Minisplit is not dehumidifying. White lineset. Possible issues?

jchester404

We have 4 Mitsubishi heads, 1 per room. Been having a non-condensing/non-cooling issue in 1 bedroom. A tech came out and suspected a leak. He added 1lb 410a in the system when I was inside taking care of my kids. I did not approve of it, either way this remedied that unit. That unit is now working properly and is now condensing. HOWEVER, its not dehumidifying. The room is a constant 70-75% BUT cool. At first i was thinking the unit was too big (9k btu in a 12x12), but i have 2 other units in the same size room with no humidity issue. All rooms are used roughly the same. Same 2 sized windows in each room.

Faulty unit? Evap coil leak? How is it condensing but humidity won't drop?

System leak? When this was installed they used white lineset. Seems to be a lot of issues with this insulation creating an acidic environment inside the sheathing resulting in pitting/tunneling. Lines are in the crawlspace and theyre ALWAYS dripping. Original installers never sealed up the ends so inside insulation is exposed. Very bad.

Stressed. Any input on how to tackle all of this? Yes, ill get another tech out, but just doing research on my own as well. Its odd that its cooling AND condensing, while the room maintains 75% humidity. Only that room.


Thanks

pecmsg

The only way to know the proper refrigerant charge is to pull and weigh it. Then compare to the factory charge data. 

ratio

Why are the linesets in the crawlspace sweating? It sounds like you do have a leak (although it's possible that the initial charge wasn't right), but you may be looking at more than a low charge. Did the system ever control humidity in that room? Do you have humidity issues in the crawl space? Without expensive controls in place, humidity will move throughout the house once it's inside the envelope.

BTW, you can calculate the charge yourself. The Mitsubishi sizing software is available online at https://mylinkdrive.com/USA/Software/Engineering/Diamond_System_Builder/Diamond_System_Builder?product. You'll need the indooe & outdoor model numbers and lineset length (± a foot or so) & it'll tell you what it needs.

jchester404

I plan on measuring this weekend. The original tech wrote down how much he charged it with.

I've started having humidity issues in that particular room at the end of last summer. I was just about to edit my post with a few pictures of my lineset. ALL of it is sweating. As you can see in the pics they all have droplets of water on them (a bit hard to see). However, you'll see how tight all these zip ties are! Would this cause ALL of the line to sweat? Should I simply cut them and let them hang loose? Second, as you see in one of the pictures they never sealed the end of the insulation! What should I do here?

GGross

when were these installed?

jchester404

These were installed 5 years ago. Have no had any issues with anything, aside from inefficient cooling towards the end of last summer in the mentioned room. Didn't see it as a big deal, then started acting up this summer and realized it was something I had to take care of. Crawled under and noticed all of this.

Should I cut these zip ties? Should I seal those ends that have exposed insulation?

GGross

My gut feeling is that you are correct to be concerned about the lineset, I would seek a second opinion. I can't imagine someone adding a whole pound to a minisplit system without having a leak to show for it. As well the whole system should have been pulled down and weighed back in, at least for my mini splits throwing in a pound of refrigerant and calling it a day would be considered downright foolish and goes against every bit of training the factory offers

edit: to clarify I am not suggesting that you cut zip ties, or seal the leaky spots, call a different AC company to check the lines for leaks

5 years ago is right around when bad lineset issue started if I remember correctly, my local competitor got hit hard by that

jchester404

Yeah agreed.

What should I do about these zip ties? Simply cut them? And for now I should at least seal up those ends so bare insulation isn't showing. How should that be done?

GGross

@jchester404

Sorry I typed my response and then saw you had commented so I edited it. Don't mess with the zip ties or anything, call a different company to check the linesets for leaks

jchester404

Interesting OK. They don't seem to be serving any purpose only to keep the 2 lines together. They're not used to suspend them. They're all just so tight

GGross

@jchester404

If they are not holding them up at all it is probably fine to just cut them. My primary reasoning for saying not to do it is that if the lines themselves are leaky cutting the zip ties won't change anything.

jchester404

Wouldn't TIGHT insulation be the cause for at least the condensation build up on all the lines or no?

