High pressure nitrogen test on new split A/C question

[scofo]

Long post!

I'm a retired CMAT and worked with auto A/C most of my career, to include, working at a shop from '86-'94 specializing in A/C & Electrical. I'm trying to finish up an install on a new R410a regular split system for my house. My question is to the HVAC Pros, mainly as their experiences would be great but any suggestions at this point would be appreciated.

Can nitrogen, unintentionally be, pushed through front seated service valves, into the precharged outside unit?

Install manual instructions have been followed except 3 deviations.

#1 I used Staybrite 8 w/stay clean flux.

#2 I wanted to take my leak check pressure to 380-400psi up from 150psi, system design pressure shows 448psi for both evap and OSU. The reason I wanted to do that was for our high ambient temps, the higher pressure of R410a and the OSU is pre charged so once I release the genie I'll need recovery assistance if leaks are found.

#3 I'm using Dawn liquid and water in a spray bottle to leak check with bubbles. Has work well in the past.

I ran low on nitrogen and could only develop about 200psi Friday evening,on initial leak check. The system held 200psi for an hour and no bubbles seen at joints. I then hooked up my vacuum pump with hose to an Appion valve core tool and a CPS digital micron guage. I pulled it down to 230mic and shut the valve off and disconnected vac pump. It rose to 240 at 20min, 280 at 40mins, 320 at 75mins, 360 at 130mins and finally to 380 at 140mins. This is well below the vacuum decay limit in the instructions.


Saturday I pick up a refilled Nitrogen tank and decide to attempt to achieve my higher pressure test. I run pressure up to 380psi and watched in disbelief as it drops to 360 in several minutes, I repeated this 3 more times as I go over the joints, drier,equalizer line, service and txv valves, manifold hoses, packing nuts, base of guages, no bubbles, nothing visual! It was continually dropping when I removed the guages and replaced the shrader caps leaving the 300+psi in it, a severe weather warning with chance of hail, I didnt want to leave my new guage set outside in the rain.

So last night I'm reading HVAC forums for things on pressure testing and found 2 references to the possibility of unintentionally pushing nitrogen past the service valves and I immediately get sick to my stomach. Could this be true? How could it hold charge in a hot warehouse or allow me to attain 230microns and hold 380mics? Did I somehow contaminate my yet to be released charge?

Today mid morning I quickly hook up the guages and find 235psi rising to 237 at heat of the day and staying there past 6pm. WTH is going on. I'm afraid to try another higher pressure test as I dont want to further contaminate but if it's already happened, well that's unfortunate.

Thanks in advance, Scot.


It's been a bit of a roller coaster trying to buy a digital manometer that was repeatable, a micron guage that doesn't leak and valves that dont seep in a deep vacuum. I currently have an Elitech and another CPS micron guages that leak internally but bleeding up vacuum to be useful for any thing. The defects will be sent back soon but it took 3 to get 1. Not good odds. No QC it would seem. So verify your micron guage before spending an hour pulling one down only to find your shiny new guage IS THE LEAK.

 

[Jim greengo]

I normally pressurize mine to the point where it hits the letter d in the word retard on the suction gauge,then I shut off the gauges and bottle.
I normally let it sit for about an hr before throwing the vacuum pump on it.
I've been a big fan of the stay brite8 since the early 90s,
I use it for all my plumbing and HVAC work,including 410a systems.

 

[justinjoyal]

Is it really a split or is it a mini-split ?

If it's a split with the metering device at the IDU, did you pressurize using both the low and high side ports to make sure the pressure is equalized ?

I would be surprised if it lost enough nitro to go from 380 psi to 235psi and then stopped leaking. Especially seeing how nice of a vacuum you had before.

If you pushed the nitro from one side only it could very well simply have equalized by its own and then just sat there.

 

[scofo]

Hi Jim, I reckon the d in retard is around 380-400, so that gives me some comfort on my overzealous pressure test and reassuring me on my use of SB8. Thanks.


Hi justinjoyal, It is a true split with txv at evap inlet on IDU. I only pressurized on the liquid line with only the high side half of manifold guage. I did spend over an hour leak checking and raised the pressure back to 380 at least three times during that time. I did this because I didnt want to expose my low side guage to the 380-400 I was attempting. However it looks like Jim G has no issue with taking the low side guage to the limit one more time ;-)
I hadnt considered that the pressure could/would NOT equalize across the txv over that amount of time. However that would be awesome if that is what occurred. Thanks

I just looked at my guages that I left in place overnight, 236psi still at 22hrs. I will raise my test pressure today on both sides evenly in 50+/- psi increments and see if there is a "break point" on its holding ability. If I get 380psi to hold and my evac is as good as the first one. I'll be ecstatic and my confidence will be high again. ***** when you lose your Mojo.

I didn't mention it but the evap did have that positive pressure that they ship with, in it still, when I opened it Friday, I've had it since last September. Of course used backup wrench for txv install and heat sinks when soldering the new line set. Hell, I even had a little nitrogen purge going during soldering, just because.

