Hi, I have a couple of mini split ac's and am having some issues.

One works fine for about 10-30 minutes and then just turns off. Fan stops but it puts out cold air when it runs. This one is a bondaire r22 unit.

I have another 33,500 BTU dual zone mitsu mr slim 17+17. This unit doesn't cool when its cold outside. If its hot, it works fine, if its cold, it won't cool. I called mitsu and they seemed to think it was undercharged. Any ideas? What should the charge be? It's a r410a unit.

Thanks

Mini splits are in a world of there own. You almost have to weigh in the charge instead of using a pressure temp chart. You need to find the component that is causing the one unit to stop running and I suggest you call a repair person well versed in mini splits for the other one suspected of being undercharged.

Sorry I can be of no further assistance on this subject since my knowledge of these type of units is limited. I have probably worked on 20 of them over these short years and each manufacturer is a bit different on there controls/compressor type/refrigerant/and charging style because of the use of different style line sets and restrictors (metering devices).

Thanks for the reply. How do I find the component that is causing it to turn off?

I agree, I think the mitsu is undercharged. I called mitsu and they said that those units are designed to cool at full capacity down to 14deg F outside temp. if it gets around 55 it doesn't work as well.

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Originally Posted by hvac1000

Mini splits are in a world of there own. You almost have to weigh in the charge instead of using a pressure temp chart. You need to find the component that is causing the one unit to stop running and I suggest you call a repair person well versed in mini splits for the other one suspected of being undercharged.

Sorry I can be of no further assistance on this subject since my knowledge of these type of units is limited. I have probably worked on 20 of them over these short years and each manufacturer is a bit different on there controls/compressor type/refrigerant/and charging style because of the use of different style line sets and restrictors (metering devices).

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You will have to catch the unit in the act. You will also need a meter to quickly test to see where the power/low voltage drops out. You might also ask the factory if they have any known defaults that will cause the cut out problem.

We have a Mr. Slim at a local hospital that we work on and almost anytime it gets under 40 degrees for any long period we have to wrap the outdoor coil with plastic to keep the head pressures up, it's in a area that gets really bad wind. Be careful they run really odd pressures you MUST weigh the charge in, I'd get someone that knows a little about them because they are so expensive and over chargeing may result in having to replace it.