All true in a standard system.
In a minisplit, it’s nigh impossible…
What Mini-Split did you use, and Why?
- Thread starter Lt.Dan
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In a minisplit, it’s nigh impossible…
In an automotive system, you can buy refrigerant mixed with a qty of oil to try and replace what likely leaked out from a leak… larger, or hermetic systems do not have oil sold with the refrigerant.
Oil is in the compressor sump, it does dissolve into the refrigerant as the system operates. If there is a superheat related issue, the refrigerant can flood the compressor crankcase, and get pumped into the evaporator, then when the compressor seizes, all he oil is left there, and the new compressor has its own oil fill, then TWICE the oil quantity for the system is in there, and it flushes back to the crankcase, overfilling the sump, creating its own issues.
RCinFLA
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There is no oil mixed in new refrigerant jugs. Just the refrigerant.
Oil is initially loaded by compressor manufacturer in sump of compressor. Compressor must remain corked up with slightly pressurized dry nitrogen gas until it is installed in unit.
New outside units are preloaded with oil and refrigerant. Compressor manufacturer supplies oil in compressor. Outside unit manufacturer pre-charges outside unit with refrigerant. Pre-load of refrigerant is typically good for 25 ft. lines to inside unit. If longer lines are used you have to add some more refrigerant. Install manual specifies how much refrigerant to add for additional line length beyond stock pre-load amount.
A system leak may cause oil to be lost from system. Looking for oil leaks is first step in exploring where refrigerant leak in system is at. Usually the amount of oil lost for a refrigerant system leak is not severe enough to require more oil be added to system.
In some cases of very long refrigerant lines between inside and outside units additional oil may need to be added to system.
The compressor oil sump reservoir quantity has a lot of margin.
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All very interesting. I noticed in the manuals there’s a formula for additional refrigerant but no mention of oil to be Added. Is this because of the “margin” in the sump?
another question…. For these mini splits that are “precharged” and diy friendly, is the line set precharged with refrigerant, or are they pre vacuumed?
Are you able to evacuate the system, and eliminate the double oil situation?
RCinFLA
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Yes, the sump reservoir often contains enough oil to handle the longest possible lines the compressor can handle with its pumping capacity. If lines are so long you need to add oil, then the lines are likely too long for the compressor to push the refrigerant through them with the power it has.
Oil dissolves in liquid state refrigerant but when vaporized in evaporator the oil drops out to mist droplets that must be pushed along by the vapor mass velocity. If lines are too long there may not be enough vapor velocity maintained to push the oil back to compressor.
Compressor determines the amount of oil ejected by its rotational speed. Once condenser liquifies refrigerate, the oil mixed in liquid refrigerant moves out very easy. It can end up getting trapped in evaporator or accumulator if there is not enough vapor velocity on return vapor line.
Any variable speed compressor system has to be careful of running at too low of speed, for too long of time, because at low speed the vapor velocity on return line is reduced potentially allowing oil to remain in evaporator or accumulator.
Most variable speed compressors have an accumulator next to compressor that helps hold a reserve of oil for slow speed run time that can be picked up by compressor.
The accumulator however makes traditional subcooling and superheat measurements for determining amount of refrigerant charge meaningless.
This means the only way to add refrigerant properly to a mini-split is to recover all remaining refrigerant in system and then load a weight measured amount of refrigerant into system. The service manual specifies the weight of proper refrigerant load. Just adding some refrigerant to a mini-split can easily result in an overcharged system that will damage compressor.
Because subcooling on a mini-split is meaningless, the manufacturer usually deletes the high pressure test port as it is not needed for subcooling measurements.
Another complication is when inside unit is significantly below the outside unit, like a four or five story condominium with outside unit on roof. 'P' traps on return line must be installed to allow return oil to momentarily get trapped in the 'P' traps to jack it up and help get it back to compressor. It is sort of like salmon swimming upstream with multiple moderate height dams along the river they can jump up over.
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Plum Crazy Rob
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I'm glad someone FINALLY explained this. Thx.
Thank you for explaining all of this. I always wondered why minisplits don't have a high side port.
No.
The only way to eliminate the issue is by replacing the evaporator coil, and flushing the lineset.
AlaskanNoob
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Just got a blower test done on our cabin (1.63 ACH at 50P) and we're getting ready to order a heat pump that will be run off our solar off grid. Thinking about buying a one ton Mitsubishi Hyper Heat. There aren't any installers around, we'd have to get one from Anchorage to make the trip but they're not trained on Mitsubishi so who knows how that would go. Not sure this is something we'd want to try to DIY ourselves given our lack of tools and knowledge. I did notice that they sell a pre-charged 25 foot line set, but I'm not sure that would really make it simple.
Anybody DIY a Mitsubishi Hyper Heat?
Also, would I be correct in thinking you'd want the shortest line set for the unit, or at least to keep as little of the line set outside the home so that it has less heat loss from the line during cold temps?
