is there anything else inside the cassette I should be dusting? Our house doesn't seem to be dusty, but it's worth checking. I will ask the tech that comes out next (whenever that is LOL) to give them a good cleaning.
And thank you for not telling me to get my EPA certification, like the mean guys do on the reddit AC help board. Man, it's rough over there!! So glad I found this board.
Air at 110F and 10% relative humidity has a dewpoint of 41F. That's the same moisture content as air at 68F and 40%RH. In that environment I would expect almost no dehumidification to be happening.
Sorry I dont fully understand. Are you saying that my opening up the house with 10% humidity outside wouldn't have dehumidified the house?
Not by much.
Hot air can hold more moisture than cold air. When humidity is represented as "relative humidity," it's relative to how much moisture it can hold at that temperature. Air at 110F can hold about 380 grains of water per pound of air. (A grain is a very small unit of weight). Air at 68F can hold about 100 grains of water per pound of air. When we say that the air is at 10% humidity, that's 10% of its carrying capacity, so for air at 110F that means 38 grains per pound. Air at 68F at 38 grains per pound is at 38% of its capacity, so 38% relative humidity.
Heating or cooling air doesn't by itself change the absolute humidity -- the grains per pound. So if you bring in air at 110F and 10% RH and cool it to 68F it's going to be at 38% RH. The exception is if you cool it below its dew point -- the temperature at which, with the current moisture content, the relative humidity becomes 100%. Relative humidity can never exceed 100%, if you cool below the dew point the moisture condenses out of the air as dew or condensation.
At 110F and 10% RH the dew point is 41F. That's pretty cold, the coil in your cooling head might get that cold, but it might not. If it doesn't, no dehumidification takes place.
Two things stick out at me about your description: first, the system worked for a few years and then stopped. That's a huge red flag. Something changed. You need to find out what it was and change it back. As others have noted, the most common issue with air conditioners is a refrigerant leak.
The second thing that sticks out is that you're finding 68F and 50% relative humidity uncomfortable. For most people that would be pretty ideal. I would wonder about the measuring device.
@DC_Contrarian, for some reason it wouldn't let me reply to your last comment.
The reason we find the high humidity uncomfortable is because its never humid here and we have never had a humidity problem in the house. I know it's very different in the south or the east- but think of driest part of Arizona, there is almost no humidity. That is what it is like in our area of California.
Thank you for going into more explanation on the humidity/dew point. It's very confusing to me but I am doing my best to understand. The only thing I can say is that when I opened up the house the other day, the outdoor temp 110 and the humidity was 10%. I took pics of both of my indoor thermometers before I did that, which are attached showing what it was like inside before I opened house. The second set up pictures are right before I closed the house back up. Maybe this will help? More pics in next reply.
The 3rd set of pictures are what it currently looks like. Both units still in drying mode and dehumidifiers running for the last few days. And finally, the last set up pictures are what my thermostats currently look like.
OK, I see the following pairs of temperature/relative humidity:
69F/46% RH
70F/44% RH
73F/40% RH
75F/ 36% RH
82F/28% RH
Those correspond to dewpoints of 47F, 47F, 47F, 46F and 46F. I would say those all represent the same absolute humidity within the accuracy of the device. So letting in outside air is not decreasing the absolute humidity at all, it's just making the air warmer.
But this is a sidetrack. If the system used to keep you comfortable and now it doesn't something has changed. We need to focus on what has changed. What very well could be happening is that your system is low on refrigerant so the coil isn't getting as cold as it used to. If you coil doesn't get below 46 or 47F it's not going to dehumidify at all.
@DC_Contrarian Thank you again for the taking the time to respond. We do have a certified tech coming out... we just don't know when. They are supposed to call me on Monday to see when they can get me on their schedule. They said it could be a few weeks out. I would by dying from the heat if the drying mode wasn't working for us.
My husband and I were talking last night about the charging of the unit. His best recollection is that he installed both cassettes at the same time and that our AC guy came out and charged them after that. We started using the bedroom one right away (three years ago in October) and then we started using the family room one at the end of last summer.
What I am wondering is...maybe something wasn't done with the second unit that needed to be. I know our tech was outside in the sun for hours doing the charging, but I dont recall the second cassette being hooked up at that time. My husband is sure it was.
At any rate, I do agree we need to get someone out here to fix it. Humidity issue aside, its definitely not blowing cold air in cooling mode, so that is a problem we need to fix. I finally bought one of those little sensor guns that you point at the ac register to test the temp. Right now the bedroom one is blowing about 51 degrees and the family room one is blowing 71. The family room is definitely having trouble cooling down.
You guys have definitely helped me understand this better so I can be more proactive.
