To lower the vacuum is the lower the moisture left over in the system so lower is better although I'm quite sure that my sub 100 micron vacuums are overkill but why not. If I have other things to do finishing up it wouldn't make sense to stop what I am doing to charge the system up just because it hit 500 microns.
This was an LG refrigerator. [emoji16]

 

I’ve heard that below 100 microns you can do something bad to the oil but I’m not sure about all that.

On a coil and lineset then the lower the better imo. It’s really not difficult, especially on minisplits to get a new install (lineset and indoor coil) down to less than 100 if you use good evacuation practices.

 

It's BS. The oil is just fine.

 

yesterday I pulled 75 microns... but took long on a mini split. So wondering if it is worth it

 

On just the indoor and lineset or the outdoor unit was open as well?

 

Most new installs up to 5 tons (I've never done anything larger) take about 2 minutes to pass 500 microns.

 

Yea new installs usually don’t take more than 30 minutes including setup and break down to evacuate properly. I usually let it run longer while I’m finishing up other stuff anyway.

Outdoor unit Repairs is really where good evacuation process saves a lot of time.

 

I forgot this was in regards to mini splits... typically there is only 1 service port on the system.

Sent from my SM-S918U using Tapatalk

 

Me too. Now, I get it.

 

I remember the target value being 500 for years and years. I have seen specs for lower values same as you but I don't see where a variation in equipment application dictates a need for a specific target value, whether it's a mini-split or a freezer. A good pump on a clean, dry, oil free and tight (residential) system will usually pull down to or near, the capacity of the pump fairly quickly.

The critical aspect is whether or not it will hold 200 or 500 or whatever value.

But 500 was good 50 years ago, so it's good today for me...:grin2: ..and probably way better than what some of the other guys do when they hook up the pump, go to lunch, come back, open the service valves) and don't even own a vacuum gauge.

 

I agree with you but nobody, in residential hvac at least, was pulling a vacuum before 1993/94. It was all purge it and send it.

 

In the 70's I did commercial refrigeration & automotive A/C and we vacuumed the system. We used the compound gauge and when it hit 28" + 15 minutes, it was good to go. That was with R-12.

As I recall the only pumps I remember seeing was Robinair.

I remember using the "torch" type leak detector and when the flame turned a certain color you found the leak. Oh now I remember it was a Haylite torch or something like that. We were all excited when the TIF came out. But the torch worked better.

 

I remember 30 for 30

 

Double post. Sorry.

 

Micron gauges were just being introduced in the 70's. vac-n-all, mercury u-tube, or expensive absolute pressure gauges were the only accurate checks earlier.

Big pump without big hose does little.

Hold test more critical than pull down point.

 

re: Hold test more critical than pull down point.

+1 i quit bothering with micorn gauge many years ago as never do any work under about 30F. Water boils at 1000 microns at 2F, so that is plenty good to get rid of water in a half hour, esp if following short vac and N2 purge and 200-499 psi pressure test.

On minisplits, typically just pull vac with normal gauges till vac 'pegged', then let sit for 1/2 hour and verify no creep.

 

junkhound -
yikes! you are very confident of your setup! I always have problems with my setup but I persist until I get a good pulldown. I can see how your hold test may make up for not using a micron gauge but I'm still married to my gauge.

 

Purge with reefer and let it rip systems are still running 30yrs later and the garbage were installing we baby down to 100 microns and they still fail

 

Should always use best practice.

 

The decay test... There are no firm guidelines for the decay test? I know if the decay test goes above 2000 microns then you have a massive leak. I assume a pressurized leak test looks for leaks and a vacuum cycle is to remove undesirable contaminates. There is no such thing as perfection this side of the pearly gates so what gives?

There must be a million threads on decay test. I might have seen some posters say they pull down a system then do a decay test and finally it stops decaying. huh?

I have never seen that. I have never seen a micron reading level out at low levels (below 500). How long do you wait? I do pressure tests, waiting 24 hours and have some comfort with that but how long do you hold a vacuum.

