Which "test&purge" strategy for a pre charged Mini Split install ?

[maxki]

I just installed a mini split (Senville 9k btu) , and I'm at the stage where refrigerant lines need to be connected, tested and vacummed.

The initial plan was to call a local HVAC technician to do this crucial step, but it turns out no HVAC contractor in my town wants to do it !

I have called 7 so far, all have refused, and a few have politely told me that they consider self installers as "competition".

From what I understand (based on the price they sell units) they make way more profit on selling units, than they make from selling their expertise.

In this economy, being a sales middlemen is more lucrative than selling expertise.

Being a DiY and having decent understanding of thermodynamics (I have a scientific background and enjoy reading about this stuff), I'm actually looking forward to doing this myself (I have an excuse for going the DiY way ;-)).

The main reasons I wanted to hire a certified HVAC guy, was to not void my warranty, and a reluctance to buy tools I will only use once per 15 years.

I am now trying to choose between the 3 options (from quick & dirty to "state of the art").

Note: the unit came pre charged with r410a :

1. "quick & dirty"

• purge with low resolution gauges (the cheap ones that only measure in PSI)
• shraded valve not removed while vacuuming

2. "better"

• purge using a micron gauge, with shrader valve removed

3. "best"

• nitrogen pressure test
• vacuum with micron gauche

I've already bought the equipment for option #1, and I'm considering getting the extra tools for #2 (micron gauge and core remover tool), but hesitant.

For option #3, I'll need to buy a nitrogen regulator, rent a nitrogen bottle.


My current thinking is:

i) After a visual inspection of the flares on the refrigerant lines, the flares look very well made (nice flat surfaces, proper dimensions, angle, etc), and given that I will use nylog, and a somewhat decent torque wrench, the probability of failing the 4 connections seems low.


ii). Given that the unit is pre charged, and that the wall unit is still pressurised, the only humidity in the loop will be in the air inside the 16 feet copper lines. Leaks on the wall unit can be excluded, or rather, I will detect it when I depressurise the connectors. Leaks in the pre charged outdoor unit is also unlikely, it's a new unit, factory tested, etc.

I'm thinking that #3 is probably overkill in my situation, I'm rather confident about connecting 4 flares, and gross errors will show on the vacuum leakage test.


I'm mostly leaning towards option #1 or #2 :

Pros for #1:

• I can do it right now !
• If I leave the pump on, *after* I reach -30 on the gauge, I have "reasonable assurance" that the lines (and indoor unit) will be "decently" purged.
• no micron gauge, and core remover tool to buy ($300, going for low budget tools kind of defeats the purpose of this extra step)

Cons for #1:

• I have no idea of how "Reasonable assurance" translates into probabilities, is it 0.99%, or is it more like 0.80% ?

Option #2 seems like a good middle ground, and , it also has the extra benefit that I can lend it to "do it yourselfers" in my town. I will gladly lend them for free (to those who will convince me they know what they're doing), just for the sake of going against, the sad reality that "expertise industry" is turning into sales industry.

I'm not blaming them, it's a general tendency (systemic issue) of our "economic climate", in which being a "salesmen" is much more rewarded than being a maker. In this climate, a highly skilled technician that only sells his expertise, will get eaten by an MBA that sits on a desk and talks on the phone all day.

 

[like2wheel]

Subscribed

 

[ching0n]

I did nitrogen pressure test but did not buy a micron gauge. I ran hour long vacuums though.

 

[kaffine]

The first one I did I just used gauges and a vacuum pump. I left the vacuum pump run for some time and it was a good quality pump. Run the vacuum pump and shut it off for a few minutes to check for any major leaks then started the pump and let it run for 30 minutes or so. That system has been running for over 15 years without having to do anything on the refrigerant side. I've had to tear into the blower motor to clean it a few times and reoil the bearings.

I now have more tools and last system required some brazing so I needed nitrogen purge for that, and got a micron gauge.

Do you have shielding gas for welding? Could use argon ect instead of nitrogen if you already have it.

 

[fitter30]

Since lines and equipment is new with a 500 lb nitrogen reg screwed all the way in pressure test the lines for 4-8 hours. Don't worry about pulling the schrader core blow the nitrogen evacuate for an hour put 50-100 lbs of nitrogen in it let sit for 30 minutes blow it evacuate for an hour open system valves remove gauges.
Reason i wouldn't come out to start up your system . Just because you say everything is ready ( since i don't know you) it might not be and don't want to straighten out any mistakes, bad workmanship or hidden problems.

 

[housewolf]

I was going to do mine myself, I worked in the business for my whole career, but couldn’t easily get my hands on a micron gauge when the time came. I called a local service company and they were happy to do it for $80.

In retrospect really all a micron gauge is going to do is give you assurance you’ve reached the point you want. It’s not going to magically give you a “deeper vacuum”. If you let the vacuum pump run a couple of hours and it holds a vacuum a couple of hours after the pump is shut off I really can’t see where you’d benefit from more other than knowing.

I’m sure someone will be along directly to point out the flaws in my logic.

 

[pcmeiners]

"In retrospect really all a micron gauge is going to do is give you assurance you’ve reached the point you want."

A micron gauge can let you know you have a slow leak, which a pressure test missed, slow or fast leak, you sill can burn out a compressor or at least need a service call for expensive gas. both of which could pay for a few micron gauges.

