Posted: 7/24/2017 7:24:01 PM EDT
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I have had a two-zone Mitsu mini split system installed for a few months now. Today was the first day that it couldn't keep up with the set point. One unit (north) is blowing cold and the refrigerant lines are cold. The other unit (south) is blowing cool and the refrigerant lines are cool. If I turn off the north unit, the south unit becomes cold. When I turn the north unit back on, the south unit becomes cool again.
Any ideas? |
| I'm not certified in refrigeration, but I've helped co-workers install them. How many total feet of copper line set do you have? The unit comes pre charged with enough refrigerant for a certain number of feet depending on which model you have. If the total feet exceed that spec, the installer should have added the correct amount of refrigerant to the system to compensate. Or maybe you have a leak. |
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2 evaporators (indoor section) sharing 1 common condenser (outdoor section).....
Was it above 95 deg outside? Possibility that the unit is undersized for your indoor load. If both eveporators start blowing warm air when the other is off, then I may suspect a refrigerant leak. With all units running on a very hot day, compare the actual amperage of your condenser unit to the nameplate data. If it's within 5% of max amperage they are undersized. |
| Sigh. Mitsu customer support would be happy to give me some diamond contractor contacts, but couldn't tell me if the condenser would favor one unit over another if the refrigerant is low, or if both units would run the same. I'll have to keep looking on the Internet. |
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Sigh. Mitsu customer support would be happy to give me some diamond contractor contacts, but couldn't tell me if the condenser would favor one unit over another if the refrigerant is low, or if both units would run the same. I'll have to keep looking on the Internet. |
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they can't see what is going on that is on people like me the ac contractor, now if you had gages, electronic thermometers and some meters along with the skill to do it that would be another thing. the installer should come back under warranty |
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Sigh. Mitsu customer support would be happy to give me some diamond contractor contacts, but couldn't tell me if the condenser would favor one unit over another if the refrigerant is low, or if both units would run the same. I'll have to keep looking on the Internet. If you do not have the knowledge, that's fine, call a contractor who can help you. It really isn't that difficult. |
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Brother's FIL sent someone out for the initial install. I installed the units and ran the lines. I connected the wires, he connected the lines....backwards. I realized that the next day and swapped the wires. He noticed a damaged flare on one of the line sets but did not have flaring tools so he flared it with pliers. It ended up leaking so he came back with flaring tools and redid the flare, pressure tested (albeit very quickly), and then recharged. It held pressure and he got a good vacuum. The change in performance was from one day to the next. A leak, unless it developed yesterday, would have been more gradual.
I understand air conditioners very well. What I don't understand is how the condensing unit runs selective control on multiple evaporator units. I have a very simple question. If a multi-zone system is low on charge, will both units run similarly or will one unit be favored? If it is a matter of a simple on off valve to each unit, then they should run similarly. If the refrigerant flow is being controlled, I have no way to determine what the unit is doing. I know that the problem must be on the condenser side because either unit is capable of blowing cold air. I will also bring home a thermometer tonight so I can get the outlet temps with north only, south only, and both on. What makes this process more difficult is that I opted for the Kumo Cloud WITHOUT thermostat so I lack the normal controls/diagnostics that a mini-split system would have. I need to buy remotes... The Kumo cloud sucks. The app is very limited, it won't allow me to change fan speed anymore, and it forgets or makes up program settings. |
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Ive been both a tech and engineer in the field for over 30 years. I have selected and been a manufacturers rep for mini splits as well. Now for the REAL answer.
You are beyond help. There are at least 87 things wrong with your last few statements. I'm outa here......... |
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It forgets or makes up program settings. I do similar to you, OP. I physically install everything myself and my AC guy comes and does all the lineset connections and freon work. I am waiting for him to complete an install now. I tried a Daikin unit this time around. |
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One simple question. You've been a tech for 30 years and you can't answer it. You are so awesome I almost peed myself. Warm sticky mess..... yuck. Maybe your brother in laws father in law will bring his 60deg flaring tool to assist the pliers. Never mind, there's an App for that 
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Flared with pliers? Switched lines? I think you have install issues.