 

A “perfect” evacuation should look like the graph posted in this thread somewhere back a page or 2 (or maybe another thread, but I’m sure you’ve seen the graph of BluVac pull-down) where it doesn’t sharply rise but slowly tapers off until it gets to the point of 1-5 microns per minute and stable over the course of a 30 minute blank off test. Nothing is completely impervious so there will always be decay.

 

500 microns is the most common mfg standard
.
Hold & rise is more critical where possibility of leaks or moisture is higher.
More volume, more time. Typically 1000 limit on rise, 1/2-1 hour on resi, 1-2 hour on rtu, 2-8 on large commercial & industrial.

 

So, are you saying if you pulled down to 500 and decayed to greater than 1500 in the respective time frames you cited, you would could consider that system as not being tight or completely dry?

I’m not challenging you, just looking for clarification and I’m curious about peoples perspectives as I hear so many different things. I’m generally good with physics but decay is just difficult for me to wrap my head around because it seems like there are too many intangible factors to quantify.

 

Wait !
Isn't vacuum pressure at atmosphere?
Who you going to scare with that?

 

If you are installing a new system it's documentation should state the parameters of the decay test and what the manufacturer considers to be an acceptable passing result.

 

May not be available from mfg.

 

I've seen on some older equipment they've recommended pulling vacuums under 800 microns, and I know with Goodman I've seen it say pull to 500 and hold for 10min with a rise to 1000, then I've noticed they changed it down to 250 and hold with a to no more than a 1000.

Personally I think anything under 400 microns is good, but I believe manufactures have been lowing the standards, because a lot of techs attach their micron gauges close to their vacuum pump and not getting a acurate reading. I usually pull from the suction line and attach my micron gauge to the liquid line, so when I valve off my pump for a 10min run time, I see it still dropping until it steadies out and holding under 250 microns within the 10min. This is my preferred method.

However, cause mini splits don't have a liquid line dryer installed, I also follow their triple vac method, which works well to.

Just sharing my thoughts.

 

I connect the pump to the vapor line and the micron gauge to the liquid line, each with an Appion core tool. Assuming the system is 100% sealed, it should not matter where you put the micron gauge, but this method ensures you're pulling and measuring vacuum across the entire system.

 

Isn't there a liquid line filter dryer inside the outdoor unit?

 

Not on a mini split.

 

Those minis are pretty tight quarters.

 

Nope

 

There not installed from the factory so why change the design?

 

Specifically regarding mini splits, your install practices are supposed to be worthy enough that no filter drier is required.

If you had a burnout and required system clean up, I would think a suction filter at the outdoor unit would be installed. But I don't think I have ever seen that.

 

This was a nice evacuation.

It was a 3 ton Spacepak air handler with a 3 ton Bosch 15 seer heat pump. New line set (about 20 feet).

That little hiccup in the graph around 5000 µm was me actuating the CRT ball valves to clear them out.

That little step down near the end of the evacuation is where lost connectivity to between the vacuum gauge and the phone for a short time because I had to wander away.

The decay test was beautiful. It rose up a little bit and then flattened off to a 0 µm per minute change.

After it passes the decay test I always give one more pull with the vacuum pump before I release the charge.

 

The deeper the vacuum, the dryer the system will be before charging. The dryer the system is before introducing refrigerant, the better. I will not install any system without doing a triple evacuation to get the lineset and coils as dry as humanly possible. It's extra important to evacuate moisture and other condensibles in minisplits, where the tubing is smaller than in a normal split system. A good two-stage vacuum pump with fresh oil should be able to pull down to low triple-digit or even double-digit microns on a tight system by round 3 of a triple evac. It's worth the effort. If the system pulls down to low digit microns and holds there for 20-30 minutes, you have a tight and dry system and you're good to go. Otherwise, break vacuum with nitrogen and pull it back down. You'll break vacuum on the last round of evacuation by releasing the refrigerant charge, not with nitrogen.