$80,.... good deal

 

[ps2cho]

I’ve spent many weeks on this question…I’m right at the stage now where you’re at. I ended up with #3 because I wanted to pressure test the lineset to ensure I had no leaks. Vacuum test has a risk of a phantom leak through the test setup versus a 350psi static test where you can bubble test all the fittings to know if it’s leaking at the line connection areas.. I’ve never flared anything and practicing on the leftover copper today to get it right with the Husky eccentric tool I got. But nonetheless since it’s my first time I can pressure test to be sure I don’t screw up.

I managed to find a used nitrogen bottle and regulator on Craigslist for $60 and went to welding supply store to trade out the empty bottle to a fresh nitrogen.

You can probably get away without the nitrogen if you ensure your flaring is good and you properly torque the flare nuts,. I wouldn’t do #1 though it’s too much of a gamble that your vacuum pump isn’t up to snuff. You just wouldn’t know.

Combo of Appion 5/16 and 1/4 valve core removal tool (Navac also has one I got it in 1/4 since Amazon delayed my Appion tool by weeks so swapped last minute and it arrived today, looks fine!) is the best way. $170 CPS micron gauge and $130 for the valve core removal tools and I have the assurances of being able to properly do this.

I’m pretty sure on eBay you could just resell these with minimal loss if $ is the concern. These are all high demand items.

 

[pcmeiners]

"Vacuum test won’t necessarily show a leak versus a 350psi static test."

As to a high pressure static test....

In most systems you do not have access to EVERY square inch of the system for testing, so a complete bubble test is impossible, unlikely a through electronic leak detection test can be done either (with certainty).

A high pressure static test will not show a very small gas leak using mechanical pressure gauges even over 24 hours of testing. The needle would not move in 24 hours with a small leak.

Micron gauges are extremely sensitive, generally micron gauges, on power up, start at 25000 microns. NO mechanical pressure gauge has 25000 increments. As to testing for leaks with a mechanical vacuum gauge, that is less accurate than with high static pressure gauge reading to find small leaks.

Basically the most efficient and accurate means of testing is to use both high pressure and a micron gauge to test for leaks under vacuum.

"You can probably get away without the nitrogen if you ensure your flaring is good"

You need nitrogen or another dry inert gas for the high pressure static test, as you can not use high pressure air due to moisture/oil/dirt .

Nitrogen purges speed up moisture removal, assures less residual moisture remains in the system after deep vacuum (even though it would not be critical amount).

Nitrogen molecules are 1000 times smaller than 410a or other refrigerants so if you have a small leak with static pressure, it will show up better with nitrogen.

 

[ps2cho]

I didn’t say he can pressurize with air - I just meant you can skip pressurizing at all if he had a micron gauge and is willing to accept the risks there. Doing neither a nitrogen pressure test nor having a micron gauge is rolling the dice. What if his vac pump only hits 1500 because it’s bad or oil issues? He wouldn’t know and it’s not deep enough even if he disconnected it and the mechanical gauge sat still.

Take all my posts with a grain of salt, this is my first time but I’ve spent considerable hours listening to pros (and there’s a ton of complete hacks out there…) so half the time is ignoring the scam artists who clearly skip purging lines or let the system return to atmosphere between evacuations defeating the whole point

 

[pcmeiners]

"I didn’t say he can pressurize with air"

Did not say you did. I mentioned it as added info for those that try short cuts.

I see you followed the best procedures.

 

[kaymccampbell]

I pretty much do #1, for flare connected, precharged mini-splits.
Vacuum for 30 minutes. Set for 30 minutes. Repeat 2 more times. I expect the needle to rise sometimes on the first vacuum. If there's nothing on the next 2, then I'm good. If not, then it's time to inspect connections. If all's well, then release the refrigerant, undo the coupling, to get a pressurized disconnect, light the unit, and we're off.

That said, all the other steps are a nicer process, but mine has never failed me. Big brazed units, get the full treatment, but nobody wants those anymore.

 

[racecougar]

I pretty much do #1, for flare connected, precharged mini-splits.
Vacuum for 30 minutes. Set for 30 minutes. Repeat 2 more times. I expect the needle to rise sometimes on the first vacuum. If there's nothing on the next 2, then I'm good. If not, then it's time to inspect connections. If all's well, then release the refrigerant, undo the coupling, to get a pressurized disconnect, light the unit, and we're off.

That said, all the other steps are a nicer process, but mine has never failed me. Big brazed units, get the full treatment, but nobody wants those anymore.

Ditto.

 

[maxki]

Ok,

I decided to go with option #3, got a micron gauge, the navac core tool changer, and a nitrogen regulator, and will be renting a nitrogen bottle.

Something tells me that all the costs and complications, is really like buying an insurance against mistakes that I could make with the flair connections.

It's probably not a "financialy sound" strategy, as I could probably have gotten a low risk, leaving the vacuum pump on for half a day, lengthen the vacuum decay test, etc, but I know I would have had regrets If the things fails in 2 years, and that regret is hard to quantify in monetary terms !

Also, I must admit I like tinkering this kinds of projects, so I can argue that it's "toy money" being spent ;-)

 

[pcmeiners]

"Something tells me that all the costs and complications, is really like buying an insurance against mistakes that I could make with the flair connections."

Rather cheap insurance as to buying the tools. Just one service call could easily cost more. At the moment I am installing 4 minisplits, that will be 6 total on my home and garage. so I purchased every tool I could need including gas recovery equipment..I will not need service calls