Interesting little addition, the other end of the house, which is on a central ac and has a closed door to this part of the house has humidity about 38%. Now that I type that out, I just had a thought. We do have a vent that blows the central AC into our family room. It's on the opposite side of the room from the mini split cassette and thermostat. Could that be causing any of cooling issues?
Oh! And one last question- our thermostats are mounted somewhat close to to our cassettes- about 4-5' away. Should we move them so they are in the center of the room? I have noticed the temperature sayings its say 69, but it's actually 71 in the middle of the room.
Thank you for being a sounding board!!
Some thoughts in no particular order:
1. As DC_Contrarian and others have noted, if you bring the high temp low humidity outside air in, then cool that same air, the lower temp of the air will measure a higher RH, with the exact same absolute value of moisture in the air. That is to be expected.
2. As DC_Contrarian and others have noted, most people strive for indoor RH at about 50%. If you do some research on healthy humidity range for human occupancy, most say 35--40% RH min. It would not surprise me at all if the Mitsubishi system is not capable of bringing the RH humidity below that, given the coil temp, etc. In my area (hot/humid in many months of the year, then cold/dry for a few months) some people have dedicated dehumidifiers to get the RH down to 50% in the summer AND dedicated humidifiers to get the air up to 50% in the winter.
3. As to why your system worked for 3 years and now it doesn't: Something changed. I can think of four obvious possibilities based on your post.
a. If this is the first summer you have had the 2nd unit hooked up and running: with one indoor unit the system worked fine but something happened/was not done correct when the second indoor unit was installed/connected.
i. Since you have a 2 indoor to 1 outdoor unit setup, do you have a branch box that directs refrigerant to each indoor unit? If not, does your setup require one? If so, does the branch box have valves and were they all appropriately adjusted when the second unit was brought online?
ii. When the 2nd unit was brought online, was the refrigerant evacuated from the entire system and then put back at the appropriately calculated weight for the two heads, taking into account the exact length and size of the linesets from the heads to the branch box, and from the branch box to the outdoor unit? Were the branch box valves properly set during this process? Where are the calculations on length, size and refrigerant weight written down?
To address the above, you need to talk to the person (not company, specific person) who brought the 2nd unit online. You need to figure out a way to ask them to explain exactly what they did without giving them the clues about what they were supposed to do, because if you just ask "did you do or not do x" many installers will just confirm they did it even if they did not as they may be embarrassed by their error and/or don't want to be responsible for the cost of evacuating and then recharging the system.
b. If everything in a. was done correctly, it is possible something is leaking, has malfunctioned or is broken. These systems are difficult to troubleshoot.
c. It is possible system is either not sized properly or that it is working properly but that the design specs don't meet your expectations for dehumidification.
d. Something else in your household changed - ie your bath exhaust fans are not removing humidity as well as they did before, food prep has changed to put more humidity into the air, you installed an indoor sauna or hot tub, etc. You get the idea. Think about ANYTHING that may have changed since the system was working.
4. Where are the t-stats that are controlling these heads? Do you control them from a handheld remote that resembles a TV remote? It is my understanding that type of control communicates with a tstat inside the indoor unit. In that case, you may have some issues of the t-stat being too close to the supply. Or is it a remote wired or wireless unit, such as the MRCH unit that has an integral t-stat? In that case, please describe the location the remote tstat is wired or kept. That could influence the operation of the unit. Also, regardless of what type of tstat setup you have, is it showing any sort of error code?
5. As to how to get this fixed if it is something with the system and the installer who installed the 2nd indoor unit won't deal with it - this is a REAL problem, and although this should be a Mitsubishi problem it has turned into an end user problem. Mitsubishi will sell these things to ANYONE, but they will only do troubleshooting with the firms signed up to be their dealers. Even if you locate a Diamond or Diamond Elite certified Mitsubishi dealer, that is absolutely NO guarantee you can get this fixed.
My experience is my builder used a non-certified but highly skilled installer, who only does new installs and refuses to even answer the phone from anyone but the select few builders they work with, so no service from them. My experience with Mitsubishi service is:
a. One Diamond Elite dealer who came out and had obviously NEVER been trained on or perhaps even seen a ducted mini with branch box. Spent 2.5 days working on the unit, including hours on the phone with Mitsu getting schooled. Overcharged the system, then had to evacuate and recharge it properly. Charged for all 2.5 days of learned and unnecessary work., amounting to several thousand. So a service call for about 25% of what it cost to install the entire system new to begin with.
b. Next time called a different Mitsu Diamond dealer. Confirmed 3 times on the phone they could send a tech experienced with DUCTED mini splits. Tech shows up, and can't figure out why we would go to the crawl and explains minis are mounted on walls. I explain it is a DUCTED minisplit system. He goes to the crawl to look at it and turns to me stating "I've never seen one of these; had no idea they even existed. I'm certainly not qualified to work on it. Sorry." To his credit, his company never even charged for the service call, and later advised they don't work on the ducted mini's.
c. Although I'm a mid level DIY'er, I had never done more on an HVAC system than replace filters, replace a t-stat, pull and clean a squirrel cage fan, and replace an ignitor on a gas system. But since I was at a loss to get service after the above 2 episodes, I googled a bunch and fixed my system myself. I am lucky in that it was an error code I could find, and an issue that did not involve refrigerant.
