Evacuating mini split in cold weather.

Brian26

I plan on installing my mini split tomorrow and the weather will be in the 30's. I will be using a core removal tool, micron gauge, and vacuum rated hose. Is it ok to evacuate in cold weather or should I wait for it to warm up? I assume the little moisture would still boil off even if its cold around freezing out?

The condenser is precharged and the evaporator is filled with nitrogen. Line set is about 12 feet so I would just be evacuating the lineset and evaporator.

ratio

Flush with nitrogen prior to starting & a triple evac, & you should be fine.

EBEBRATT-Ed

You will probably be fine doing what @ratio said but....I wouldn't do it unless for some reason it had to run and you have no choice.

Look up the temperature at which water will boil and the vacuum required to make it boil.

When you get below 50 deg evacuation will be very slow. You could warm things up with heat lamps/guns carefully

NY_Rob

With just one 12' lineset for vacuum, don't be surprised/disappointed if you see big swings on the micron gauge when working with the core remover tool (when storing the core/reinserting it and working the tool's valve). Any air ingress in such a small container will show up big on the micron gauge.

GW

New system? No sweat. It’s more of a pain to pull on the condenser/compressor but you’re just talking new piping and new indoor unit? Cake.

Are you a triple guy? Years ago I was bamboozled and stumped. Now it’s so silly easy, second nature

When it gets in the 20s and colder it’s good to warm up the Sevice valve a bit before you open it (per Mitsubishi tech). I carry a heat gun for this

GW

> @NY_Rob said:
> With just one 12' lineset for vacuum, don't be surprised/disappointed if you see big swings on the micron gauge when working with the core remover tool (when storing the core/reinserting it and working the tool's valve). Any air ingress in such a small container will show up big on the micron gauge.


Rob I don’t follow, can you reword a little? I haven’t seen swings unless there’s a leak

ratio

With the N₂ flush & triple evac there really shouldn't be too much H₂O left in the system. But pulling down a system in the winter sucks. Let the pump warm up.

Harvey Ramer

I find that new installs in the winter pull down quick and easy. If you think about it, the ambient temp is lower and the relative humidity is much lower as well. Therefore, the absolute humidity inside any piping that gets exposure to the atmosphere will be very low. Less moisture, faster evac.

The biggest enemy is leaking hose fittings. The cold will shrink and harden the rubber seals. It's a good idea to keep the tools warm till you are ready to use them.

GW

If I was pulling on the condenser in mid winter it’s best to get a small 5000 watt heater sitting in there to warm up the oil a bit. If you want to be extra on the ball get a tarp or whatever to cover the entire outdoor unit. But a new piping new indoor pull is pretty normal. Good point Harvey may need to Nylog the the hose connections for added specialness

NY_Rob

GW said:

> @NY_Rob said:

> With just one 12' lineset for vacuum, don't be surprised/disappointed if you see big swings on the micron gauge when working with the core remover tool (when storing the core/reinserting it and working the tool's valve). Any air ingress in such a small container will show up big on the micron gauge.





Rob I don’t follow, can you reword a little? I haven’t seen swings unless there’s a leak

Same principle as removing a cup of water from a pint container vs removing a cup of water from a bathtub. In one case a cup is half it's volume and you'll easily notice it- in the other case it's a fraction of a percent and you probably couldn't even measure it.

Last spring when evacuating my full system with three indoor units and 135' of lineset.. when working with the core remover tool (in/out/replace, etc..) the micron gauge held steady when operating the core tool. When I worked on my other system and just evacuated one indoor unit with a 20' lineset by itself (when I was down at 200 microns or so) just working with the core remover would result in the micron gauge showing a decent loss (10-15microns) of vacuum.

In both cases I used the same core remover/micron gauge/pump/etc... just different system volumes between a three indoor units/135' lineset setup and just one 7KBTU indoor unit and a 20' lineset setup.

Funny thing is, I thought evacuating the single head job was going to be a quick in/out/done thing. But due to the small system volume it was more difficult... you had to be super careful with all valves and tools to prevent any leaks at 200 microns and below.

