Can someone smart walk me through AC recharging?

[jonathan909]

Here's the story to date:  It's the '01 H6 OBW I've been working on over the past year.  Everything's been going pretty well, so (since it just got hotter than hell here) it's time to move on to the AC, which hasn't worked since I got it.  Thinking it's stupid and wasteful to use a can of refrigerant+dye to find a leak I know is there (I pulled a vacuum and it went away pretty quickly), I made up an adapter from my shop air to the manifold gauge.  (Please skip the lecture about moisture in the system - I understand, one thing at a time, let's move on.)  Took a minute to find bad O-rings on both sides of the compressor.  With them replaced, the system holds a vacuum just fine.

Now comes the tricky part:  Every instructional youtube vid claims "here's how the pros do it!" when we all know the pros don't use little retail cans of refrigerant.  I got a big tank so my pals and I can do this at a fraction of the cost.  The downside is that this makes it a lot harder to add the specified amount of refrigerant by weight.  Also, being in Greater Upper Soviet Canuckistan, we don't have R134a up here - it's illegal.  We have R12a.  It's compatible with R134a systems, but if you mix the refrigerants you seize the compressor in a heartbeat.  So I added "some" refrigerant to the (evacuated) system today, and it's running detectably cool, but not cold.

So what am I doing wrong, besides not knowing how much I've got in there?  Should I be feeding in liquid or vapour (the tank has a valve for each)?  How can I get the charge right without relying on a scale?  Presumably I should be able to suss this from the gauges.  Someone please set me straight.

Edited June 3, 2021 by jonathan909

[1 Lucky Texan]

Man, I could not even find a good video on using manifold gauges. I use the them for vacuum application and charging, etc. But the whole pressure ratio thing is hard to discern for me.

I can tell you, the system can make a 'hooting' noise if it is overcharged so, there's that. It is sometimes helpful to use a box fan to blow into the radiator too I think.

[idosubaru]

Sounds like it’s too little.  It’s cool but not cold abs the compressor cycles on and off. Id just add some more.

got a left over/old cheap auto parts store cans that come with cheap simple gauges with too little-correct-over or whatever colored gauge?  They work well enough to get it cold 

it’s always those two orings on that car. Fixed a ton of them. 

[Numbchux]

The pros do not use gauges, only by weight.

 

I work at an equipment dealer, where we do some A/C work. Not enough to justify a $1000+ machine. We buy 12oz cans instead of a keg, specifically for accuracy. If you're going to use a keg, you should at least have a scale to weigh it accurately.

[idosubaru]

47 minutes ago, Numbchux said:

The pros do not use gauges, only by weight.

 

I work at an equipment dealer, where we do some A/C work. Not enough to justify a $1000+ machine. We buy 12oz cans instead of a keg, specifically for accuracy. If you're going to use a keg, you should at least have a scale to weigh it accurately.

+1

I got a case of cans for like $5 and use two cans per Subaru.  Wash rinse repeat every time. 

[jonathan909]

Interesting.  Counterintuitive.  Would have been good to know before buying the keg, of course, but there was/is still a strong cost-effectiveness argument for having done so (assuming we can figure out how to use it).  I have a digital shipping scale, so that might end up being useful.

Until I can work out the weight approach (one part of which is going to be resolving the behavioural differences between R134a and R12a), I'm looking at temperature/pressure tables to get a handle on the behaviour of a correctly-charged system.  It would seem to make sense, then, to just add refrigerant until the system kinda falls into line with the tables.

Edited June 4, 2021 by jonathan909

[idosubaru]

Yeah gauges and all is beyond our need most of the time for Subarus.  Your refrigerant availability may be better and/or worse than us in the US. 

[jonathan909]

But the gauges are part of the package (i.e. "manifold gauge"), so we've got 'em and might as well understand how to use 'em, right?  And as with most things up here, usually different (e.g. R12a vs. R134a) and/or worse (e.g. more expensive and sometimes just a lot harder to get).  Rarely better.

[idosubaru]

Yes sir. I’ve got the gauges just in case I need them like you. I learned on them 15 years ago and haven’t needed them/forgot about them since. But their they’re if I need to relearn the ropes like you need to right now.  I’d just be asking and poking around like you. 

[el_freddo]

How is it that r134a is illegal but you can freely get and legally use Ozone damaging R12A?? Crazy! 

