Question on reusing a mini split.

[jezze269]

A few weeks ago I bought a Friedrich 22000 but mini split used off of craigslist. I did not do enough research before I bought it. I saw the $200 price and thought it was a good deal. The unit was manufactured in 2016 and the previous owner removed it after a remodel.

https://www.supplyhouse.com/Friedrich-MM24YJ-22000-BTU-Floating-Air-Wall-Mounted-Ductless-AC-Heat-Pump-Package#qna-content-container

The main concern is after I got it home I found the service valves were open leaving the system open to ambient air. I started reading the POE oil is extremely hydroscopic and sound like they only way to replace the oil is to cut the compressor out and drain it out. That is a little more than I would like to deal with. I thought about risking it and just installing it, purging it with nitrogen buy a micron gauge and run a proper vacuum on it.

I would have the $200 initial investment, 3.5 lb of 410a, lineset, forged line nuts, micron gauge, flaring tool, vacuum pump, manifold gauges, and a scale. The pump, scale and manifold gauges could be used with auto hvac projects I have but its still not too far off of a new, decent name brand unit that is precharged, includes includes lineset. I would still need gauges, micron gauge, nitrogen, and vacuum pump.

Any thoughts or advice would be appreciated.

 

[Noltz]

I am an automotive mechanic and routinely run into vehicles that have been crashed and their AC systems left open for weeks. When I do the repairs I'll leave the systems under a vacuum for a half hour or longer to try to draw out as much moisture as I can, but I don't go pulling compressors to drain the oil. I'll add the appropriate oil for the new parts (usually a condenser and lines, 4-6oz typically) and run the system. I do a performance check at the vents and send it.

In this case I'd do the same, but orientate the condenser unit so the service ports are at the lowest point and let any standing oil drain out. Install your system and pull a deep vacuum. Get it down to -30" and leave it overnight. Run it for another 15 minutes in the AM just to evacuate any moisture that managed to boil but wasn't enough to move the needle. If 410 doesn't have oil then add your own and charge the system.

 

[b-nasty]

In theory, you should have the micron gauge and a decent vac for any install new or used. So, assuming you buy those, I'd probably hook the indoor and outdoor units together with a short bit of scrap pipe and do a standard vac down and decay test. If you can get it to sub 300 microns (run the pump for at least 2 hours) and it holds that for a few hours, I think you're good. They say you can't pull the moisture out even with a sub-500m vac, but I doubt it matters much.

Honestly, I'd be more concerned that the flare faces on the units are scratched, or the threads are deformed from the original flare connections. The small amount of moisture absorbed by the oil, though not ideal, isn't likely to meaningfully shorten the unit's life. However, if you can't get good flare seals because the P.O. torqued by feel or damaged the brass connectors, a gas leak is going to be much more of an immediate problem.

 

[jjrbus]

I have done 3 DIY mini' installs and now working on a leaking coil and a fault code. Mini is more computer than HVAC. Knowing that the unit was not removed properly pumped down and
sealed, I would assume it was not installed right. Once it is installed and there is an issue a DIY guy like me is in over my head trying to diagnose. I have the service manual for mine, it is written in Chinese algebra. I would eat the $200 or try and sell it, they are worth a few bucks in parts. Could be a piece of cake or a nightmare. If you decide to do it, look up triple evacuation.

My opinion and worth what you are paying for it!

 

[justinjoyal]

For that price, dont sweat it…

Purge the whole system with nitro, pull a good vacuum (sub 500 microns) and let it rip. It’ll be fine…

 

[jezze269]

Thanks for the advice everyone. Any suggestions on budget friendly vacuum pump that is adequate to get the job done?

 

[bonneyman]

One thing I know about R410a synthetic oil is that you can't remove all moisture from such a system with a vacuum pump only. The moisture chemically combines with the oil, making a filter/dryer necessary to remove it. (Plus the chemical by-products could contain acid). As has been said above, for the price you paid I'd try and use it.
I'd try and flush all the stuff out in the lines and coil, take your chances on the oil in the compressor crankcase is relatively unscathed. But beware it might not last long. JMHO

410a moisture issues.

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[jjrbus]

Thanks for the advice everyone. Any suggestions on budget friendly vacuum pump that is adequate to get the job done?

I use a pump from Harbor freight. You could also rent one from Auto Zone for free. I would change the oil in AZ pump as they do not change it but only add oil. https://www.napaonline.com/en/p/NTE783910?cid=paidsearch_shopping_dcoe_google&campaign=GSC-https://www.napaonline.com/en/p/NTE...VRkzDyz8DT_U6XYSv0aAmFnEALw_wcB&gclsrc=aw.ds&

 

[jkuro]

As said above, run the vacuum pump all day and night. Free to rent pump and gauges at most auto parts. Replace filter dryer or add one if it's gone.

 

[jezze269]

I’ve been reading mini splits don’t/can’t use filter driers. Not sure why though

 

[b-nasty]

As said above, run the vacuum pump all day and night. Free to rent pump and gauges at most auto parts. Replace filter dryer or add one if it's gone.

If you have the micron gauge and Appion core tool, you can do quick tests of decay to see when you're getting close. Run the pump until it drops to around 200-250m, close the valve and see how fast it rises. If it holds steady, you're done.

The recent install I did, with 45' of lineset (that I wasn't super great about keeping capped) required about an hour to get to 200m. It held rock steady at 200-220m for an hour after that. No need to run the pump any longer

 

[fitter30]

I’ve been reading mini splits don’t/can’t use filter driers. Not sure why though

The metering device txv is located in the condenser thats why both lines are insulated and cold in cooling and hot in heat.

 

[fitter30]

Most minis don't have driers just a strainer and its buried in the condenser before the metering device. Line set lines are Not a liquid line. Dries are installed the the liquid line and for a contaminated system ( compressor burnout) a suction drier. Minis use poe oil once contaminated by moisture a vacuum will not remove it the only way is drain and refill. Minis don't have a way to easily drain and refill the oil.

 

[metlmunchr]

I've never looked at the internal piping layout of a mini outdoor unit, but I'd assume in heating mode it would function much the same as any other heat pump where the indoor coil effectively becomes the condenser and heat is extracted from a high pressure gas and converted to a high pressure liquid.

Assuming that's the case, is there some reason why the OP couldn't install a liquid line drier in the return line to the ODU and run the unit in heat mode to remove the moisture? Obviously you'd use a bi-directional drier in case the unit goes into defrost and ultimately pump the unit down and remove the drier, but it seems like that would work unless I'm missing something.

 

[LS6 Tommy]

For that price, dont sweat it…

Purge the whole system with nitro, pull a good vacuum (sub 500 microns) and let it rip. It’ll be fine…

X2 for $200...