DIY reclaiming of freon -- thoughts on servicing A/C

[FastWoman]

Hi all,

Sorry to be such a stranger. Life gets in the way, I guess. Mostly I'm away from my computer, which makes me more productive, but less communicative.

Anyway, I've been dealing with the 134a A/C on my Saturn (yes, I know, not a Z) and have some further ideas that might help people with their systems.

First, I have to compare the performance of my '78 Z with exactly 2 pounds of R12 (per specifications), vs. my Saturn with an unknown quantity of R134a, which I just topped off. The Z blows ice cold , while the Saturn is pleasantly cool. I think the difference is that the charge on the Z is exact, while the charge on the Saturn is approximate. Although I can get a vague notion of freon levels from operating pressures, etc., I have to say that topping off a system seems to be more of an art than a science. From what I can glean from the Intenet and from various service manuals, nobody seems to commit to hard numbers and objective criteria for determining what is a full charge. The best criterion for a full charge on my saturn is the specified 1.5 lb of R134a that it takes, when charging from an evacuated state.

So I'm left thinking the best way to service our A/C systems is not to top off, but rather to evacuate and then recharge. So how might one do this without fancy equipment, without venting (much) precious R12 to the atmosphere, and without violating the law? Here's how:

First, you need an old freon can with the tap. If your system isn't cooling much, chances are that you have much less than one pound in your system -- enough to recapture into a 1 pound can.

First evacuate your can with a vacuum pump. If this is not possible, then alternately let the can pressurize with freon from the L side, close off the L side, then vent the can out. Do this 3 times, and almost no atmospheric gasses will be present in the can (roughly 1/125 of what was there originally). Yes, this is venting freon to the atmosphere, but it's really no different than purging a line, and it doesn't really lose much freon. Sometimes you have to do what you have to do to get the air out!

Now that you've got an empty can attached to your manifolds (either evacuated or full of freon gas) and the low-side hose attached to your A/C, open up the low-side valve to pressurize the can. Then place the can in an ice bath. Freon will immediately start condensing inside the can, creating a relative vacuum that will continue drawing freon across. You will eventually be able to fill the can with all of the liquid freon in your system. You'll know when you're done, because you will no longer hear the hiss of freon flowing into the can, and the system pressure will drop rapidly to approx 27 psig (for R12). This pressure is the vapor pressure of R12 at freezing (i.e. in the can). If you want to be even more thorough, collect the R12 when cooling the can with dry ice. Either way, only a trivial amount of freon will be left in your system. You may close off your can and set it aside for later use.

Next, evacuate your system with a vacuum pump. This will rid your system of any air or moisture that might be present. Note: This is an optional step.

Finally, you'll want to recharge your system. Unlike with most topping-off methods, you won't have to guess. Look up the specified capacity for your system (e.g. exactly 2 lb of R12 on a stock 1978 system), and put that amount in. You'll need to weigh your can before it is emptied back in the system and then after it is emptied. The difference, in pounds, is the charge you started with before reclaiming the freon with the can in the ice bath. Figure out how much additional freon you need, and then add it from a new can (using the scale). Don't overcharge. Stop when you've delivered the specified weight.

What to do with the additional freon left in the can? That's an age-old issue. In my experience (and I think the experience of others), those can taps are a bit leaky, and you'll lose the freon over time. You can take the can to an A/C service center and donate the contents. (They should be grateful and not charge you for the donation. If not, go elsewhere.)

~or~

You can greatly reduce the pressure of the contents of the can, so that the rate of leakage isn't so severe. How? Just throw it in the freezer. The leakage rate would be cut to maybe 1/10 that at room temperature. Don't worry about any trace amounts of leaking freon in your fridge, BTW. It's inert.

That's all. I just thought these tips would be useful. I didn't read them anywhere else and just had to invent the methods.

Stay cool!

Sarah

[FastWoman]

One more little note:

We went to the dump today to dispose of a kapoot freezer. There in the metal recycling area, where they deal with discarded appliances, was a pile of exhausted 30 lb freon tanks of assorted varieties. These would of course be less prone to leakage than a 1 lb can with a can tap. I'll be evacuating one of them to store my left-over R134a. Anyway, all it would take is an ice chest and one of those tanks to set yourself up to reclaim freon from your system, be it R12, R134a, or whatever.

[Len]

Hi,

You have offered a lot of ideas on A/C charges. I'd say they are creative and pretty sound. They are also a lot of work and will take time.

Converting the A/C system to a refrigerant gas other than R-12 is probably the best long-term solution. Leaks will occur in old systems and with the very high cost of R12, the cost of conversion will be less than the cost of the R12.

I agree with other posts on this topic, that replacing the drier is critically important. Removing moisture from the system is a high priority. One of the reasons to evacuate the system, before recharging it, is to remove moisture. Never recharge a system without replacing the drier.

Finding leaks in an A/C system is trickey. Sometimes you can spot oil on the lines - since refrigerant oil circulates with the gas, the oil can be a leak indicator.

You can try soapy water, just like looking for a tire leak. Beyond the easy-to-find leaks, it is best to go to a service center which specializes in automotive air conditioning.

When we are dealing with 40-year old parts, there is a good chance that there are so many pin-hole leaks that new parts will be necessary.

When I installed A/C in my 71 Z, I noticed that the compressor was larger than the one for the other 1971 Datsun models. The cabin volume is smaller, so I was not surprised when it really kicked out the cold air.

The only problem I had was with the condensation drain. The plastic hose kinked when it went through the firewall. That did not allow water to drain and the cooling coil would freeze up like an ice cube. I took a piece of copper tubing, carefully curved it and then positioned it inside of the plastic hose to keep the line open.

I hope this is helpful.

Good Luck to all.

Len

[Len]

OK, one more comment.

Without the gauges to measure the pressure on the A/C system, you can still come pretty close to the right charge. As you approach the full charge, the coolant lines will sweat. At full charge, the sweating should go all the way to the compressor. If the top of the compressor is also sweating, then you may have put in too much refrigerant.

Len

[ZCurves]

Sarah, your idea is great and I am tempted to do this myself. The only thing I would be concerned about is the Non-Condensibles that come when evacuating an AC system. That is what those fancy evac systems are all about. I wonder if you could make a filter??