The best way to find a leak is to pressure up the refrigerant lines and spray VERY soapy water on any fitting you see.
Also physically check the lines to look and feel for any possible defect.
Vacuum won't bring mini-split line set to minus 30
- Thread starter HowshouldIknow
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Also physically check the lines to look and feel for any possible defect.
shopman
Solar Enthusiast
First, pick up a squirt bottle of Big Blue leak detector. Then, pressurize the system with dry nitrogen to around 200psi and spray some Big Blue on all your connections to visualize the leak. If you can't pull a vacuum beyond -15inHg, you have a major leak that will most likely be audible once pressurized with nitrogen. I always remove the compression fittings on mini splits and swage/ braze the line set instead because compression fittings like to leak down the road.
If you don't have the tools or knowledge to do what I described above, please hire a professional to complete the installation.
If you don't have the tools or knowledge to do what I described above, please hire a professional to complete the installation.
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Plum Crazy Rob
Solar Enthusiast
Deleted, exactly what Shopman said.
Checkthisout
Solar Wizard
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What's the backyard way of leak-checking?
Compressed air, yes? Nitrogen isn't hard to come by but having to go down and get all that when one could just charge it up with air for backyard shadetree purposes.
To be honest, I have no idea how these work. Don't they come pre-dosed with refrigerant that the user lets into the system somehow? He doesn't have to get a bottle and charge the system up right? In our state you can't even DIY that anymore.
Compressed air, yes? Nitrogen isn't hard to come by but having to go down and get all that when one could just charge it up with air for backyard shadetree purposes.
To be honest, I have no idea how these work. Don't they come pre-dosed with refrigerant that the user lets into the system somehow? He doesn't have to get a bottle and charge the system up right? In our state you can't even DIY that anymore.
42OhmsPA
What's in a title?
I wonder if this would build enough pressure to find the leak? https://www.pioneerminisplit.com/pr...ng-kit-for-mini-split-air-conditioning-system
I also wonder if the OP needs new oil in the vacuum pump.
wpns
Solar Joules are catch and release
Most air compressors produce pretty humid air, which is really bad for HVAC compressors. By the time you get a nitrogen tank and get it filled you might as well call a pro, not sure if there's a rental market for tanks, but it sounds like an administrative nightmare.
Most splits come with the compressor (outdoor) section precharged with refrigerant.
Some systems come with precharged linesets and evaporator (indoor) sections, but that adds significantly to the cost and means you can't shorten the lines, you must coil the excess up (usually under the compressor/condensor unit).
The usual compromise is that you get the gauge set and the vacuum pump and pump the lines and evaporator down to a vacuum before releasing the refrigerant from the compressor section. If you have a leak like the OP, then you have to find it.
Plum Crazy Rob
Solar Enthusiast
Nitrogen tank rental was recently (Nov '23??) around $90 filled at Airgas, plus $35 for an Amazon regulator. If you can provide a current inspection date tank, fill was like $14 or such. Iffy for one unit, but for multiples it's a no brainer... 
42OhmsPA
What's in a title?
Edit - pursue at your own risk and read the reviews, some state no DOT stamp.Nitrogen tank rental was recently (Nov '23??) around $90 filled at Airgas, plus $35 for an Amazon regulator. If you can provide a current inspection date tank, fill was like $14 or such. Iffy for one unit, but for multiples it's a no brainer...
No idea if these are legit but those prices almost make it seem worth it to buy one.
New 20 cu ft Steel Nitrogen Cylinder with CGA580 Valve https://a.co/d/c5Ch5Nw
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hwy17
Anti-Solar Enthusiast
I pressurize with a propane tank lol.
But I'd also be willing to do it with compressed air, as long as it's from a decent tank compressor that doesn't spit water. There's all that hoopla about introducing moisture into the system, but I don't buy it - The linesets come with inside exposed to ambient moisture in the first place, and the vacuum pump removes moisture, just let it run for 30 minutes to be sure.
No disrespect to other people who do still want to be moisture cautious, if you have Nitrogen that's obviously better.
wpns
Solar Joules are catch and release
Reviews include:
/* Don't be fooled these are not stamped with DOT and can not be filled. Buyer beware */
42OhmsPA
What's in a title?
Post edited.
I have no problem using air to pressure up a line set if that's all you have , provided you pull a deep vacuum afterwards.
But you DO NOT EVER want to put water in your lines.
Nitrogen is the best method, it you have it.
When I started in the HVAC world, we just used refrigerant to blow the lines out, leak test the lines, kill fire ants, and anything else needed.
Checkthisout
Solar Wizard
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This would be my take. I do automotive a/c work all the time ans have no trouble finding leaks using various methods.
Home HVAC and refrigeration don't seem much different.
A little compressed air shouldn't hurt and you don't need much PSI to find the leak.
Some soapy water and good to go.
After repair just pull vacuum for a couple hours to boil the humidity out and I would think that would be good?
Especially since I'm sure the desiccant is probably still sealed in with the refrigerant charge (making some assumptions here).
These mechanical gauges are crap, believe me. You need a micron gauge to really get useful readings, e.g. Bluvac+ micro. Also quality of the hoses and the other connectors used (valve in between?) will deeply influence your vacuum.
Given the above, if you use good quality equipment: if you cannot pull close to the capacity of your pump after pulling vacuum for more than 30 mnutes (on mini split) it means 2 things:
1. either you have a small leak
2. you have moisture in the system
for (2) you can try pulling longer and flush the system with dry(!) nitrogen.
