[Rane69]

ok. curious what you guys think
typically if i install a new unit and the condenser has a pre- charge (mainly ductless units but guess it could apply to any pre- charged unit) i am a true believer not to pressure test with nitrogen as to not contaminate with non condensables due to valves leaking by or venturi effect.
in the process now of evacuating several ductless units and using vacuum pump for leak checking
the way i see it. if after ive reached 500 or less on micron gauge i shut and valve pump off
if my gauge goes above 1000 after sitting for half hr then i have moisture still in system. if it goes above 5000 then its a leak. usually it withh rise 200 or so microns and stay there
is this as reliable as puting unit under 200 lb nitrogen pressure

 

[gravity]

Sometimes you may find a leak in a vacuum and not under pressure and vice versa. It is rare but, it does happen. I understand your methods and seems like it would work.

If you leak it shouldnt be much trouble. There is no oil in the lines to saturate with moisture.

I would take a temp reading of where the unit sits. For example...its 90* at the pre-charged unit and it is using 410a. The pressure in the unit should be 275psi. I would pressure test at 250. This way you assure the nitrogen cant mix with the refrigerant if the valves dont hold.

 

[BBeerme]

If you are concerned about the valves holding the charge in properly in a pre-charged unit (or nitrogen getting in the pre-charged system), then just use your leak checker before you begin brazing up the lines. Check the valves to be sure they are holding.

Although I've never done that, it would be a real pisser to think you had a leak in your piping when all the while it was a leaky isolation valve.

 

[Rane69]

basically is this an acceptable way to leak check. i always use nitrogen on dry systems
it seems most instructions that come with ductless units do not mention nitrogen and recommend vacuum method
guess we will find out when we start the 5o plus units
hope this doesnt turn into a nightmare

 

[BBeerme]

basically is this an acceptable way to leak check. i always use nitrogen on dry systems

On another thread dealing specifically with using a micron meter for leak checking, I said the only time it seemed valid to me was on a brand new system, similar to what you have here. And it seems I took some heat for that stance.

But for me doing emergency service, I would spend untold hours in a day waiting for the vacuum pump to pull down. You essentially get all of the air out pretty quick. Then you are just boiling the refrigerant out of the oil. And that can take a long time.

Which is why I say that I only use a micron gauge on brand new piping. And you will get fast results. But far and above all else, for leak checking, the H-10 is the gold standard.

 

[jtrammel]

I always pressure test to ~150psig for 10-20 minutes then pull a vac to at least 500 microns and hold below 1000 for 10 minutes. If you vacuum and have a leak then you are pulling in moisture.

 

[Rane69]

I always pressure test to ~150psig for 10-20 minutes then pull a vac to at least 500 microns and hold below 1000 for 10 minutes. If you vacuum and have a leak then you are pulling in moisture.

if i had a leak i would fix it thhen evacuate until i reach appropriate micron levels
the units im dealing with, like most ductless splits pull down quick
my concern is why the manufacturer recommends this method to leak check and evacuate
again this is not a typical way i would leak check and evacuate
i think best is to pipe in air handler, do not connect condenser and pressure test lineset and air handler with nitro
then make your flares at condenser and evacuate

 

[Rane69]

forgive me but what is "h-10"

 

[BBeerme]

forgive me but what is "h-10"

It is a leak detector that has been around for decades and is about the best you can get.

http://www.bacharach-inc.com/h-10g.htm

Every other leak detector is measured against this one to see how good it is. It will detect something like 1/2 of one ounce per year leak. That's pretty small, or good, depending on how you are looking at things.

It is perhaps the single first "major" investment for the beginning tech. There is a battery operated version that I have heard works just as well, but I haven't upgraded to that. My first one was a H-10A, now I'm up to a H-10G.

 

[Rane69]

i have a d-tek. hasnt let me down yet

 

[burner guy]

I don't see how pulling a vacuum could EVER be regarded as an acceptable means of ensuring a system is leak free. Look at the logic... Atmospheric pressure at sea level is 14.7 PSI. If it were physically possible to pull a perfect vacuum, you would only creating a pressure difference of 14.7 PSI. I interpret this as the same as pressure testing at 14.7 PSI.

Also, all of the components of an A/C or refrigeration system are designed to hold pressure in, not to hold against external pressure.

Always do a nitrogen pressure test.

 

[toptech]

if your cups are filled and ya pull a 300 micron vac your good to go.
That said, r410A is pretty wicked when the pipes come apart at 400 psig.
we all purge nitro when brazing so spend the extra 15 min to half hour and be safe.

