Mini-Split Charging Procedures

[andmilair]

I had a Comfort-Aire 9,000 BTU unit installed by my HVAC contractor who services my Central unit. The unit came pre-charged for a 25-foot line set and I needed to add an additional 15 feet of line.

The Mini-Split was working great but now I noticed upon start-up the compressor would groan & vibrate but not start the compressor cycle. This would happen 2 or 3 times then the compressor would finally kick in and cold air would blow. I spoke with Comfort-Aire Tech support and he believes the system is overcharged. When I reviewed the bill, it included 4.5 lbs of Freon when the Tech said he should have only added 2 or 3 ounces. The Tech recommended that the unit be evacuated and the charge weighed to see how much was installed. When I spoke with my HVAC guy he said they do not use scales just gauges. Is he blowing smoke? Should I have this guy come back? What kind of damage has been done by running the unit overcharged for 2 – 3 months? How can I test the compressor to see what damage was caused. Any suggestions would be appreciated.

[Wild Leg]

You need to find a new contractor.

If he doesn't use scales, how did he determine 4.5 lbs was the amount to bill you for?

He's a hack.

[airworx]

most technitions use pressures to charge ac's. in reality pressure charging is vary inadequate and leads to overcharging.
if your evap coil has a txv then subcooling is used and if rfc is used then superheat and subcooling is used to charge your unit.

[Leo]

The mini splits I am familier with only use weighed in refrigerant. They don't even give you a chart to use temp/press readings like a conventional unit. Your guy needs to read the directions.

Leo

[hvacker]

A huge mistake many a/c techs make with minisplits is charging at the valves on the outside of the unit. While this is fine on most split systems it's all wrong on minisplits. A tech will add refrigearnt and have no effect on pressures so they keep adding and probably stop when they get worried.

The correct charging valves are inside the unit. This system uses a flooded coil like some walkin coolers use and can't be charged using the outside valves.

I think there should be a huge warning on these systems.

And ya if they don't use scales how did they know that they used 4 1/2# If they did use that much your almost overcharged for sure.

Most minisplits have good information on the web for downloading. It would be a start.

[RoBoTeq]

Originally posted by airworx
most technitions use pressures to charge ac's. in reality pressure charging is vary inadequate and leads to overcharging.
if your evap coil has a txv then subcooling is used and if rfc is used then superheat and subcooling is used to charge your unit.

I think I understand what you are stating, but am a bit confused over pressure charging being inadequate. I am going to assume you mean pressures alone, in which case I agree.

Of course it is true that charging by superheat for fixed metering and subcooling for TXV is the way to initially charge and both superheat and subcooling should be measured for troubleshooting any system, mini splits are measured a tad differently.

The metering device is on the outdoor unit of most mini splits. It is located at the service valve of the small line. For this reason, the small refrigerant line of mini splits must be insulated and never have a filter/drier installed.

Also; subcooling temperatures must be taken between the service valve and the outdoor unit, not on the small line.

[bmac]

FWIW, All the mini splits I have worked with, ( not that many) have said that you should not adjust the charge by any other method than weighing in.On a new install you would weigh in however many ounces you need for length of lineset. If you are low you would recover and weigh in new charge rather than adding by superheat or subcooling. I agree the contractor should have used scales and 4.5 lbs is probably more than the unit even came with. Usually a few ounces is all you would add depending on the length of the lines. Sounds like you're not going to get this fixed right without calling another contractor.

[mjk_na]

You can charge through:

1. Superheat (for capillary tube expansion device system)

2. Subcooling (for TXV system)

3. Or by weight (for any system). Check the recommended weightage with the manufacturer, or contractor.

Number 3 is preferred.

[Cousin Tony]

I think I understand what you are stating, but am a bit confused over pressure charging being inadequate. I am going to assume you mean pressures alone, in which case I agree.

Of course it is true that charging by superheat for fixed metering and subcooling for TXV is the way to initially charge and both superheat and subcooling should be measured for troubleshooting any system, mini splits are measured a tad differently.

The metering device is on the outdoor unit of most mini splits. It is located at the service valve of the small line. For this reason, the small refrigerant line of mini splits must be insulated and never have a filter/drier installed.

Also; subcooling temperatures must be taken between the service valve and the outdoor unit, not on the small line.

I don't know if your still around but i have a question if you are regarding the above. it has to do w/ the last sentence. i have a small 1 ton ductless mini split w/ a small leak ( i know i should fix it but its mine and i always have gas ) and i'm not going to fix it. I want to add gas only. no txv and metering device is in cond. unit. What do u mean by service valve and where at outdoor unit?

[beenthere]

Sorry, this is NOT a DIY site.

Thread closed.