Sorry for jumping around on issues here - seems like I have a few of them ha.

ratio

The zip ties aren't all that bad, at least the ones in the pic. The bare copper is a bigger concern. How much of it is exposed? That, I'd repair. You can get insulation that's split (with a sealing flap) to fix it with, but if that's the brand that leaks, there's not much sense in fixing it.

jchester404

1. About an inch or so right before it goes in and out of the branch box (which is what you see in the pic. I feel like that should be sealed. This a concern?
2. Wouldn't the condensation/dripping on the insulation be caused by such tight compression on the insulation?

jchester404

update: I put the unit in question on dry mode, low fan, for a few hours. Made the room go all the way down to 50-51degrees but the humidity was still 70%! How is that possible?

ratio

Looks like quite a bit more than in inch or so in that pic. In any case, you shouldn't be able to see any copper, nor the flare nut. It should all be covered.

I use tape, not zip ties, to hold things together, but yours aren't near as tight as they can get. They're not having a significant impact on the R value of the insulation.

My guess is the dew point in your crawl space is high enough that the normal exterior temperature of the lineset insulation is allowing condensation on the jacket. That shouldn't be a big issue, however, because the outer jacket is also a vapor barrier that should keep the moisture off the copper. The exposed copper is certainly causing condensation that is wicking down the insulation. That's my concern, especially if you seem to have the lineset style that is susceptible to small leaks.

Again, the only way to verify the charge is to suck it all out & weigh it (with a good guesstimate of what's left in the hose to the recovery jug).

jchester404

I will definitely pull out and weigh. Just trying to figure things out in the meantime.

This condensation is really an issue as its pooling greatly along the whole path of every run line set. I need to do a full encapsulation. Looks like I'll have to clean up that exposed copper and buy some Armaflex pipe insulation. I guess I'll just butt it up next to my white insulation and tape with insulation tape, yes?

Lastly, how can that room's unit (on dry mode) get that room to 50deg but still only maintain 75% humidity? When I tested the air flow out it was hitting in the mid 30's. If it's an issue with the coil how would it blow that cool of air? I'm really confused.

mattmia2

Sounds like you're getting a ton of humidity from somewhere. Is the ground water higher than normal or a downspout broken and duping water where it gets in to the crawlspace floor or something like that?

I don't know if that insulation is open or closed cell.. Hopefully it is closed cell, but if it is open cell condensation in it will reduce its r value to close to nothing.

jchester404

Nope - my crawlspace is open. It's a nightmare. I'm doing full encapsulation in the fall. It's just weird how only 1 room is targeted

mattmia2

As far as the dehumidify function goes, you really need to compare wet bulb temps or dew point. Since 75 degree air can hold much more moisture than 50 degree air, 50 degree air at 70 percent rh contains a lot less moisture than 75 degree air with 70 percent rh. You may have a lot of solar gain in the other rooms that this room does not have so the load in those rooms is more. Are you using the same instrument to measure rh in each room? I have never seen 2 of those cheap humidity gauges with a needle agree with each other.

ChrisJ

mattmia2 said:

As far as the dehumidify function goes, you really need to compare wet bulb temps or dew point. Since 75 degree air can hold much more moisture than 50 degree air, 50 degree air at 70 percent rh contains a lot less moisture than 75 degree air with 70 percent rh. You may have a lot of solar gain in the other rooms that this room does not have so the load in those rooms is more. Are you using the same instrument to measure rh in each room? I have never seen 2 of those cheap humidity gauges with a needle agree with each other.

Even the typical digital ones aren't great.
I have a few in my house that are usually within 5% of each other but never agree. I consider them "good enough" though.

I recently installed AC at my bosses house and we went over there and his digital thermometer claimed 65% but there's no way. You can feel 65% and the house felt more like 40-50%. Cool and comfortable. That house is also very sealed and the evaporator was running very cold. I haven't checked it in a while but I'd expect a 23-25F drop across it due to how it's set up right now.

Point being both analog and digital humidity gauges tend to suck. I use them in my house, and watch them to give an idea of if the humidity is high or low, but the number it shows may not hold much water. For example, my thermostat typically shows 46-52% in the summer and I know that's normal. If that thermostat shows 55-60% something is likely wrong.