 

[fitter30]

Would not of used staybrite 8 for 410a 15% or dynaflow. When soldering lines to condenser did u wrap the valves with a wet rag? If the one of the valves is compromised the charge in condenser is no good. The evap coil just came with plastic caps or was it pressurized? With caps leak check it may cut the lines and pressurized it. Can't remember running across valve that didn't hold but found a few that the unit was empty.

 

[scofo]

Hey fitter30, yes wet rags were placed around the service valves and shraders removed during the soldering. As for as the evap, all the new ones seem have some pressure inside when manufactured. I dont know how much, I bled it off slowly, it wasn't refrigerant. Thanks for the reply.

I think justinjoyal nailed it. I will update everyone on this when I'm more certain.

I've had the line set and IDU at 380psi for over an hour and its holding. I let the nitro flow into both low and high side this time. I just thought the txv would have allowed equalization sooner when I doubted myself Saturday afternoon. As I had said I didnt want to expose my low guage to that pressure but they are designed for R410a so I was being over cautious, in that regard anyway. I'll let it set another hour and see where my pressure is. If 380 or higher I'll evacuate and hopefully release the genie later this afternoon.

I struggled with the braze v solder thing. Quite a bit of reading on HVAC forums it appears SB8 is used in R410a with success, with the exception of compressor outlet joints. While I didnt calculate all that I read it seemed like half soldered and half brazed, demographics seemed to be based on age, Older techs solder mostly and younger techs braze.

I did deviate from the manufacturer's install instructions statement to "braze joint using suitable brazing alloy for copper to copper joints".

I think it'll be okay but if the SB8 fails I'll know better next time.

 

[scofo]

Is it really a split or is it a mini-split ?

If it's a split with the metering device at the IDU, did you pressurize using both the low and high side ports to make sure the pressure is equalized ?

I would be surprised if it lost enough nitro to go from 380 psi to 235psi and then stopped leaking. Especially seeing how nice of a vacuum you had before.

If you pushed the nitro from one side only it could very well simply have equalized by its own and then just sat there.

Alright, I'm getting happier. I ran the pressure up to 380psi thru both sides this time. I closed the manifold valves and disconnected from nitrogen. >4hrs later it's a tiny bit >380psi, so a little expansion due to heat of day would be expected.

I'll move on to evacuation, as I'm convinced Justinjoyal's thoughts on slow equalization were spot on. Also to Jim G for talking me off the ledge on my "high" pressure test. More to follow if noteworthy.
Thanks again fellows

 

[Jim greengo]

Getting copper hot enough to braze affects the tensile strength of the copper,stay brite8 does not

 

[Aileron]

Getting copper hot enough to braze affects the tensile strength of the copper,stay brite8 does not

I've never had copper break because of a braze. 40 years as a UA pipefitter have never seen it happen. There is a reason every grocery store built uses silphous and high temp 45 or 56% connections. same with medical gas. i have seen it work harden but not break because of tensile strength. i have seen it over heated where it would not take silphous but still not break,.Its braze only on METU (mitshibishi /trane ) units, They did away with flare connections. Its also a 600 PSI pressure check.

 

[Jim greengo]

I've never had copper break because of a braze. 40 years as a UA pipefitter have never seen it happen. There is a reason every grocery store built uses silphous and high temp 45 or 56% connections. same with medical gas. i have seen it work harden but not break because of tensile strength. i have seen it over heated where it would not take silphous but still not break,.Its braze only on METU (mitshibishi /trane ) units, They did away with flare connections. Its also a 600 PSI pressure check.

Use what ever works best for you.

 

[American Locomotive]

FWIW: Depending on how quickly you charged the system with nitrogen, the gas filling up can actually get hot. When it cools, it will drop in pressure.

 

[scofo]

I dont think I dumped the nitrogen quickly but I suppose your hypothesis might be at least part of the pressure drop I experienced when I tried my first high(er) pressure leak test thru only the high side.

My evacuation, last Monday, was very good. Got to 190mic and isolated. Over two hours later it had only gone up to 270mic. So Monday evening I let the pre-charge enter the system and it went to work.

A/C is working great! What a relief, even with the window units I had going before, the living room would get up to 84* in the heat of the day and pretty much stay there until bedtime. The old mercury tsat is set at approx 78 and its 75* and 46% humidity in the living room mid 90's outside. The A/C runs about 30min per hour in the heat of the day. We'll see what it does in Aug. & Sept that is usually the toughest time of year.

The only complaint now is from my girlfriend about it being too cold for her. I need to fix my meter with the thermocouple or go a different route so I can check the subcooling and put a period on this little HVAC upgrade. Instructions claimed pre-charge was for a 15ft lineset. I used about 17ft from a 25ft set, so I'm sure I'm close and the TXV probably gives a little latitude.

