There were some growing pains when the R-12 was obsoleted.
R-12 had decent capacity to transport heat, and carried mineral oil well. R-132a works at similar pressures but carries a bit less heat, and is incompatible with mineral oil. It works OK with PAG oil, but is especially critical to get all the water out of the system…not good with R-12/mineral oil, but a bigger issue with R-132a/PAG.
A mechanical vacuum gauge doesn’t have enough resolution at the low pressure end to distinguish between a dry system and a wet system, even if you correct for altitude and barometric pressure. You need a thermocouple or Pirani gauge for that, and very few automotive techs invest in those, and even many HVAC tech try to get by without. R-12 systems could tolerate a little bit of water, so years of experience taught automotive techs that mechanical charging gauges were good enough when evacuating a system. This lead to a lot of poor outcomes when R-132a arrived on the scene. Hopefully the word has spread.
R-134 also works with Ester oil, which will mix with any left over mineral oil in an R-12 conversion. Not a problem.
Umm, sorry but you are wrong here. At 75F 20" of vacuum will boil off any water in the system. Any decent vacuum pump for AC use is capable of pulling 29"+ of vacuum. So you evacuate the system for 45 minutes or so. Shut off the valves and watch the gauges for a couple of minutes. If the vac holds at 29" or so, no water. If the vac drops to 20" or so water.
Frankly if you can tell the difference between 20" and 29" on your gauge set, you need some new (better) equipment.
This ain’t rocket surgery.
The push for more environmentally friendly refrigerants (zero ozone depletion potential and lower global warming potential) has resulted in refrigerants that are less efficient than previous refrigerants, however even bigger improvements in equipment efficiencies have offset this and have generally resulted in more energy efficient air conditioning systems - at least for building air conditioning. I’m not familiar with the details for car air conditioning.
I had to do some searching to find a cite that is not a crude graph with room temp buried in the noise at the bottom. The table cited above gives boiling points for water at 70,000 and 80,000’MSL as 82.9F and 67.3F respectivly, bracketing your 75F value. From the same table, this corresponds to 1.32 to .82"Hg(absolute). At sea level, a 20"Hg(gauge) reading is about 9.6"Hg(absolute). So the absolute pressure is about an order of magnitude too high to boil water. If you want to boil water at room temp, you need to get down to around 1"Hg absolute or around 28.6"Hg(gauge). If you have significant water, though, you will cool it, possibly even freeze it by doing so, and it can take a long time to boil/sublimate it off.
Normal atmospheric pressure variation can account for about 2.75" of variation at sea level. That is more than twice times the difference between outer-space/near perfect vacuum, and having a just good enough pump to get the job done, and more than enough to make things look wonky depending on the weather that day if not accounted for, and yet I have never known any refrigeration tech to consult a barometer.
But I think the greatest cause of my bias is that I have only lived in Denver and Albuquerque, so always above 5000’MSL, so right at 5"Hg difference give or take. I have looked at a lot of AC manuals, only only the engineering type stuff bothers to mention the importance of altitude. The literature aimed at service techs, and especially automotive, rarely seem to mention it, and then only in passing. I’m sure some must emphasis the importance, but not that I have seen. This results in a lot of techs at high altitude (the only ones I have any experience with) that just assume all the books are wrong, because they have never seen any pump pull more than 24"+/- vacuum, because they won’t. I have met plenty of engineers don’t seem to grock absolute pressure vs. gauge pressure…so I can see why literature aimed at wrench twisters doesn’t pursue the point.
So anyway, my love of thermocouple gauges probably comes from the fact that they read absolute pressure, so it doesn’t matter where I am or what the weather is doing that day. If the national labs around here didn’t keep stocking the surplus stores with them though, I’d probably be too cheap to buy one new.
[QUOTE=Snnipe 70E]
On an auto AC compressor can the seal hold under a high vacumn?
[/QUOTE]
Sure. They are not a simple lip seal, which due tend to favor one direction or the other for containing pressure. Instead they have a graphite face under spring pressure running on a bronze plate usually. The materials have a high polish, and any leakage allows a trace of oil into the interface, which stops the leak. This is usually referred to as a mechanical seal. Of course the do seep a little over time, but many cars will go a decade or more without topping off the charge.
The seal only has to hold atmospheric pressure regardless the quality of the vacuum pulled for evacuation. There is only about a half psi difference between a weak vacuum not even usable for a Dewar (thermos bottle) and a perfect vacuum.