These units use Puron (r410) and run at high pressure. The connections are critical and need to be done with the right tools and properly torqued or you will have leaks. The unit is precharged with enough puron to handle a pretty long line set. That said from what you have provided: 1.) check for leaks 2.) did you install the correct sized suction and liquid lines? Are they hooked up to the correct fittings on the units? 3.) Was the system properly evacuated to vacuum before charging? |
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My Mitsubishi unit does the same thing. I don't use an app to control it, but even with the traditional controller remote the unit will adjust settings on it's own. My installer and Mitsubishi rep I talked to think I am crazy, but I promise it happens. The unit functions flawlessly otherwise. I do similar to you, OP. I physically install everything myself and my AC guy comes and does all the lineset connections and freon work. I am waiting for him to complete an install now. I tried a Daikin unit this time around. Instead we have antiquated diagnostics so 30 year A/C techs can continue to change $100+ dollars per hour. |
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Flared with pliers? Switched lines? I think you have install issues. These units use Puron (r410) and run at high pressure. The connections are critical and need to be done with the right tools and properly torqued or you will have leaks. The unit is precharged with enough puron to handle a pretty long line set. That said from what you have provided: 1.) check for leaks 2.) did you install the correct sized suction and liquid lines? Are they hooked up to the correct fittings on the units? 3.) Was the system properly evacuated to vacuum before charging? 2. The supply lines were size from the dealer. They are hooked up correctly. The unit worked awesome until yesterday. Nothing changed in the configuration before then. 3. It was pressurized with N2 and then vacuumed down, but I don't know to what level. He said that it wouldn't get that low if it had a leak. I would have liked more time to monitor for leaks, but it was getting dark and it was a call back so he didn't want to stick around long. |
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Brother's FIL sent someone out for the initial install. I installed the units and ran the lines. I connected the wires, he connected the lines....backwards. I realized that the next day and swapped the wires. He noticed a damaged flare on one of the line sets but did not have flaring tools so he flared it with pliers. It ended up leaking so he came back with flaring tools and redid the flare, pressure tested (albeit very quickly), and then recharged. It held pressure and he got a good vacuum. The change in performance was from one day to the next. A leak, unless it developed yesterday, would have been more gradual. I understand air conditioners very well. What I don't understand is how the condensing unit runs selective control on multiple evaporator units. I have a very simple question. If a multi-zone system is low on charge, will both units run similarly or will one unit be favored? If it is a matter of a simple on off valve to each unit, then they should run similarly. If the refrigerant flow is being controlled, I have no way to determine what the unit is doing. I know that the problem must be on the condenser side because either unit is capable of blowing cold air. I will also bring home a thermometer tonight so I can get the outlet temps with north only, south only, and both on. What makes this process more difficult is that I opted for the Kumo Cloud WITHOUT thermostat so I lack the normal controls/diagnostics that a mini-split system would have. I need to buy remotes... The Kumo cloud sucks. The app is very limited, it won't allow me to change fan speed anymore, and it forgets or makes up program settings. -No specific details on pressure test or vacuum -For the techs reading, any bets on how torqued the flares are right now? -Use an app to diagnose problems instead of proper tools -You say you understand air conditioners very well. -Frustrated because arfcom isn't fixing this for you fast enough Did I miss anything? |
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-Flared with pliers -No specific details on pressure test or vacuum -For the techs reading, any bets on how torqued the flares are right now? -Use an app to diagnose problems instead of proper tools -You say you understand air conditioners very well. -Frustrated because arfcom isn't fixing this for you fast enough Did I miss anything? > 100 ambient has zero effect on the system. |
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Don't forget the load calc, cause we know that > 100 ambient has zero effect on the system. eComfort.com did the load calc. Its 2.5 tons on a 1346 sq foot building with two 3x3 windows and ~R7 closed cell spray foam + R19 rolls on the walls and roof. 12 foot ceilings. I don't have specs on pressure and vacuum, but I watched them in process. I don't need arfcom to solve the problem. I just want to know why one unit was cold and the other one wasn't. I am trying to understand the relationship between the evaporators. That is the fundamental question. If the system is undersized OR low on freon, how would the condenser respond? The refrigerant lines going to the cold unit are colder than those to and from the warmer unit. Why are the refrigerant lines different temperatures? I don't need fucking load calcs. That's all I want to know. I'm sorry for the frustration, but it seems you guys want to berate me and the installer without answering the fundamental question. I did have some issue with his install practices... He used one wrench instead of two to tighten lines. He's gonna shear one one day, but I assume he's been doing this forever and I'm not going to tell him how to do his job. On the initial pressure test the only leak we found was on a connection I made on the evaporator so I tightened it more and the leak stopped. I was using two wrenches. Back to the fundamental question. I should have left out all of the honest details and maybe we could focus on the correct issue here. |
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well besides from a questionable install and possible warranty issues, the condenser itself just pumps refrigerant, it does not decide which head gets the refrigerant at which time, it gets a command from a unit for refrigerant opens a valve, the TXV detrimines how much refrigerant is need to flow to maintain coil temperature through the use of sensors and controls in the unit's EFC and ETC, the compressor ramps up or slows down accordingly.