GW

Ok I guess I still don’t follow. You know that when you turn off the core tool you get an automatic spike (drop in vac) due to oily matter building in the tool itself ? But never the less, yes it will spike then drop quickly to about where it was “running”

Dave0176

I always use Nylog on the hose connection, it almost seems if I skip that step I never pull the vacuum as deep as with.

Harvey Ramer

Core removal tools have ball valves. There is a hollow cavity between the outside of the ball and the sidewalls of the tool. When you turn the valve, this hollow cavity gets exposed to the system until the valve is fully closed.

You have to depressurize the core removal tool during every evacuation. I usually wait till I'm around 500 or lower microns and the crack the valves until my micron readings drop back as they were.

NY_Rob

^ thanks Harvey, that probably explains the "blip" I'm seeing on the micron gauge when operating the core tool. Also, once you're done with evac and ready to replace the core... you get a small pocket of air in the core chamber too when switching from vac hose to core stem tool.


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GW

Rob you gotta open the charge on the condenser to break the vacuum, Then put your Schaeder core back in

I like the copper line for the vac

apraetor

All liquid water will boil in a vacuum, even below freezing. It would take longer to sublimate water ice, but at or above freezing it'll all boil off in short order. The exception will be a mono-molecular layer of water which will remain through adsorption.

To remove that (we do this is for medical equipment) requires heating the copper to 100 C while pulling 10-^9 torr (about 10^-7 micron if I converted correctly). Needless to say, we use ultra-pure nitrogen during a let-up and try very very hard to keep air from getting in.

GW

And don’t forget to torque down the non used zone flare caps 😄

Leonard

Not much experience in the cold, but I'ld warm valves before turning them, same with inserting/removing shrader valve. Plastic seals gets stiff in cold and might not seal. I've seen 2# propane can fittings leak in the cold after torch is removed and I 've broken lot of plastic stuff in cars when cold.

Look at pressure/temp curve/tables for water boiling. Think you want ambient temp to be a good amount over boiling temp of water, so tubing can rewarm after some water boils off. This means need a harder vacuum in colder temps. . But your hose seal might be cold and not seal as well in the cold ( heat them and fittings first)

Don't know if actually will boil off enough water to cool tubing much, suspect it won't too much. But I have not run the numbers. So not knowing any better I'ld GUESSTIMATE add at least a 10-20 degree margin. Just theory not experience. I changed my car evaporator in summer.

NY_Rob

GW said:

Rob you gotta open the charge on the condenser to break the vacuum, Then put your Schaeder core back in



I like the copper line for the vac

Thanks for that!

In my configuration, would that positive pressure inrush damage my micron gauge?

GW

I think the vacuum gauge is designed to handle at least 100 psi probably more. But worse yet you really don’t want Oil’s getting in there. The next time we do it Ductless I’ll take a picture of our set up.

NY_Rob

Would appreciate that Gary, thanks!

Here are some snapshots I gathered from around the web regarding placement of the core remover tool. Both setups would subject the micron gauges to pressure and refrigerant if the service valve was cracked with the core tool in place.

GW

I found a pic, so you can’t see it super well but we do have a ball valve on the vac gauge. And you can see our triple set up. In case anyone wants to hear—-When we “gas it” (our expression for the “triple evac”), we shut off the top valve on the manifold tree and also the valve on the vac and we gas it to 10 psi or so. Then we slowly open the top valve on the tree (yes it sputters some) until we get below zero psi (that’s takes a second or two) then we open the valve again for the vac gauge.

NY_Rob

Thanks Gary, that makes sense now.

After final purge/evac... Close the ball valve to the micron gauge then crack the service valve, install core under positive pressure, then remove the core tool from the service port.

That works for me and no chance of damaging or contaminating the $$ micron gauge.

PS.. like your homemade “gas it” setup... looks like it's better suited for purge/evac than using a manifold set.

LOL... on my first purge/evac to 500 microns I didn't realize I'd lose the vac as soon as I turned the pump off. Fixed that real quick..

GW

Cool. Running a vac though a regular gauge set seems silly but that's just me. The hoses should be well suited for the vac process

GW

Here's another variation. Basically the fewer valves you have the less chance of leaking (getting a good vac)

NY_Rob

If I was a professional I'd make up a simple/efficient rig like that!

Of course, you have to start off with a decent pump and fresh oil too.