I still have a hard time believing the efficiencies of todays equipment. In my buildings I have a old sidewinder about what 3 KW per ton. And a turbocore around .28 KW per ton.
If any student in my thermo or reffer classes claimed that some day we would have machines with these efficiencies they would have failed.
I have, apparently, ticked off some posters here who are qualified HVAC people, and/or, educated in Thermodynamics well enough that they can speak lucidly about the subject, “why don’t today’s refrigerants work as well as Freon?”. I simply pointed out, among other comments, that part of the problem is the perception fostered by tradespeople out to make a quick buck and posited that all HVAC people should be held to a high standard, an opinion shared by others.
How anyone thinks this is an attempt to hijack a thread? Ridiculous.
the OP is well advised to listen to the folks here describing the fact that HVAC systems, today, are far more efficient than anything dreamed of in the past. They are, too, far more expensive and complex, and when they fail, often must be repaired or replaced at a very high cost. This can create a situation where the OP thinks the stuff today is inferior to that of yesterday. 't’aint so, but it is easy to think such when the bill comes due.
Well I used to do a demo in AC class. Two flasks of water on at room temp or so the other cold out of the fountain. Corks in the necks of both hooked to an AC vac pump. One flask would merrily boil away, the other would just sit there.
I would ask the students why the one does not boil?
In any event getting the water in an automotive AC system warm to temps well over 100f is about as easy as falling off a log.
It’s called start the engine, and turn on the heater. The engine will heat up the under hood stuff and the heater does a wonderful job on the items inside the car.
About your freezing comment. The likely hood of having more than a couple of drops of water in the system at any one time is frankly slim to none. So the chance of that water freezing before it can boil off is right up with the odds of your room temperature going down because you brought a cold can of beer into the room. To much heat laying around looking to move to something cooler.
Also if you are doing AC repair when it is cold you aren’t going to freeze shit with a couple of hundred horsepower throwing off heat.
You also forgot to account for the lowering of the boiling point of water at altitude.
I stand by my comments.
I used to be very conversant in the matter of how much absolute pressure in a vacuum space was created by the moisture therein. We pulled vacuums on cryogenic containers down to very low numbers…10 microns or less for completely dry, very clean spaces… but frequently needed to pull down to about 1000 microns because some water was still being boiled off by the vacuum, then watch the number go shooting down to near zero when we put a cryogenic fluid into the inner container. Add to that, we had molecular sieve ‘packages’ taped to the inner container so that the material, at liquid helium or liquid hydrogen related temperatures, would snarf up any remaining molecules of oxygen, nitrogen or argon.
At its best, a liquid hydrogen tank car could be shipped from California on the Santa Fe, and arrive in Chicago 5 days later with only an increase of a a few psi in the pressure inside the container, representing a heat leak so small that it could be called ‘insignificant’.
One of the odd and tragic consequences of using those absorptive packages inside the vacuum space came when a liquid oxygen portable container might be dropped, breaking a line inside the vacuum space. The oxygen would combine with the hydrogen absorbed by those particular packages and produce an explosion, one that included the steel of the container being explosively combined with the 100% oxygen atmosphere. Instant death for anyone nearby. The hydrogen came from the gases that would eminate from the welded seams of the container. Later changes in manufacturing technique made this type of accident impossible.
Anyway, my opinion on the matter of pumping the moisture out of a car’s A/C system is that it isn’t difficult with any sort of decent pump, but fresh lubricant can also help if no progress is being made. Sometimes the pump isn’t cleaning up its lubricant, getting rid of the moisture, properly.
I know you are angry that I warn people about dishonest tradesmen. Why? You know they exist and that there are some shops that don’t know how to do the job properly and which haven’t the right equipment. What I’m mentioning, in one case, is a shop like that, a little garage that hired a guy who said he was an expert, but who proved with my car that he was not… In the other case I mentioned, the shop was a tire dealer with major advertising about their top-notch A/C equipment. They used all sorts of sensing devices, figured there must be a major problem, a big leak, maybe the compressor seals, and, without once looking at a snap together connection that was, somehow, loose (or they had loosened it?) , tossed a big estimate at me.