you either have a leak or you have debris stuck in a valve because the installer did not know what he is doing. you may find that you have voided the warranty because you did not have a licensed and trained contractor installed it. you probably will not like this answer, but you should have hired a pro to install it |
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well besides from a questionable install and possible warranty issues, the condenser itself just pumps refrigerant, it does not decide which head gets the refrigerant at which time, it gets a command from a unit for refrigerant opens a valve, the TXV detrimines how much refrigerant is need to flow to maintain coil temperature through the use of sensors and controls in the unit's EFC and ETC, the compressor ramps up or slows down accordingly. you either have a leak or you have debris stuck in a valve because the installer did not know what he is doing. you may find that you have voided the warranty because you did not have a licensed and trained contractor installed it. you probably will not like this answer, but you should have hired a pro to install it Especially come warranty time. |
| Well the temp it holds depending on the outside temp is sort of irrelevant, the sun could be on that room one day and not the next which would increase the load for that room. Also for simplicity, if one run is 20 feet and one is 50 feet it will favor the shorter run because it will get colder refrigerant to the endpoint because of thermodynamics. If one run is longer than the manufacturer suggests it may also not have enough pressure to get it to that end point while simultaneously have the other side wide open. Also the systems are charged for a certain total length of line if you exceed that you need more refrigerant. If I bought a new fancy system and someone wanted to make a flare on a high pressure connection with needle nose pliers id say nah nevermind ill call someone competent. Leak down tests and vacuum is recommended on these high pressure systems for 24 hours under vacuum to check for leaks, not "quick". |
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Both evaps are identical distance from condensor. 35 ft. South wall gets more sun obviously, but the "room" is a barn that we made livable. Only the bathroom has a ceiling. You can see both evaps from anywhere. Both units normally run within a degree of each other inlet side, but yesterday I noticed a difference in outlet air.
If debris was in the expansion valve of the questionable evap, why does it blow cold when I turn the other unit off? I may also want to check for a kink in the high side line near the condenser where it was bent to fit. The high side copper lines seem extremely thin. |
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35ft? What model is this? 25 ft is the typical limit. After that you need to add refrigerant. Check the install manual.
If your connections were not properly cut, debuted, flared, and torqued they will leak. From what you have said it's pretty much guaranteed you have poor connections and you probably have a longer line set than the unit is rated for. Both of these issues mean you are low on r410. Bring in a tech who knows what they are doing to fix the problems. |
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He charged per the pressures. The side of the units says it is precharged for up to 9X feet of lines. I will check the connections with soapy solution today, and there was one bend I made in the lines where it felt like it gave and I need to check it but its hidden under insulation. I'll have to cut the insulation so I just bought tape and extra insulation during lunch so I can patch it up after I look.
I think the model is a MXZ-3C30NA2 which can handle a maximum of 230 ft of lines. |
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You are correct. That unit can handle a lot of line.
Have a certified tech pressure test it and run leak checks. If it used to work but has stopped loss of puron is most likely the problem (hopefully you don't have clogged valves). I have had a smaller 2 zone unit for about 4 years and they are very effective and reliable. |
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Both evaps are identical distance from condensor. 35 ft. South wall gets more sun obviously, but the "room" is a barn that we made livable. Only the bathroom has a ceiling. You can see both evaps from anywhere. Both units normally run within a degree of each other inlet side, but yesterday I noticed a difference in outlet air. If debris was in the expansion valve of the questionable evap, why does it blow cold when I turn the other unit off? I may also want to check for a kink in the high side line near the condenser where it was bent to fit. The high side copper lines seem extremely thin. |
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This is odd, and just reinforces my suspicion that something is wrong and it isn't the mistakes made during the install...unless it is #1 below.
It is 100°F and partly cloudy right now. BOTH units are blowing cold. The set point is 76, and the thermometer I brought home says 74-75 inlet and 54-56 outlet for BOTH units. Why was one unit not working properly the other day? I can't imagine anything being able to change that much except for: 1. Particles flowing in the freon that somehow got caught in the expansion valve and subsequently broke free. I don't know that this system has a filter like a normal split unit has brazed near the condensing unit. 2. The condensing unit wasn't sending freon or was sending too little freon somehow to the suspect unit. It can't be size. It can't be charge. It can't be weather. It can't be a kinked refrigerant line. |
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You stated no cieling in your "barn". This means the units are pulling the hottest air in the roof and trying to cool it......other issues aside you need a cieling and insulation above it to properly cool this space. On a cool day I'm sure it works just fine. Galvalume roof panels Rhino something water barrier 5/8" sheathing 1" closed-cell spray foam sprayed to the under side of the plywood and around the purlin except for the bottom face of the purlin. -~R7 23" R-19 fiberglass rolls pushed into the 24" on center purlin spacing. 1/2" R MAXX poly board, silver side down, sheet metal screwed to the bottom face of the purlin which is the visible ceiling. The r-value of the ceiling (and walls) is around R28 or so. This is temporary (3-5) years living space for a family of 4 until we build a traditional house. I've attached a picture of the not 100% complete evaporator. Traditionally the entire unit other than the grill would be above the ceiling, but this wouldn't fit up there and it would be too hot anyway. I didn't want a drop ceiling because this will be a workshop one day for tractor, vehicles, etc. Attached File |