If Mitsu wants to sell these multi head systems that are more complicated than traditional systems in the market, they need to do some significant work on having a network of service techs whom consumers are able to contact and hire, and who are competent and honest. Until something changes, I don't think I can in good conscience recommend anyone install a Mitsu system. Great equipment but you just can't get it serviced.
Where are you located?
SE US.
Thank you for your very thoughtful out thorough response!
2. If we can get our humidity inside stay around 40% while in cooling mode and with it blowing cold air, I will be good with that. My concern is if I take it out of drying mode, turn off the dehumidifiers and run it on cooling mode, our humidity will climb up anywhere from 60-70%. Thats just insane for our part of hot and dry California. We are hot as balls from May-September, sometimes even starting in April and ending in October. We are always in a drought because we hardly get any rain. So for this California girl, 50% humidity inside makes me feel like I can breathe and that is not a good feeling at all.
3. I completely agree- something changed. What is the question. There have been absolutely no changes in this area. We cook at the other end of the house, we have not installed a sauna LOL, we run the bathroom fans when we shower (which usually doesn't bring the humidity up too much)... there just haven't been any changes, OTHER than we started using the second cassette at the end of last summer. I dont recall ever feeling humid last year, but it is possible it was starting and we just didnt notice before we stopped using them for the winter. I do not know the answers to your questions about the the branch boxes and the evacuating the lines. I am going to copy and paste here what I told @DC_Contrarian about the charge of the system:
"My husband and I were talking last night about the charging of the unit. His best recollection is that he installed both cassettes at the same time and that our AC guy came out and charged them after that. We started using the bedroom one right away (three years ago in October) and then we started using the family room one at the end of last summer.
What I am wondering is...maybe something wasn't done with the second unit that needed to be. I know our tech was outside in the sun for hours doing the charging, but I dont recall the second cassette being hooked up at that time. My husband is sure it was."
If my husband is remembering correctly, the whole system was charged and brought online at the same time, we just didn't turn on the cassette for the family room until last summer since we were still building the room. When my husband comes back inside I will ask him about your questions re: branch, etc.
4. Our thermostats are wall mounted and they are not too terribly far from the cassettes. The family room one is about 8' away and the bedroom one is about 4' away. I am thinking they are wireless units since there are no wires in the wall and they run off batteries. Is that what you were asking? We are getting no errors codes at all. As far as what the t-stats think, everything is hunky dory. lol
5. Yes, this is what we are finding as well. Fingers crossed the certified guy who is supposed to come... some day... will come and is good! We completely sympathize with you and what you went through with your install!! My husband can build or fix just about anything, but I really dont want him to have to do it. He is a tree faller and works in the woods, 12-13 hrs day...up at 2 am to drive to work, etc. I just hate the idea of him working so hard outside the home to come and deal with this crap fest!
Other than this current issue, we have been really happy with our units. I have been really surprised, though, at how difficult it was to find someone to help us with service. I am a health insurance agent and I spend my entire day helping people. Even if it's out of my realm of expertise, I find the answers for them or at least point them in the right direction. I have been really stunned at how poorly I was treated by the last company.
If the unit in your bedroom worked fine with the family room unit off, it is highly possible the system was charged for one unit only. So when the family room unit was turned on, there is now insufficient charge in the system for the outdoor unit to serve both indoor units.
Based on your description, find the written calculations on lineset length, size and refrigerant weight and determine if they are for one or both units, and determine if both indoor units go to a branch box before going to the outdoor unit, and confirm the branch box is working properly (valves if any, controls, etc.) Confirm the controls for the indoor and outdoor unit are set for two indoor units.
I just came across this post when I was looking for my own post about a minisplit seemingly injecting humidity -- somehow -- into my son's room: https://www.greenbuildingadvisor.com/question/humid-room.
I posted it on the same day as you. How crazy is that?