When you pros and semi pros do an install and especially on your own home do you document the amp draws of the compressor and inducer, blower and condenser fans for future reference? Any opinions on anything else I should quantify/document after subcooling charge adjustment? I'm sure I'll be the guy repairing it going forward

I did document my propane pressure after adjusting it as I had to convert from NG. I also wrote down my dry static pressure, it was right on the money with my ductwork and the delivered IDU fan speed according to instruction manual.

That's where I'm at >6days in after starting up the A/C part of the install, the furnace worked great all 2-3 months of winter ;-) Thanks for the enlightenment and comments.

 

[LS6 Tommy]

Getting copper hot enough to braze affects the tensile strength of the copper,stay brite8 does not

Wives tale. Soft solder (including Staybrite #8) is NOT allowed by any manufacturer of 410A equipment. It will even void many warranties. Braze only...

 

[Jim greengo]

Wives tale. Soft solder (including Staybrite #8) is NOT allowed by any manufacturer of 410A equipment. It will even void many warranties. Braze only...

********,tell that to the supply houses that stock it on their shelves and send it out the door with 410a equipment every day of the week.

 

[pcmeiners]

"********,tell that to the supply houses that stock it on their shelves and send it out the door with 410a equipment every day of the week."

Find one r410a heat pump manufacturer who states soft solder is recommend or at least states it is OK for 410 lines. The issue with ANY solder is not that it does not initially work, the concern is over time the copper expands/contracts many times causing the solder to give way due to "solder fatigue". As to supply houses, they will sell anything to anyone if its legal.

Solder fatigue - Wikipedia

en.wikipedia.org

 

[Bruce_Sloane]

C'mon. Let the Gas loose
And Go

 

[bluedog225]

I dont think I dumped the nitrogen quickly but I suppose your hypothesis might be at least part of the pressure drop I experienced when I tried my first high(er) pressure leak test thru only the high side.

My evacuation, last Monday, was very good. Got to 190mic and isolated. Over two hours later it had only gone up to 270mic. So Monday evening I let the pre-charge enter the system and it went to work.

A/C is working great! What a relief, even with the window units I had going before, the living room would get up to 84* in the heat of the day and pretty much stay there until bedtime. The old mercury tsat is set at approx 78 and its 75* and 46% humidity in the living room mid 90's outside. The A/C runs about 30min per hour in the heat of the day. We'll see what it does in Aug. & Sept that is usually the toughest time of year.

The only complaint now is from my girlfriend about it being too cold for her. I need to fix my meter with the thermocouple or go a different route so I can check the subcooling and put a period on this little HVAC upgrade. Instructions claimed pre-charge was for a 15ft lineset. I used about 17ft from a 25ft set, so I'm sure I'm close and the TXV probably gives a little latitude.

When you pros and semi pros do an install and especially on your own home do you document the amp draws of the compressor and inducer, blower and condenser fans for future reference? Any opinions on anything else I should quantify/document after subcooling charge adjustment? I'm sure I'll be the guy repairing it going forward

I did document my propane pressure after adjusting it as I had to convert from NG. I also wrote down my dry static pressure, it was right on the money with my ductwork and the delivered IDU fan speed according to instruction manual.

That's where I'm at >6days in after starting up the A/C part of the install, the furnace worked great all 2-3 months of winter ;-) Thanks for the enlightenment and comments.

Curious what the tolerable increase in microns is? That is, how much is “ok.”

 

[pcmeiners]

Too many variables to answer how many microns, more like given enough time the micron changes slow down to a crawl, and vary up/down around an average point. It will never stop as temperature changes all the time

 

[Bruce_Sloane]

When it is at design Temperature in it should run continuous. Dont worry

 

[Bruce_Sloane]

Microns readings will rise when the pump is shut off. Perhaps 100, or so depending on the size of the system. You have done a fantastic job here don't over think it

 

[Dagny]

your fine.

 

[Jim greengo]

"********,tell that to the supply houses that stock it on their shelves and send it out the door with 410a equipment every day of the week."

Find one r410a heat pump manufacturer who states soft solder is recommend or at least states it is OK for 410 lines. The issue with ANY solder is not that it does not initially work, the concern is over time the copper expands/contracts many times causing the solder to give way due to "solder fatigue". As to supply houses, they will sell anything to anyone if its legal.

Solder fatigue - Wikipedia

en.wikipedia.org

You show me where it says in a manufacturer's warranty info where it says stay brite 8 cant be used with a 410a system.
There are plenty of 410a systems that are pushing the 20 years of service mark that I personally have installed with staybrite8 that have never had a problem with any solder joint failures.
So once again I call bull ****,jumping on the band wagon so you can sit with the popular kids in the lunch room means absolutely nothing if you've never actually used the product that your talking **** about.
I've seen plenty of lines broke at factory fittings coming off of compressors over the years,and here's a news flash: none
Of them left the factory soldered with staybrite 8.
The amount of heat required for your beloved hard solder cuts the tensile strength of copper in half,that leads to a lot of broken joints over time.
Use what ever makes you happy,and I'll use what works for me and everybody including my customers will be happy.

 

[Bruce_Sloane]

I quit Brazing 40 years agobever had a problem with StayBrite 8