Who do you trust? I always trusted AAA, thought they were really an example of highclass honest behavior, until a few months ago when my car came due for inspection. The day i went in, there were no other cars being worked on. The manager and two ‘inspectors’ returned to the waiting area with the bad news…I needed $2300 of work to get the car to pass inspection. My power steering rack and pinion was leaking, and needed to be replaced. My shock absorbers/struts were in horrible condition, and my brakes needed a major rebuild.
So, I took the car to another shop for a different opinion. I asked them to show me any oil or hydraulic leaks they could find. I asked them to evaluate all the shocks, and to remove the wheels to expose the brakes pads and shoes, so we could examine them together.
their findings? No deficiencies, passed, no work recommended. No leaks, no bounce, no particular wear on the pads and shoes I had installed myself about a year ago.
AAA. Can you imagine?
HVAC work is often very expensive. Often, if a newer unit needs work, the parts are very expensive. But, I’ve seen a compressor replaced in a unit where one outfit wanted $1200 to replace it, and I got it done by checking the price and hiring a contractor to simply install the unit I bought, for less than $400, including a new charge. (that was an older unit, of course). Whenever a contractor or service organization tells me, “that’s the going rate for that ________”, I look it up myself.
Another case. Accident damage to a headlight assembly. Highly recommended shop offered to replace the assembly with a used one for $200. I bought a new one on eBay and replaced it in twenty minutes, for $60. Where is the honesty, the integrity?
Every consumer should behave in the fashion that if 'you want my business, show me I can trust you. Show me your recommendations and training certs. Tell me your markup percentage on parts. Tell me how handsome I am and that I look like I will live forever," and you might get my work, if you still want it.:):)
I am not aware that ammonia burns. But it is very poisonous. Some time in the 20s, an entire German family was asphyxiated when their ammonia refrigerator leaked. Einstein was so disturbed by this that he and Leo Szilard invented a refrigerator that had no working fluid, but somehow used some kind of sound vibration to do the cooling. I don’t understand it myself. In the meantime Freon was discovered and seemed perfect. Non-inflammable, non-poisonous, etc. Who knew it would destroy the ozone layer?
And, BTW, that last statement is as well-established as, say, global warming or evolution. The best evidence is how the ozone layer has been gradually reestablishing since the use of Freon and related gases was sharply curtailed.
I wonder whether the Einstein-Szilard process could actually work for modern refrigerators and freezers. Especially the latter since nearly all refrigerators sold today have substantial freezer compartments.
I’m not sure if I am adding to a high jack or not but there seem to be many posts about this.
It is buyer beware. There are many crooks in the repair business out there and A/C Refrigeration is no exception.
I worked as an A/C Refrig tech for 20 years (left the trade in 1992 so am not up to date on the latest in technology).
I worked for Sears. You didn’t have to be the greatest mechanic, but it was important that you be personable and VERY important that you be honest with the customer.
I remember many many times when a customer would call an independent for a Sears product because it was said that Sears was too expensive and when he would finally call Sears, because it wasn’t fixed, I would find a basket case due to sheer incompetence and greed.
The worst cases were when the customer told me the last guy added freon to the refrig because he knew it was low and charged him a couple hundred dollars. Added refrigerant to a sealed system? I knew I was In trouble and so was the customer.
Sure enough I would pull the back panel and there would be a ball of ice on top of the compressor and a cheapie tap-a-line on the suction side. So you’ve got a contaminated system. …tap-a-lines are notorious for leaking. And the real problem was something simple, like a bad defrost timer…which Sears would have replaced for under $50.
Somehow techs did not know that Whirlpool (and older Frigidaires) used rotary compressors…Which would take forever to develop a frost pattern compared to piston types…and acted like being low on refrigerant for up to an hour after being shut off for a few hours.
I would charge the customer the $9.95 condemn charge and tell him it wasn’t worth fixing. We charged about $200 to evacuate and reseal the system plus whatever the cost of the real repair.
Many many other similar stories, won’t bore you with them all.
Yes ammonia is combustible. But the range where it will burn is narrow.
A family asphyxiated by a leak in a refrigerator? must have been really small house or extremely large unit. Also I can not imanage someone sleeping through a leak in a ammonia frig.
Are you sure that it wasn’t a different refrigerant than ammonia?
As I recall methyl chloride ( ??..not sure if that was the right name for it) was a commonly used refrigerant in the early years and it was real nasty stuff if it leaked in an enclosed area. Old story I heard was that a reefer leaked it out next to an open window and killed the tree outside.