There’s also a sight glass in one of the lines. We used LPG or hichill in my L series (changed all the O rings to be compliant). When running, you should see a continuous stream of tiny bubbles flowing through the sight glass. Don’t know how different it looks with other refrigerants. 

If you have access to another Subaru with working AC, you could check out that sight glass activity and try your best to match that. 

Cheers 

Bennie

[idosubaru]

4 minutes ago, el_freddo said:

How is it that r134a is illegal but you can freely get and legally use Ozone damaging R12A?? Crazy! 

He’s in Canada and I think some industries can still get it for legacy (old) equipment in the US but it’s pricey usually here. 

It may be damaging on an individual basis, but large scale is different and not that simple.  retrofitting every AC system in the US would be problematic and not environmentally advantageous over a slower roll out of new refrigerant. New equipment, supplies, travel, logistics, costs, manufacturing costs, and ramping up for inordinate one time production, and labor are an environmental disaster too. 

134a is nice but asking companies to produce enough to retrofit every US unit in a short period of time requires manufacturing, delivery, storage, etc. and companies would have to ramp up for a huge 1-3 year supply boost and prepare for a HUGE let down when it’s all done. That’s a manufacturing and logistics nightmare. 

Slow phase outs and roll outs are economically viable, and imperfect but reasonable environmentally as well. 

[jonathan909]

Well, it's complicated...

https://en.wikipedia.org/wiki/HC-12a

It's not just about ozone anymore - we pretty much solved that problem, so now it's about greenhouse gasses.  But it's also about safety, which is why R12a is illegal in the US.

There are exceptions to all these rules, of course, but they have to do with industrial users vs. consumers and whether you have to get a license to buy it and crap like that.

[nvu]

Scale method is simplest since you already got the cylinder.  Just figure out how many oz hc-12a is equivalent to r134a and always start from vacuum.  Put the cylinder upsidedown on the scale, with the engine off, run the liquid into the high side and get close to final weight. (Edit: Precharge from the high side with engine off always.  Make very sure the high side manifold is closed tightly before starting the AC.)

Flip over the cylinder and start the a/c.  You can ease into the final weight from the low side with the a/c running.  

With no scale and gauge only it's too easy to overfill a system and ruin the compressor.  Especially if the compressor was already worn and you thought the gauges read correctly at 1500rpm per service manual.  The system could be overcharged to get a good reading and the next time you rev the compressor locks out.

Looking around the web,  one site selling it says, "One 6 ounce can of FrostyCool 12a Refrigerant is equivalent to 15 oz. of HFC-134a & 17 oz. of CFC-R12."  Guessing most subarus use around 17oz r134a,  you'd need to add 6.8oz HC-12a

Edited June 6, 2021 by nvu

[el_freddo]

On 6/5/2021 at 9:25 AM, idosubaru said:

Slow phase outs and roll outs are economically viable, and imperfect but reasonable environmentally as well. 

Thats how It was done over here. If equipment ran with the R12A then that’s all good. Once recharge was required, if the AC service person had R12A in stock they could use it. If not the system had to be changed over. 

This is why I find it surprising that it’s still available. AFAIK our change over of old equipment/these requirements came in to effect a good thirty years ago. 

I know that R12A is preferred over R134A for refrigeration. And from what I’ve only heard around the traps, they say that R1341A is very damaging in terms of climate change stuff. 

Anyway, that’s quite off topic, I was just really surprised to hear that you could still buy R12A. 

Cheers 

Bennie

[jonathan909]

1 hour ago, el_freddo said:

Anyway, that’s quite off topic, I was just really surprised to hear that you could still buy R12A. 

Hell, I'm surprised that Canada and Oz aren't aligned on this.

[idosubaru]

3 hours ago, el_freddo said:

Anyway, that’s quite off topic, I was just really surprised to hear that you could still buy R12A. 

Cheers 

Bennie

I see what you mean, yeah I’d never expect to see it again here. It’s archaic now. 

[GeneralDisorder]

R12 is out there for sale. Current pricing is about $2000 for a 30lb cylinder. I know where I could lay hands on about 120lb of the stuff for the price of asking. It's not as rare as you might think. 

As for filling R134 - it's done by weight. When that isn't appropriate or possible it's done by system pressure which varies based on ambient conditions. It's not that difficult really. 

Being a shop owner I invested in a $4,000 AC machine so I can have my joe's recharge systems and be fully compliant with the laws of the land. Don't wish to engage in any imperial entanglements over not properly recovering refrigerants. 

GD