Anyway, did you ever figure out what was going on? I cannot. When my son has his a/c on (Mitsubishi multi-head ductless minisplit, Massachusetts, 1940s cape-and-a-half) the humidity in his room skyrockets well past any other rooms -- even the ones that also have heads in them with the a/c turned on. And well past the outdoor humidity. Yesterday morning it was 86 percent in there, and it wasn't particularly humid at all outside. My installer/servicer had a tech come and clean the unit, test the condensate line, check the delta t, and gave up. He wouldn't return my phone calls, but wrote: "I don’t have an answer. What I do know is that if the air-conditioning is producing condensate water, that means it’s removing heat and humidity from the room. That water is humidity. It’s impossible that the air conditioning system is emanating humidity. "
Yeah, well, somehow this air conditioning system is emanating humidity, effectively. I suspect it may have something to do with the cellulose we had blown into the wall cavities a couple years back -- after the installation of the minisplits. This particular unit got clogged with cellulose, and though the servicer claims it's been thoroughly cleaned out, I suspect somehow it messed up the head, or continues to interfere with its operation.
It's driving me a little crazy. I walk into my son't room -- when, and only when, he has his a/c on -- and it feels clammy and wet, and the humidistat reads 79, or 84, or something. Meanwhile his sister's room next door will be 54 or something, at about the same temperature. I've considered vapor drive/condensation in the walls, basement moisture chimney effect, wet towels -- none of that appears to be present, relevant, whatever.
I'm having another technician come on Friday to look at the issue. I hope he's a little more thoughtful about troubleshooting.
But it would help to know -- did you figure out what was going on at your house?
You can't look at humidity in isolation from temperature. If you cool air without removing humidity the relative humidity rises -- because relative humidity is relative to temperature.
If it's 83F outside and 59% RH, if you cool that air to 72F without removing moisture the RH would be 86%. Without dehumidification the humidity inside will be higher than outside because human activity -- showering, cooking, sweating, breathing -- introduces humidity into the air.
Air at 72F and 86% RH has a dew point of 67F. If the coil in the air conditioner is not below that temperature, no dehumidification can take place. From your description it sounds like you've got a minisplit head in each bedroom. My suspicion would be that the head in that room is providing cooling, but not cold enough to provide dehumidification. Is the room on the shady side of the house? It's possible that the room just doesn't need very much cooling. It's also possible that the head is malfunctioning somehow.
When you measure humidity you need to measure temperature at the same time, one is useless without the other.
Regarding temperature: Your hypothetical scenario of an outside temperature of 86 or so and an inside temperature in the room in question of 70 or 72 is about right.
It is not the shady side of the house, but it is at night that this problem usually seems to happen. Typically: it's warm without a/c, maybe high 80s, so my son turns on his minisplit to 68-72 or so to sleep. In the morning it is 84 percent relative humidity in his room.
You are saying this is expected? It doesn't happen next door in his sister's room. It doesn't happen down the hall in my bedroom. His room feels clammy and wet immediately upon entering, and the humidistat supports that. No similar phenomenon appears to occur in other rooms that are a similar temperature.
But then you say it could be a problem with the unit -- what problem do you mean? My installer couldn't think of one...if you have any suggestions for what to look at I will have the new technician coming soon (now next week) look out for that.
Thanks for your thoughts.
Seems to me you are going to have to change your expectations as the equipment you own was never designed to deliver 40% humidity as you are expecting.
The air discharged from your AC ducts will be at over 95% humidity and no more than 25°below the room temp when mixed with the air in the rooms you might get down to 50% at best. That is just how it works and 999.99% of us find this reasonable.
There are a few places like museum and data centers that do buy special equipment and pay for the extra energy required to produce the cold dry air you are craving.
Maybe Bill will tell us a little about what needs to happen in data centers to keep them dry.
Walta
Hi Walta, you may be confusing me with the original poster. I would be ecstatic if my humidity were 50 percent. I am trying to figure out why the minisplit seems to raise it into the 70s or 8os.
What the original poster and I seem to have in common is that the minisplit in a particular room seems to raise the humidity way above what it is outside, and in the rest of the house.
Very interested in seeing what people did with this dilemma of high humidity. I am about a mile from the ocean in Santa Monica and I have a 8k Mitsubishi slim cassette in a fairly small bedroom. The outdoor humidity this morning was 88% And inside the bedroom, it had risen from 50% to 75% by morning. I just remodeled the place and I couldn’t have insulated the house more then I did… I have the best R value of windows as well.
I find it interesting that the slim cassette that I set at 68° raises the humidity level by 50% by morning. There is a dehumidification mode, but I can’t set the temperature and it lowers the overall temp to mid 60’s… It’s like a walk-in freezer in there.
I understand that that dust mites thrive in this kind of humidity. I need to get this under control because I’m allergic to them. Is a dehumidifier in my only option?