Anybody DIY a Mitsubishi Hyper Heat?
Also, would I be correct in thinking you'd want the shortest line set for the unit, or at least to keep as little of the line set outside the home so that it has less heat loss from the line during cold temps?
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The Mitsubishis need rock solid install... I wouldn't recommend a diy on that, at least not the lines...
Get a pro...
Get a pro...
Mr. Cool is DIY friendly.
AlaskanNoob
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Yeah, it definitely seems so from what I've seen. But I don't think it's going to deliver what we want at -10F.
AlaskanNoob
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That's what I figured. Unfortunately, if a pro doesn't have familiarity or training on the Mitsubishi units, I'm not sure if they will be pro enough. The complaints I've seen about these units online seem to all trace to a bad install or somebody installing differently than Mitsubishi requires.
Bob in Tucson
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Just this week, I installed a Mitsubishi 9k (MUZ-FS09NA outside unit, not a MUZ-FS09NAH -- the H indicates Hyper Heat) but had a pro connect and vacuum the lines and release the refrigerant. That means I had everything ready to go, so he was here for less than an hour.
For me, there were several advantages to this approach -- I got to do most of the installation plus I got a license number to include for the warranty. I have not registered it yet, but I'm hopeful it'll go when I do.
I don't think there was anything special he did and I imagine the Hyper Heat version is the same, though I don't know that for sure.
Not every tech is willing to do what this one did as there is more money to be made doing the full installation. Plus, if you use a Mitsubishi certified tech you would get a longer warranty.
For me, there were several advantages to this approach -- I got to do most of the installation plus I got a license number to include for the warranty. I have not registered it yet, but I'm hopeful it'll go when I do.
I don't think there was anything special he did and I imagine the Hyper Heat version is the same, though I don't know that for sure.
Not every tech is willing to do what this one did as there is more money to be made doing the full installation. Plus, if you use a Mitsubishi certified tech you would get a longer warranty.
Their literature says down to 5°F. But I think that just means it’s not very efficient below that. There’s a guy in Fargo that had Mr. Cool down below -20 Fahrenheit. Gree advertises down below -30 Fahrenheit. Have no idea if they really do very well that cold.
Olympus Hyper Heat | MRCOOL
Enhanced Heating Performance. The MRCOOL Olympus Hyper Heat - Single Zone | Energy Star Certified
mrcool.com
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I've installed them all.
Diy types certainly work, they frequently are low teir equipment.
Install skill is key, nothing is more important on an hvac install than attention to detail and a high skill at it.
That said, MANY "PRO" techs are gas and go seat ot the pants techs...
Keep in mind, when you source the equipment, YOU are the warranty company... sure installers like to source and mark up the equipment, but when a problem hits, especially in the first year of operation, the installer is on the hook to service and remedy the issue... not so if you do all the work, and they pump it down, and loose the refrigerant...
I've done both... I love a quick flare, flash and evac job.
I charge my hourly rate and the customer gets a great leak free no contamination line set job.
But when I do the entire job, I know it's right, and I warranty my work for 2 years.
Diy types certainly work, they frequently are low teir equipment.
Install skill is key, nothing is more important on an hvac install than attention to detail and a high skill at it.
That said, MANY "PRO" techs are gas and go seat ot the pants techs...
Keep in mind, when you source the equipment, YOU are the warranty company... sure installers like to source and mark up the equipment, but when a problem hits, especially in the first year of operation, the installer is on the hook to service and remedy the issue... not so if you do all the work, and they pump it down, and loose the refrigerant...
I've done both... I love a quick flare, flash and evac job.
I charge my hourly rate and the customer gets a great leak free no contamination line set job.
But when I do the entire job, I know it's right, and I warranty my work for 2 years.
ArthurEld
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It shows a $50 off coupon for me so $649. oh sorry, old post. 
AlaskanNoob
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On the off chance that we have any certified Mitsubishi heat pump installer types on this forum, send me a private message if you like salmon fishing, free air travel and nice off grid accommodations in exchange for a couple hours of work on a hyper heat unit...
Heh... round trip flight included?
Lt.Dan
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What if I lied and said I was, just for the trip?
RCinFLA
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Mitsubishi units also have electronic power factor correction for their inverter AC to HV DC power supply. An important consideration if running from a battery powered inverter or generator.
You won't find a power factor spec on most manufacturers' mini-split units. They can be as poor as 50-65% particularly on smaller btu units.
You won't find a power factor spec on most manufacturers' mini-split units. They can be as poor as 50-65% particularly on smaller btu units.
We have a Mitsubishi Hyper heat unit in a poorly insulated building we own, and it's amazingly good. Way better than our Daikin units, in my opinion. We had it installed by a local company that does a lot of Daikins but had never installed a Mitsubishi (or at least this crew hadn't), and it went fine. I would NOT DIY it. If you need to go that route, I'd look at a Mr. Cool. I think their newest units are rated to sub-zero temps, but admit I haven't checked that specifically.
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