Otherwise for (1) you can also do a pressure test: put pressure close to the max pressure of the system (usually something around 400-500psi, read the number plate, do NOT use air!), then go search for leaks with something like Cal-blue.
Given the above, if you use good quality equipment: if you cannot pull close to the capacity of your pump after pulling vacuum for more than 30 mnutes (on mini split) it means 2 things:
1. either you have a small leak
2. you have moisture in the system
for (2) you can try pulling longer and flush the system with dry(!) nitrogen.
Otherwise for (1) you can also do a pressure test: put pressure close to the max pressure of the system (usually something around 400-500psi, read the number plate, do NOT use air!), then go search for leaks with something like Cal-blue.
you can use air but only on the lineset to indoor unit with the valves closed (before refrigerant is released). Otherwise you contaminate the oil!
Before you ever connect a vacuum pump, you need to test for leak down with dry gas of some type. Welding gas, helium, CO2, whatever. Using compressed air is a bad idea, because humidity under pressure will bond with the copper lines themselves. You can remove the moisture, but it is difficult, requires multiple dry nitrogen purge/pressure/purge cycles, with vacuum pump oil change between each pull…
ESPECIALLY with a minisplit that has no desiccant dryer installed. And no, you can’t install a liquid dryer in the system, because, the lines do not have liquid flowing through them… BOTH lines are gas lines.
Minisplits are difficult to evacuate properly. Most only have a single port to evacuate, or charge through.
It is good you have a vacuum pump, but no, the retard section of the compound gauge is NOT sufficient to test for a good vacuum.
At 29.9inHg (the lowest pressure a vacuum gauge can report on earth) There are 10,000 microns of pressure still on the system… you need a micron gauge to report what the lines are evacuated to. And it needs to pull down to 500microns, and hold before you are sure there is no leak, or moisture in the system.
With a perfect leak free lineset, you will pull down to 500 microns in about 20 minutes. With a leaking line, you may never reach 500, and it’ll rise RAPIDLY over 1100 when the valves are closed.
Proper evacuation of a minisplit lineset instructions call for a triple vac/purge/vac to be considered acceptable.
ESPECIALLY with a minisplit that has no desiccant dryer installed. And no, you can’t install a liquid dryer in the system, because, the lines do not have liquid flowing through them… BOTH lines are gas lines.
Minisplits are difficult to evacuate properly. Most only have a single port to evacuate, or charge through.
It is good you have a vacuum pump, but no, the retard section of the compound gauge is NOT sufficient to test for a good vacuum.
At 29.9inHg (the lowest pressure a vacuum gauge can report on earth) There are 10,000 microns of pressure still on the system… you need a micron gauge to report what the lines are evacuated to. And it needs to pull down to 500microns, and hold before you are sure there is no leak, or moisture in the system.
With a perfect leak free lineset, you will pull down to 500 microns in about 20 minutes. With a leaking line, you may never reach 500, and it’ll rise RAPIDLY over 1100 when the valves are closed.
Proper evacuation of a minisplit lineset instructions call for a triple vac/purge/vac to be considered acceptable.
Some good info on here. Lots of people don't have the best tools to setup mini splits but they do what they can. I would add, if someone is investing in the right gear, pick up a core depressor so you can isolate your gear without re-introducing air into the system when you disconnect. They are cheap.
If you can't invest in a micron gauge, there are round about ways to see residual moisture if you let the system sit after pulling a vacuum. You will see the gauge partial move, but not necessarily completely to zero if its a small amount and depending on ambient temp. It may go down to atmosphere. Pull again and recheck. Repeated drops to atmosphere is a leak. Be mindfull of how your gauges flow so you can adjust your valves to isolate the gauge to the system side. Use physics as your gauge...or yea, pick up a nice micron meter. I have 3 I have picked up watching for deals in the local adds for decent prices.
If you can't invest in a micron gauge, there are round about ways to see residual moisture if you let the system sit after pulling a vacuum. You will see the gauge partial move, but not necessarily completely to zero if its a small amount and depending on ambient temp. It may go down to atmosphere. Pull again and recheck. Repeated drops to atmosphere is a leak. Be mindfull of how your gauges flow so you can adjust your valves to isolate the gauge to the system side. Use physics as your gauge...or yea, pick up a nice micron meter. I have 3 I have picked up watching for deals in the local adds for decent prices.
Look...
An gauge indicated leak under vacuum is a HUGE leak.
There is only around 15psi difference between pure vacuum and atmospheric pressure. To see a slow leak under vacuum you need a micron gauge, and vacuum rated hoses.
Test for a leak under PRESSURE. With a dry gas.
Period.
Anything else is just hoping you didnt leave a fitting loose... dont bother.
He has not opened the valves.
He cannot get the line set to pull a good vacuum.
Edit: And my post stated for the line set.
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Partimewages
Solar Addict
Pulling a vacuum is not a replacement for finding a leak with a pressure test PERIOD!
This is the only right way. Other ways you will think are successful until one day your system fails. It will always fail on the hottest or coldest day of the year according to Murphy!
This is the only right way. Other ways you will think are successful until one day your system fails. It will always fail on the hottest or coldest day of the year according to Murphy!
hwy17
Anti-Solar Enthusiast
I believe mini splits actually don't have any.
usually pulling vacuum down to 50 micron, then re-testing for leaks after you release the refrigerant is enough. Good vacuum is good enough for me to pressurize it with refrigerant, then look for micro leaks if any. Of course, if you have nitrogen it you can add this additional step and test for leaks
btw there 2 types of leaks: some manifest under vacuum, some under high pressure...
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