The Homemade Heat Pump Manifesto

[NiHaoMike]

Originally Posted by AC_Hacker

Here is one of the most informative sources of refrigeration hacking I have ever come across:

Phase Change Building Guide - XtremeSystems Forums

It has been considerably expanded since I first discovered it.

I'd advise you to read the whole thing, and when you are through, go back and read the whole thing again. This is an absolute gold mine.

Make note of the tools required, and start nailing down access to the stuff you're gonna need. You may have friends or relatives who have some of these tools to lend or give or sell cheap.

Sometimes Chinese tools can get you by:

Harbor Freight Tools

(* hint: don't even consider the 'Air Vacuum Pump', not good enough *)

Ebay is a good source of refrigeration servicing equipment. Here's a good starting point:

eBay ? HVAC Tools, HVAC Meter and HVAC Gauge items on eBay.com. Find IT on eBay.

Also, sadly, due to the horrible economic situation, there are HVAC techs who are forced to pawn their working tools. So check out the pawn shops, but don't go there until you have studied ebay, to familiarize yourself with what the going prices are. The pawn shop owners do this as a matter of course. Prepared yourself for some lively bargaining.

Do they have garage and estate sales where you live? Another good source.

And lastly, I'd advise you to read well the section on brazing. Then get some copper tubing and a MAPS tourch (Propane will work, only slower) and some silver brazing rod, some brazing flux, and start practicing. The infra-red energy of brazing isn't so good for your eyes, so don't neglect eye protection. An old welder told me that even plastic-lens sun glasses will offer protection, but you should double check that.

Regarding brazing, the tools and materials aren't so expensive and you can get some practice right away. I tried all kinds of brazing rod for this and didn't have any luck until I tried 40% silver rod. The silver content makes it flow really nicely. This stuff isn't cheap but you can get "job packs" with about 5 or 6 sticks.

The temperature at which the brazing rod flows well isn't very far away from the temperature at which copper slumps, so there is some skill there that you will have to develop. You'll want to have this skill on tap and well-developed before you hack into your AC unit. Resign yourself to the prospect that you may have a half dozen failures before you learn how to get one really pretty brazed joint.

You may even want to tackle a homemade brazed tub-in-tube heat exchanger.

Be patient, be persistent, you can do this.

Hope this helps...

I'll share my experience with refrigeration relating to a research project I did about refrigerating CPUs for higher performance.

Before doing anything else, research. It is very important if you want to assemble the device properly and have it work correctly on the first try. In particular, the TXV, as simple as it may seem, is one of the most difficult parts to understand. Make friends with a refrigeration engineer if you can. (In my case, the "fridge girl" I became friends with really helped me buy stuff, and not just by helping me select the right parts, as you'll see later.)

Then obtain the tools needed for refrigeration work. Some of the most common essentials are: a gauge set, vacuum pump, multimeter with thermal probe, MAPP or acetylene torch, and refrigerant can tap (if using refrigerant cans without nipples).

The gauge set is the most frequently used tool in refrigeration work. It mostly comes in 2 varieties - 2 valve and 4 valve. It is cheaper to convert a 2 valve gauge set into a 4 valve by adding a splitter and valves, although professionals may find that too clumsy. It's fine for DIY work, though. Expect to pay about $50 for a good entry level gauge set.

A vacuum pump is used to remove air and moisture from refrigeration plumbing. (Air and especially moisture can cause internal corrosion.) As previously mentioned, "jet" vacuum pumps are used for vacuum packing and are more or less worthless for refrigeration. I made my own vacuum pump from an old freezer compressor by replacing the oil with vacuum pump oil.

Unless you're going to use all flare connections (which have their own problems), you'll need a torch to "weld" (really more like high temperature soldering) the connections together. You'll need at least MAPP since propane does not get hot enough to make reliable connections. Acetylene is even hotter but much more expensive and overkill for our uses. You'll need welding rods made just for refrigeration since regular plumbing solder will crack and leak under pressure cycling. It will take a lot of practice to get it right. In my experience, the temperature is about right once the pipe starts glowing red.

Then you'll need parts and supplies. A cheap way to obtain many refrigeration parts is to buy an old refrigerator, freezer, A/C, or dehumidifier from Craigslist. (In my area, I have seen a listing for an old dehumidifier for $10. I'm going to make it into a small heat pump clothes dryer if it is still available.) You'll need to locate a refrigeration parts store in your area to buy service nipples, fittings, pipe, and some other parts and tools. Some stores are reluctant to sell to individuals (which makes no sense since they're losing a potential customer), so be prepared to locate another store to actually buy stuff. (I had a real problem buying a TXV for my CPU cooling project since only one store in my area had the right one available and they did not want to sell to me. The solution was to have my friend buy the part, which I then buy from her. Apparently, they could not resist selling supplies to a pretty customer!)

When it's time to start assembly, the parts to install last are the filter drier and (if prefilled with oil) the compressor. They will be degraded by exposure to air, so make all the other connections, then start pulling a vacuum after finishing the last connection ASAP. If you're reusing an old compressor, tape shut the pipes immediately after removing it and/or change the oil in it. If you're changing the oil, do not add the new oil until after the vacuum is pulled and then purged and leak tested with an inert gas. (Helium for inflating balloons works well, as does CO2 or nitrogen.)

If the first vacuum and leak check is fine, continue by releasing the pressure and pulling another vacuum for about 3-4 hours. Then purge with an inert gas to about 5 PSI of pressure and start another vacuum of about 3-4 hours. Repeat the purge and vacuum process again, then fill the system with refrigerant up to about 40PSI. Then start the system and continue filling until the sight glass fills up (if there is one) or until subcooling or superheat reaches the proper range.