ChrisJ

@jchester404
What fan speeds are the heads set to?
Automatic, or a fixed speed? If you're running the fan too fast it may cool fine but the dehumidification will be pretty bad under most conditions.

jchester404

I'm using a cheap-o digital one as well as the reading on our separate dehumidifier machine. They're roughly the same.

So it got to 51 with 75% humidity which means dew point was 43. I'm reading what is a healthy RH. But I'm a bit confused. Shouldn't I be more concerned with the dew point, or no?

Been doing a bit a research and I think I'm just oversized here (9k in a 144sq/ft). The machine appears to be working, it removed water, but it's possible that it did it so quickly that the fan might simply be blowing back in moisture. Either way, I'm going to do some more testing like you all suggested. Will try a bit higher temp with fans set to low and see how it goes.

GGross

@jchester404

Generally the issue with mini splits not dehumidifying has to do with them being oversized. In your case 9k might be the smallest indoor unit available. However it is hooked to a multizone outdoor unit if I am reading this correctly, so you are still limited by the lowest range of the outdoor unit. I handle a different mini split brand, but they may be similar turndown ranges, our multi head ODU lowest capacity is 8400, so even though our IDU unit could modulate down to 1,000 the ODU can only go down to 8400 so it will need to operate the IDU at 8400.

If you are satisfied that there are no refrigerant leaks, you can go ahead and reinsulate the linesets where it is missing, this won't fix the humidity issue, but it needs to be done. It is possible that your mini split manufacturer may have a recommendation for how to alleviate some of the issue. Off the top of my head can you open a door or provide airflow to another room that maybe doesn't cool down all the way? something to add load to the space within reason.

Also, do you know the model number of the outdoor unit? this would tell you the minimum cooling range for that unit, which may help you in the quest to fix the problem

mattmia2

You said you had a dehumidifier, is that still removing moisture?

jchester404

mattmia2 said:

You said you had a dehumidifier, is that still removing moisture?

A separate dehumidifier and yes that is removing the moisture. Pretty much constantly runs when it's set to 55%

jchester404

GGross said:

@jchester404

Generally the issue with mini splits not dehumidifying has to do with them being oversized. In your case 9k might be the smallest indoor unit available. However it is hooked to a multizone outdoor unit if I am reading this correctly, so you are still limited by the lowest range of the outdoor unit. I handle a different mini split brand, but they may be similar turndown ranges, our multi head ODU lowest capacity is 8400, so even though our IDU unit could modulate down to 1,000 the ODU can only go down to 8400 so it will need to operate the IDU at 8400.

If you are satisfied that there are no refrigerant leaks, you can go ahead and reinsulate the linesets where it is missing, this won't fix the humidity issue, but it needs to be done. It is possible that your mini split manufacturer may have a recommendation for how to alleviate some of the issue. Off the top of my head can you open a door or provide airflow to another room that maybe doesn't cool down all the way? something to add load to the space within reason.

Also, do you know the model number of the outdoor unit? this would tell you the minimum cooling range for that unit, which may help you in the quest to fix the problem

Indoor units are MSZ-FH09NA. Outdoor Mxz-4C36NAHZ

I'm not confident that I'm leak free. Quite the opposite. In the beginning of the summer when we made the switch to AC mode one unit produced bits of rice-sized ice. This only lasted a week or so. Skip to a month or so after and I started having that non-cooling issue with the other unit. Signs of an under-changed system yes?

And yes I'm going to insulate the flare nuts and the exposed copper by the branch box. I went down to 2 local HVAC supply stores locally but they didn't have any insulation for 1/4 and 3/8. What brand do you recommend so I can order online?

pecmsg

A few years ago that type line set had all kinds of issues with leaks. 

GGross

@jchester404

According to a submittal I was able to find online that unit has a minimum capacity of 15,500 so the ODU will always cycle if only 1 IDU is calling.

For seamless insulation we usually use Armacell, and we generally use IMCOA split seam insulation. You will probably want to get some split seam insulation as your linesets are connected on both ends, though it would generally be proper to have seamless the full length of the lineset (seamless is generally more "rubbery" less "foamy" tighter fitting better for this purpose).

