Installing a ductless minisplit (the basics)

A licensed HVAC tech should be doing all of this and I am only posting these instructions for those that CAN'T have a tech around for security reasons.

Special tools you will need:

Vacuum pump (two stage preferred as it will get the vacuum lower, the larger the CFM the faster it will get the system pulled down)

Gauge set with hoses (don’t get cheap stuff here, bad idea)

Digital micron gauge (unless your manifold gauge set is digital)

R410a adapters - your fitting on the minisplit is a different size (5/16") than the gauge set and hoses (1/4").

Nitrogen tank and regulator (to pressure test the system)

Installation:

1. First you install the outdoor electrical disconnect, run the power as required for your unit. Make sure the disconnect is OFF until the unit is fully installed and ready to run.

2. Now you install the outdoor unit (condenser), make sure it’s level and not going to move in high winds. Connect power to the disconnect using the proper gauge whip.

3. Install the indoor unit/s. Make sure to run the condensate line to a drain.

4. Run the lineset/s. Don’t kink and avoid bends that are tight. You want the flare fittings to be perfectly aligned and tight but do not over tighten as this will damage the flare on the lineset.

5. Run the power between the outdoor unit and indoor unit/s (wire specs will be in the installation manual). There will usually be two cables, one for AC power and one for control signals.

6. Now you should connect the gauge set and pull a vacuum on the unit to get all the air out of the lineset and evaporator coil/s as it has moisture (bad), do this using the gauge set with the vacuum pump on the middle port. A good pump will take a few hours to pull it down enough for this step. Be sure to close the vacuum port on the gauge set BEFORE you turn off the pump or oil will be pulled into the system.

7. Now you pressure test using the nitrogen tank connected to the gauge set. You connect the nitrogen tank regulator to the middle port on the gauge set. The evaporator coil will determine the max pressure and you should test at that pressure with the nitrogen regulator setting (check installation manual). Go and listen for leaks at the fittings. Some people skip this step but if you have a leak at the fittings you will loose your refrigerant. Testing the system integrity with vacuum only is not recommended as a vacuum pulls fittings together where pressure pushes them apart plus you can't locate the leak by hearing the nitrogen escaping.

8. Once you are sure the system holds pressure you want to release the nitrogen from the system and pull a really hard vacuum. I let my pump run overnite if possible, make sure the pump doesn’t loose power of pump oil will be pulled into the lineset (bad news). You connect the pump to the middle port of the gauge. You want your final vacuum to be 500 microns or less before releasing the charge. Be sure to close the vacuum port on the gauge set BEFORE you turn off the pump or oil will be pulled into the system.

9. Once the vacuum is pulled you can release the charge that is held in the condenser unit. Make sure it's fully opened, it will stop. (usually done with an allen wrench on a valve that’s on the condenser unit fittings, consult your installation manual.)

10. Now you can run the system and make sure it’s cooling properly and there are no error codes. (This is when you turn on the power at the outdoor disconnect.)

TIP: Wear gloves when quickly disconnecting the gauge set from the charged system and a little refrigerant will come out and it's super cold, frostbite sucks.

These are VERY basic instructions. You can find videos online that show how do perform these steps in detail, closing and opening valves on the gauge set when needed is critical. Beginners should avoid pulling the schrader valve cores with a core removal tool, it speeds up the vacuum steps but if you damage the threads your gonna be hating life.

If you all see anything I missed let me know and I will edit the post.

Edit 1: Suggested by member Mont@n@ - You may need a flaring tool if you have bad flares or need to cut your line set. A flare torque wrench tool is recommended for the flare fittings.

It should be noted that some may think step 6 because pulling a vacuum before pressure testing with nitrogen is not needed. The reason you want to skip this step is simple. Pulling a vacuum before adding nitrogen ensures that no air (moisture) is in the system. When you pull a final vacuum any remaining nitrogen is much less of a hazard than air.

I apply a light coating of nylog on the flare fittings.

EDIT: lol

Renfro said:

It should be noted that some may think step 6 because pulling a vacuum before pressure testing with nitrogen is not needed. The reason you DON'T want to skip this step is simple. Pulling a vacuum before adding nitrogen ensures that no air (moisture) is in the system. When you pull a final vacuum any remaining nitrogen is much less of a hazard than air.

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I've read, outside the US, some units come pre charged, even the lines, they're sealed with shut off valves. Just hook everything up and open the valves and you're good. Supposedly the small amount of air in the connections is a non issue. Wish we could get them here so we didn't have to deal with charging.

WeedFreak78 said:

I've read, outside the US, some units come pre charged, even the lines, they're sealed with shut off valves. Just hook everything up and open the valves and you're good. Supposedly the small amount of air in the connections is a non issue. Wish we could get them here so we didn't have to deal with charging.

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Yeah not very many are like that. I personally don't like them because you are unable to do a nitrogen pressure test for leaks.

Sucks to put in a new AC unit, think all is well, get three or four weeks into a run and the AC is flashing a low refrigerant error code.

WeedFreak78 said:

I've read, outside the US, some units come pre charged, even the lines, they're sealed with shut off valves. Just hook everything up and open the valves and you're good. Supposedly the small amount of air in the connections is a non issue. Wish we could get them here so we didn't have to deal with charging.

Click to expand...

Even in the US, you can get pre-charged units. For a bit more money you can get the quick disconnect. This is the one I have. By myself, it took less than an hour and a half to more the unit for one room to another. With the pre charged, it has steps to purge the unit after the lines are connected. I am using an Ideal Air.

nevergoodenuf said:

Even in the US, you can get pre-charged units. For a bit more money you can get the quick disconnect. This is the one I have. By myself, it took less than an hour and a half to more the unit for one room to another. With the pre charged, it has steps to purge the unit after the lines are connected. I am using an Ideal Air.View attachment 4279311

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Unfortunately those are usually more expensive units. One of the things that we don't like about them is the line set isn't cut to fit and often there is a big loop of extra lineset left on one end. this is not workmanship like quality but as long as it's horizontal it won't effect operation.

WeedFreak78 said:

I've read, outside the US, some units come pre charged, even the lines, they're sealed with shut off valves. Just hook everything up and open the valves and you're good. Supposedly the small amount of air in the connections is a non issue. Wish we could get them here so we didn't have to deal with charging.

Click to expand...

MRCOOL Diy units are like this. I’ve installed 3 of them within the last 4 yrs and all are still going strong. You can order them through home depot. I got into doing regular setups myself now so i prob wont be going with the mrcools anymore. And I think the largest they got is a 3ton.

Renfro said:

Unfortunately those are usually more expensive units. One of the things that we don't like about them is the line set isn't cut to fit and often there is a big loop of extra lineset left on one end. this is not workmanship like quality but as long as it's horizontal it won't effect operation.

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Exactly. Those are hella bank when I was looking at them and like the MRCOOL DIY you will end up with that extra loop of lineset if the whole length of 25’ isn’t needed. But can be a very small price to pay if not comfortable with installing a regular unit without the quick connect precharged lineset i guess.