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I just purchased an LG mini-split set:

18,000 BTU indoor unit https://www.supplyhouse.com/LG-LSN180HSV5-18000-BTU-Ductless-Standard-Multi-F-Air-Conditioner-Inverter-Heat-Pump-w-Built-In-WiFi-Indoor-Unit

7,000 BTU indoor unit https://www.supplyhouse.com/LG-LMN079HVT-7000-BTU-Ductless-Multi-F-Wall-Mounted-High-Efficiency-Air-Cond-Heat-Pump-Indoor-Unit-w-Built-In-WiFi

20,000 BTU outdoor unit https://www.supplyhouse.com/LG-LMU24CHV-20000-BTU-Multi-F-Inverter-Heat-Pump-Outdoor-Unit

The submittal sheet for the outdoor unit says that max piping length for the included refrigerant is 73.8ft. The actual wording is: "Piping Length (no add'l refrigerant, ft) 73.8".

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/LG-LMU24CHV-Submittal.pdf

Questions:

1) Since I am using two indoor units on one outdoor unit, does the max pipe length take in account both sets of pipes? For example if unit 1 has 50' of pipe, and unit 2 has 23.8' of pipe, will this be OK?

2) If I use less pipe than what is specified, will I have to drain off excess refrigerant? I assume not, but I just want to make sure

3) The suction line for 18000 BTU indoor unit is slightly larger than the suction line for the 7000 BTU indoor unit (1/2" vs 3/8"), but the liquid lines are the same diameter. Will this impact the maximum pipe length for the included refrigerant?

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You are asking questions about a system that requires EPA licensing and training. So it is somewhat off topic. Do you know the system needs to have a vacuum pulled on the lines? Most require 500um. A standard gauge set is normally used with a twin temp gauge after that to measure super heat and cooling, these values will be out of spec and more of the type of Freon your unit needs will have to be added. This can only be done by someone that has the appropriate 608 license for residential of which there are 3 most of us have all 3 or a universal license, even then an additional license is required to work on automobile/truck systems or a 609 license. Did you know there are rewards up to $10,000 for turning someone in for working on AC systems without a license, the fines go up to $25,000. So it is not a good idea to work on AC systems without knowledge and licensing. Note if your system did have a good vacuum level pulled prior to opening the system you have much larger evaporators than condenser (this is normal with mini splits) but the evaporators do require some of the charge also so you probably will need some additional fill to have the system properly charged, running a system low on Freon will shorten the compressor life especially on mini splits.

Added info 28 June 19 I thought I would make an update to this answer, in a recent training class I found out about some split systems that have precharged evaporators and line sets. The reason the training brought these up is they are a DIY install a bit more expensive up front but no license required. They are some what limited at this time (fixed line set lengths and single head) so you may find a coil next to the outdoor unit of ~15’ of line set that was not needed but it can not be shortened so the extra is left next to the outdoor unit. The training covered repair because since these units are diy and just “bolted together” there has been a fairly high failure rate. How are they DIY and why are they failing? They have self sealing connections at the connection point, the problem is that they suggest leak testing with bubble solution (this is how we find gross leaks that are really bad) professional leak detectors (not the 15-30$ internet specials) can detect leaks that are 1/1000th of bubble solution, so many of these DIY systems are failing at the 1-2 year from install point, they did suggest some liquid sealants to add to the threads of these joints and re charging if the DIY installer calls prior to damage to the compressor or moisture entering the system. So there are some DIY splits out there but be cautious as the extra cost up front is not much different from the same size system professionally installed and if you factor many splits have a 10 year warranty where the DIY have 90 days to 1 year ( not verified by me) the DIY may end up costing much more in the long run. I was unaware of these systems in the past but trying to help the stack exchange community thought I should provide this extra info that it may be possible to DIY a split system but I would suggest having it professionally leaked checked at the outdoor unit and the line set at the evaporator where it goes through the wall as these were the 2 main points of failure. With a well sealed system the higher quality split systems are expected to have a similar life span as a professionally installed system according to the training.

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