[AC_Hacker]

Originally Posted by Piwoslaw

I have some questions:

While poking around at a scrap metal yard a few months ago and I saw a mini-split A/C unit waiting to be hauled off. It was the outdoor part (compressor, radiator, electronics, and all that) of a Sanyo SAP-CR224EHA and looked intact.

Here are some specs on the unit...

What you had there was a medium power unit, that could probably be made to work.

That unit was about the size of Xringers Sanyo.

Most likely, the controller was at fault.,

That unit was 3-phase, aprox. 400 volt.

Had a single speed compressor, so the controller would be pretty straight forward.

So why would a mini-split be at a junkyard? I mean, what could be broken and how hard would it be to fix it? What is usually the first thing to cause problems in mini-split units? When is it (Remember that I'll have to justify any expenses to the Wife.)

Most likely, the controller failed. It is possible to build another one. I find it much simpler to work with single phase.

And when is it feasible to grab one?

When you undertake something like this, you have to be calm, you have to be sober, and you have to meditate upon the idea that your wife might be much smarter than you are.

After you have done all that, then it is feasible.

The electronics? If so, is it possible to ditch the controller and force the unit to work, maybe swap a controller from another unit or make my own?

Yes to all of the above.

Understand what you are doing before you try to force a compressor to work. I do it all the time, but I am extremely attentive to detail and danger when I do it. I check the wiring several times before I turn on power, and I am ready to cut power in a split second if required.

In the USA the compressors have a "LRA rating" (Locked Rotor Amps). This means that if the compressor locks up, it will draw an amount of power equal to LRA (for instance 36 amps). So you will want to make sure that the breaker for the AC circuit is less than 36 amps, like 30 amps.

You really want some kind of time delay, as I mentioned elsewhere, to protect your compressor, when it is in normal use.

Currently, I am temperature regulating my GSHP with an AC line level thermostat. When the temp goes too high, a micro-switch cuts power, when the temp goes too low, power goes on. Very reliable, simple and cheap ($1, used).

I want to replace the line-level thermostat with a microprocessor that also has the delay, and other functions, but line AC thermostat is fine for now.

Or maybe there was a coolant leak? Are those hard to find and repair?

You need a complete circuit that you can pressurize with nitrogen or CO2 or some other inert gas, then get some soapy water and start looking for bubbles.

Once you find the leak, you'll need to braze it. so, you'll need a brazing setup.

You want inert gas inside the unit, but not under too much pressure, otherwise the inert gas escaping, will create an tiny pin-hole leak that is pretty hard to see, except with bubbles.

Compressor fault? Are compressors hard to fix, or maybe replace? Would it be possible to swap it for a compressor from a smaller model, and would that make it more efficient?

Compressors are very reliable. The cap usually goes first.

But if you tried to force the compressor to start, and you KNOW that you did it correctly and it didn't work, buy a new cap. If that hasn't fixed the problem, don't try to repair it. You might want to cut it open to see how it works but, other than that it only has scrap value.

Yes, you could go with a smaller one, I would try to stay close to the same size, not go under 50% of the original.

Also, can the indoor part of a mini-split be from a different model? Would taking it from a larger model increase efficiency?

Probably increase COP some. Try to stay close, as above

There is also the slim chance that the unit is OK and was thrown out only because it had been replaced with a different model.

Quite possibly so. The newer variable-speed units are more efficient (and tougher to hack).

BTW That scrap metal yard had some random A/C parts, too. Like Big radiators which would work great as heat exchangers in other projects.

... I think you are standing at the door to insanity, but we are here to pull you through!

If you buy something like that mini-split, you need to be of the mind that you may get nothing out of it but an education... That way, if you fail to get it working, it is not a total loss, and you may still be able to use some of the parts. You may want to keep this all in mind as you decide what you are willing to pay, too.

I don't know if you have any experience with HVAC or not. I would suggest starting with something much smaller and working up.

I would suggest a smaller single phase R-22 AC unit (R-290 compatible), you'll have plenty to learn about, believe me.

Remember to keep the metering device (cap tube or TXV) with the compressor, that will make the rest much easier.

You will also need to borrow or make or buy a really good vacuum pump and a refrigerant recovery unit.

You might be able to make these out of smaller AC compressors. Look around on the web, it's been done before.

Best Regards,

-AC_Hacker