Car AC topping up

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When topping up a cars AC system (one that still partially functions) with R134a, what is the rule of thumb for knowing how much to put into the system.

[ilbebauck]

There is 'no rule of thumb' for charging an auto a/c ; it has to be accurately metered in making sure you dont contaminate the system with air and moisture when you recharge the system. You dont charge an auto system until the suction line starts to get cold, as that is not an accurate way. Please pay a qualified auto a/c Tech the money to have it done properly, accurately, and safely . A can of R134A under pressure can be dangerous in the wrong hands and should never be sold on the shelf to the general public.

[ilbebauck]

Yes. Anything that is a toxic explosive gas should not be sold on the shelves for the average consumer who most often doesnt know how to use it properly or safely. The only butane I personally would condone on the shelves is the very small container used for refilling a cigarette lighter . Get a shot of shelf-bought liquid R134a in the eye and suddenly that consumer would agree with Me.

[llbeBauck]

The same can be said for religion: Dangerous when fed to uneducated gullible people and should never be sold off the shelf to the general public

[PaxPerPoten]

Using your logic..Perhaps we should outlaw the sale of cars etc. Gasoline is one of the most used flammables that most folks seem to misuse. Either in accidentally burning Homes and Garages down..But not only that.. putting it in cars and killing each other. How about that acetylene stuff.? Mix a bit of Oxygen with it and a spark and you can take out a whole city block. Maybe we can outlaw Dry ice too..That makes a nice urban bomb. Soap and tooth paste should be banned because they contain glycerine.. Helluva an explosive if you get enough of it. ;-p

[ilbebauck]

It makes no logical sense for a Teenager who can buy a 12 oz. can of R134A Freon off the shelf at Walmart, when HVAC Professionals require a Refrigerant Handling Card for correct useage and safety.

[j]

R134a is a single molecule refrigerant, you can top this up.

Assuming you have enough charge to run the compressor (there is a low pressure limit switch), you charge into the suction side to about 40 PSI, at that pressure the suction line should be cold but not freezing. Most cars have expansion devices so the risks from overcharging and slugging the compressor are not great. Put the r134 can (upright) in some warm to hot water and you can charge as a gas.

If the system was almost empty, you would evacuate and if it was empty you'd change the dryer. Then you would weigh in the charge.

If you had the gauges, you might look at the high pressure and look at the subcooling.

Put in a shot of dye so you can find the leak. I won't be following up and you will probably want to take this discussion elsewhere.

[.p.jm.]

Try alt.we.don't.need.no.stinking.gauges

[PaxPerPoten]

I recall no such certification for R134A. I carry a Universal and I see no such requirement in it. Please enlighten me. Not a whole lot of the folks in the HVAC industry use R134A. I however do. Could it be better that a teenager can buy R134A to huff then to cut the Schrader valve locks off their neighbors Central air to gain a plastic bag of Cooling gases to Huff? So the moral of the story is *Keep a tight rein on your Damned Teenager*. Isn't it amazing that we can take a man-child into our military, hand him weaponry, but we cannot trust our Man-child to engage in responsible actions at home?

[Steve]

Maybe its because the military holds the Man-child responsible for their actions, and their parents don't.

[PaxPerPoten]

Could be...

[ilbebauck]

Im referring to EPA certification for refrigerants in general. R134a can be just as dangerous as R410, R22, etc.. in the hands of an inexperienced person. Further, the inexperienced rarely takes precautions of preventing air and moisture from entering the cars a/c system ... even YouTube Videos of Techs showing how to recharge R134a into the system arent purging the hose of air first before letting the freon into the system. 12 oz . cans of R134a should be banned on shelves . And regardless of mom and dad, the Teenager will do and buy whatever he likes since being a Teenager is all about rebellion without the front lobe of the brain being fully developed for common sense, safety, and maturity.

[PaxPerPoten]

Learning from ones mistakes is the best teacher. Being a Teeny-bopper does not automatically give you membership to the Morons club. How long have you had this naggy little old lady syndrome?

[Daniel who wants to know]

Cool, not cold. For R-134a 40PSI=45°F. Add in the necessary 10-15° of suction superheat and now you have a 55-60° suction line. You want the low side to stay as close to 27PSI as possible without going under as

27.7PSI=32°F At 27PSI you will likely frost the bare refrigerant tubing but not the evaporator fins. What is more important is charging to the proper suction superheat or liquid subcooling depending on metering device type. Since cars have ways of controlling the low side suction pressure like variable displacement compressors or clutch cycling switches low side pressure is all but fixed.

Personally I would always use a variable displacement compressor like the GM V5 or V7 and dial in that bad boy via the control valve adjustment till I hit exactly 27PSI @ 2000 engine RPM with a cool interior, the controls on recirc, and the blower on low.

Which dryer, hair or clothes? Perhaps you meant drier.

Probably.

[Gz]

My rule of thumb. I first put thermometer in air vent, fan on low. With Ac off then on, the drop in temp should be at least 40 degrees as your filling. I would also get a input hose adaptor that has a pressure gauge. It shows low and high range. Most systems today have both high and low pressure to computer. The compressor will stop with under or over pressure.

Greg

[Grumpy]

My rule of thumb. I first put thermometer in air vent, fan on low. With Ac off then on, the drop in temp should be at least 40 degrees as your filling. = V8@600RPM, V6@900RPM, V4@ 1100RPM

I would also get a input hose adaptor that has a pressure gauge. It shows low and high range. Most systems today have both high and low pressure to computer. The compressor will stop with under or over pressure.

Greg

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[Gz]

[e-mail]...

Right, rpm matters.

My old system was to watch the sight glass and bubbles.

Greg

[Daniel who wants to know]

I didn't even know outboard motors had air conditioning. LOL. And how do you keep a 2 stroke at exactly 1100 RPM?

[The Daring Dufas]

I seemed to me that in none of the videos were the techs purging the hoses. That struck me as leaving out a very important step. I have a system that I have to service that uses R-404a and some other tech changed out the compressor without replacing the liquid line dryer. I also have a feeling that the system has some air in it. I hate it when I have to go behind someone else who gets hold of one of my customer's systems. My customer called another tech when I was in the hospital with pneumonia which is why I despise those pesky little germs and incompetent techs. ^_^

TDD

[Anti-Spam]

Thanks for that.