Personally I would worry more about finding out if you have a leak and making the proper repairs to that end first.

jchester404

Ah I was a bit confused by IDU and ODU. The outdoor unit goes into a branch box and then from there it's distributed out to 4 indoor units.

That's the plan. At least fix the exposed and then get a tech out. I'm looking at my outdoor unit and it shows what my pressures should be on the high and low side. You can't determine if it's under-charged or over-charged by those pressures?

I'm looking at K-Flex Pipe Insulation now. Bit confused - I need insulation for 1/4 pipe and 3/8 pipe. For example: https://www.supplyhouse.com/K-Flex-6RXLO048038-3-8-Pipe-O-D-x-1-2-Wall-Insul-Lock-DS-Overlap-Pipe-Insulation-6 . It says 3/8 OD but under the specs it says Application: 1/4. Not sure I understand.

edit: I'm dumb. Inner 1/4 will have a 3/8 OD

mattmia2

Do you see actual water condensing from the dehumidifier? I have a graveyard of 3 that all lost their refrigerant through what should have been solid copper tubing that I discovered had failed because they ran constantly.

GGross

@jchester404

Refrigeration pipe is generally discussed as the tubings outside diameter OD. So when the lineset says 3/8" it means 3/8" OD tube. If I were plumbing a house, or discussing any other pipe I would call it 1/4" tube, what is called "nominal size" or the inside diameter ID. 1/4" nominal size copper is 3/8" OD Copper comes with different wall thicknesses which is likely the reason we discuss the pipe in different applications by either its OD or ID

jchester404

mattmia2 said:

Do you see actual water condensing from the dehumidifier? I have a graveyard of 3 that all lost their refrigerant through what should have been solid copper tubing that I discovered had failed because they ran constantly.

I do yes

jchester404

GGross said:

@jchester404

Refrigeration pipe is generally discussed as the tubings outside diameter OD. So when the lineset says 3/8" it means 3/8" OD tube. If I were plumbing a house, or discussing any other pipe I would call it 1/4" tube, what is called "nominal size" or the inside diameter ID. 1/4" nominal size copper is 3/8" OD Copper comes with different wall thicknesses which is likely the reason we discuss the pipe in different applications by either its OD or ID

Gotcha. So for example, in this video he's describing how to calculate the needed additional refrigerant: https://www.youtube.com/watch?v=RiBjwQbpFe8 . He calls it 1/4 and 3/8 line. I have to assume it's the ID as it's referencing refrigerant that goes in the pipe. Therefore, I need 3/8 OD and 1/2 OD insulation for 1/4 and 3/8 lines, correct?

mattmia2

Refrigeration tubing is measured by the od. 3/8 and 1/4 soft copper tubing dont have a common hard copper pipe or iron pipe equivalent od.

EBEBRATT-Ed

If you're sweating the line set in the crawl space the refrigeration used to make those lines sweat is capacity lost at the evaporator coil. If the line set stays, I would reinsulate the whole thing with thicker insulation.

Every gallon of dripping water is probably 800 btus lost, like steam in reverse

jchester404

EBEBRATT-Ed said:

If you're sweating the line set in the crawl space the refrigeration used to make those lines sweat is capacity lost at the evaporator coil. If the line set stays, I would reinsulate the whole thing with thicker insulation. Every gallon of dripping water is probably 800 btus lost, like steam in reverse

I really think it's the temp differential between the insulation jacket and the air in my crawl space. I mean my crawl space is HUMID. That has to be a possibility right?

jchester404

mattmia2 said:

Refrigeration tubing is measured by the od. 3/8 and 1/4 soft copper tubing dont have a common hard copper pipe or iron pipe equivalent od.

So if Mitsu is saying 1/4 and 3/8 (as such in that video) they mean OD? If that's the case I can't find 1/4 insulation tubing any where

pecmsg

Any refrigeration supply house will carry it. 

If that crawl space is that bad 1/2” wall thickness may be required. 

Be prepared for sticker shock, insulation is more expensive then copper!

jchester404

Well I don't plan on replacing all of the insulation right now. Only the exposed parts until I can determine if there is a leak.

Is there special insulation that goes over flare nuts?

pedmec

just asking if i read that right. you are saying that the room temperature was 51 degrees and the rh is 75%?