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Old 09-20-14, 08:55 PM   #11
F357
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One more question...

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Originally Posted by AC_Hacker View Post
In my experience, they're around halfish of what R22 was.
How do you know exactly when to stop pumping propane in?

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Old 09-20-14, 09:28 PM   #12
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Check the superheat to determine when there's the correct amount.
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Old 09-21-14, 03:26 AM   #13
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I think I might just end up using the compressor on this unit as a vacuum pump, and make a recovery machine for the next unit. Being at the end of summer they are just giving away air conditioners on craigslist! I've wanted to try propane for A/C for a while now, but I didn't realize the smell would be filtered out. That could be a problem. If I got set up to use and reuse R22, I have a lot of projects in mind.
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Old 09-21-14, 08:50 AM   #14
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Quote:
Originally Posted by F357 View Post
After doing a ton of googling I just want to make sure I have the basic procedure right...

1. Install service port like this on high and low side:
(Can't post ebay link, don't have enough posts here yet)

If you don't braze in fittings, flare them. Standard home a/c service fittings equal 1/4" flare. You can get flare nuts and fittings at home despot and slows; if you get bored and want to change something later, just crack theflares loose and rig something else in.

2. Hookup cheapest refrigeration gauge set I can find.

Make sure you can get replacement parts for your gauge set. If generic hoses won't fit or you can't get seals or valves,the set is basically disposable, a one-trick pony.

3. Pull vacuum on system.

A micron gauge will make this process much easier. Not using one is basically blindly trusting your vacuum pump.

4. Slowly fill with propane until the pressure is in the right range.

Does that sound about right? Are the high and low side pressures going to be about the same for propane? (Says 170/380 on the machine)
The pressures on the nameplate are maximum design pressures. Go above these and your plumbing could burst at any time.

Actual running pressures will vary upon conditions the unit is exposed to. On an 80 degree day, in cooling mode, mine runs around 65-80/170-180. Tune for superheat, not absolute chart pressure.
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Old 09-21-14, 09:23 AM   #15
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Is it OK to use compression fittings instead of brazing? The service valve I found on ebay is at the end of a short piece of 1/4" copper tubing.

To be honest it's all just an experiment at this point, this thing isn't really worth fixing with used A/C units going for $25-50 all over craigslist this time of year. I might just get a bigger one for my office...

Thanks for the information!
If you are shooting for cheap, brazing is the way to go. It takes a bit of practice, but brazed joints hold up where others fail. Ask me how I know.

On the same idea, just because you can find used window units cheap doesn't mean your modded machine is worth little. Used heat pump stuff and recovery devices are not cheap at all unless you are very lucky.

If you are considering building a recovery machine, use a compressor from a freezer that will pull a deep vacuum and not overheat. These also tend to not die if they ingest some liquid. The a/c pots aren't made to survive long when starved of gas to circulate. For your first project or two, just go to the zone and pony up the deposit for a loaner vacuum pump. After you learn how a real one acts, building one that works correctly will be easier.

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Old 09-21-14, 03:05 PM   #16
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Quote:
Originally Posted by F357 View Post
Is it OK to use compression fittings instead of brazing? The service valve I found on ebay is at the end of a short piece of 1/4" copper tubing.

To be honest it's all just an experiment at this point, this thing isn't really worth fixing with used A/C units going for $25-50 all over craigslist this time of year. I might just get a bigger one for my office...

Thanks for the information!
I can't tell if you are asking a question or if you are deciding to throw in the towel.

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Old 09-21-14, 11:39 PM   #17
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Quote:
Originally Posted by jeff5may View Post
If you are shooting for cheap, brazing is the way to go. It takes a bit of practice, but brazed joints hold up where others fail. Ask me how I know.
I read something about purging with nitrogen after brazing joints. Is this completely necessary?


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I can't tell if you are asking a question or if you are deciding to throw in the towel.

-AC
I'm going to find a bigger/better A/C unit while they are plentiful. Mine also needs a new fan motor. By the time I replace that, fix the leak, and recharge, I probably could have gotten a new one at Walmart...

I still want to hack it up and let the charge out, but hopefully I can reuse the R22 this time.

Back to my original question:
If I get another window unit, around 12k BTU, can I install some manual ball valves to reverse the cycle? That seems relatively easy, just flip the valves every season.
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Old 09-22-14, 12:13 AM   #18
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You use purge gas while brazing to avoid oxidizing the inside of the pipes. Copper likes to tarnish when it gets hot. If there's no oxygen, it can't tarnish and stays clean. The copper smut on the inside of the tube will flake off and clog up your system if you try to take a shortcut. I use propane as a purge gas, and it works well, as long as you discharge it away from where you are brazing. As always, proper active ventilation is essential when dealing with anything flammable.

As to your question about mechanical fittings, I like flare fittings second to brazed. They also take a little practice to do right the first time. The thing I like about flare fittings is they are not expensive, and they are readily available at hardware and plumbing stores.

I have seen compression fittings used in automotive applications, but they crimp the ferrule to the tube with a nut behind it, just like flare fittings. The fittings used are specialty fittings made just for auto a/c and are much more heavy duty than standard plumbing compression fittings. They aren't cheap, either.

Yes, you can manually reverse the flow with hand valves, but once you source the valves that will handle high pressure refrigerant and the tees and such to connect them all, you've spent more than the price of an ebay reversing valve. Also, in heating mode, the evaporator has a tendency to freeze up while noone is watching. A defrost control is a lifesaver during chilly weather.
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Old 09-22-14, 03:55 PM   #19
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Quote:
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Also, in heating mode, the evaporator has a tendency to freeze up while noone is watching. A defrost control is a lifesaver during chilly weather.
Would an oversized evaporator help with this?
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Old 09-22-14, 07:06 PM   #20
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Oversized heat exchangers help everything work more efficiently. The question is more dependent on your environment. If your outdoor temperatures stay above 40 degF, you shouldn't have problems with the unit freezing up. However, as outdoor temps approach freezing, it becomes impossible to extract heat without forming frost. Once the evaporator freezes up enough to impede airflow, the unit is done pumping heat until airflow is restored.

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