 

[Rane69]

well out of 50 units ive found three with very tiny leaks micron gauge not able to pull down and hold
pressure tested with 150 # nitro and had a hard time finding leak
let nitro go and introduced some 410a then sniffed out and found on flare
im not saying this is my preferred method of leak checking but after doing so many units i have to say it works

i think i would only do this on small new systems
on a large system it would take too long and not be worth it

 

[toptech]

well out of 50 units ive found three with very tiny leaks micron gauge not able to pull down and hold
pressure tested with 150 # nitro and had a hard time finding leak
let nitro go and introduced some 410a then sniffed out and found on flare
im not saying this is my preferred method of leak checking but after doing so many units i have to say it works

i think i would only do this on small new systems
on a large system it would take too long and not be worth it

the pressure test imho is protection from joint failure when your not onsite. Its a controlled disaster test and ensures you bonded the pipe properly at your highest operating pressures. Added bonus is you'll here any pinhole leaks in your joints.
Micron gauge is insurance your refrigerant charge will be intact in the spring. Small or large systems is not a factor if your removing cores in your access fittings while evacuating. Just did a 70 ton circuit at 270 microns in about 20 min with a single 7 cfm pump.

 

[bullcity]

I worked with a Sr. tech the other day on an install job replacing an old air handler. He chose to leak check using a vacuum instead of nitrogen. The following day I was called back to to the business on a no cooling call for the same system. The unit completely lost it's charge. Needless to say I felt responsible but I didn't want to step on his toes by second guessing his decision. As, I am fairly new to the trade I think I will take my chances and continue to pressure test with nitrogen.

 

[Mike19]

If anyone really wants to get particular with a new install, I've got a handbook that says:

Pressure test system with a trace charge of R22, then increase test pressure to 150psi with nitrogen.

Leak check the entire system using an electronic leak detector.

If no leaks are found release the nitrogen/refrigerant mix and evacuate the system below 1000 microns.

Break the vacuum with dry nitrogen, and evacuate the system to 500 microns.

Break the vacuum with dry nitrogen, and evacuate the system below 300 microns. At progressive intervals, isolate the vacuum pump from the system. Once the micron reading holds steady below 300 microns while isolated, the evacuation can be considered complete. Leave the system isolated and if the vacuum is held below 300 microns for 24 hours the system can be considered leak free.

This test will only be possible on installs of new piping systems. The outgassing of refrigerant from oil will not allow for a steady micron reading on systems that have already been in use. The compressors should also be isolated to prevent outgassing of the oil.

 

[BBeerme]

If anyone really wants to get particular with a new install, I've got a handbook that says:

Pressure test system with a trace charge of R22, then increase test pressure to 150psi with nitrogen.

Leak check the entire system using an electronic leak detector.

If no leaks are found release the nitrogen/refrigerant mix and evacuate the system below 1000 microns.

Break the vacuum with dry nitrogen, and evacuate the system to 500 microns.

Break the vacuum with dry nitrogen, and evacuate the system below 300 microns. At progressive intervals, isolate the vacuum pump from the system. Once the micron reading holds steady below 300 microns while isolated, the evacuation can be considered complete. Leave the system isolated and if the vacuum is held below 300 microns for 24 hours the system can be considered leak free.

This test will only be possible on installs of new piping systems. The outgassing of refrigerant from oil will not allow for a steady micron reading on systems that have already been in use. The compressors should also be isolated to prevent outgassing of the oil.

Ahh, the updated version of the classic triple evacuation. When I first learned about the triple evac we would break the vacuum with the refrigerant. It was so much easier back then . . .

 

[ICanHas]

I've read that vacuum is a better method for sensitivity, but you better make sure what fittings you use to blank off, because valve stems on ball valves and manifold valves are notorious for inward leaks which cause a false leak alarm.

As a general practice, I like to quickly go over with a leak detector if the system isn't flat. If the system is flat, I would add 30-50 psi nitrogen FIRST, then look for gross leaks. The ones that make the gauge go down noticeably within 10-15 minutes or the ones you can hear. I don't recommend pulling a vacuum until you pass this for the sake of not admitting air or water from wet coil into the system.

Manifolds generally use valves similar to the type used in a traditional faucet. They're not back seating, so the stem seal is created by o-ring(s). Each spool uses anywhere from one to three o-rings. When its pressurized, the pressure tends to expand the o-rings out and help make the seal tighter. It's possible to have no detectable leak under pressure, but leak under vacuum. Vacuum does not provide the favorable sealing forces. It actually has negative forces that tend to unseat the o-ring.

 

[Capz]

Water boils at 69F at 18,288 microns, and at 2000 microns water will boil off at 15F. You want guess at what temp water will boil at 500mi?

Not saying I don't pressure test with 100 psi n2 before evacuating but I don't become concerned with any air which slips past my hose or a leak so small I can't find it with soap. I know I'll boil off amy moisture in the first hr or so.