Do you know that you have any leaks ?
R12 does not have oil inside the can UNLESS it says it does... it will say ' OIL CHARGE' on those that have oil added...
You do not want too much oil... very bad...

You really want to vacuum even before just putting in stuff to check for a leak.... because the r12/oil and moisture mix and cause corrosion and acid to be in the system...

So try to vacuum to boil off water.... and it will help you decide if you have a big leak....

Check out the " alternatives to r12" thread... about 4500 viewings... and we go through almost everything about why the proper procedure is so important...

What most people fail to recognize is how severe an environment the inside of an AC system is... and how hard a car ac has to work compared to a home system... your car is a rolling greenhouse basically.... so lots of glass...and wind going across it... tough place to perform..

Carl, If you did jump the compressor and put a can of r12 in.. how are you going to find the leak ? Do you have a sniffer ? One problem with just adding the R12 is that usually a leak took oil with the R12 out of the system... so you are taking a chance on running it low on oil.... low or high on oil is very bad.... We do not recommend using leak finder in the system... often gums up tiny holes which need to be open.. like the TXValve...

Those pictures make it look like rocket science, it ain't.

The charge by weight instructions are great on the assembly line and fine with warranty repairs on nearly new cars. After anything is changed that affects the internal volume of the system, the required weight changes.

A weight scale is no easier to come by than a temperature gauge. If you check the temperatures on the appropriate parts of the system and compare them to the temperature scale on the refrigeration gauges, you can tell if the system is performing correctly.

If superheat is inadequate and liquid refrigerant is entering the compressor, bad news. One example of a serious problem that can be avoided.

There is no substitute for understanding the system you are working with.

"A weight scale is no easier to come by than a temperature gauge. If you check the temperatures on the appropriate parts of the system and compare them to the temperature scale on the refrigeration gauges, you can tell if the system is performing correctly."--TwitchKitty

The books say weigh the charge... why are you making it more complicated than they do while claiming it is simpler than the book passages which I have posted ?

It sounds like you are saying one needs one of those non contact infrared thermometers.... ??? If not, then how is the temperature checked at those points ???
And tell us exactly where those "points" are, please. Because I have never seen this information offered in any of my manuals or by anyone on any AC or MB forum.

I would guess that half way down the condensor would be a changeover line.... but don't know what else to look for on the back side....

I will have to look again..... but was not aware of temperature scales on my refrigeration gauges....I only have high and low side guages for R12 and R134a.....

I do have some very hard to read charts in my AC manual ....

Yes, but those same manuals that explain how to charge an empty and evacuated systems by weight, also have instructions on using a thermometer near the condensor and another in the vent and how these temperatures relate to the low and high pressures. The manuals also give the necessary temperature/pressure relationship informtion.

I expect that beyond the factory, there have been more a/c systems successfully charged by pressure and temperature than have been done by weight or volume.

I am not saying that using thermometers and gauges is a better method than charging an empty system by weight. It is not. It is, however, an acceptable method for getting the charge close enough for system health and effectiveness.

I am not speaking of correct oil amount, that is an additional issue.

Have a great day,

Larry, I have not run across that info....
I only have three AC manuals... the MB , one General ac with one chapter on Auto AC.. and one manual just on AutoAC....
I may have just missed that info... but would be surprised to find that IN my manuals... I have perused them alot..

So how about posting the specifics of using a thermometer and temperatures to check your charging progress ?

Is this one of those times that the non contact infrared laser thermometers is the best thing to have ? I have been looking for an excuse to get one....

If you don't have one of those... do you tape a regular thermometer to those items ? And where exactly do they suggest they be placed/taped or whatever ?
Thanks,

You are kinda asking for a short course on AC. Here is a link to one, I am sure there are better, but this looks pretty straightforward at a glance. Read the part on subcool and superheat. Edit: Then read the section on charging the system.

The infrared thermometers are good on some surfaces and not on others, I want to buy one too. I am using a probe that I hook up to my multimeter. I needed it one day and bought it (edit: the meter and the probes) from sears for about $100, the probes are extra. I would have probably bought the meter from somewhere else if I had taken the time. Edit: I bought two probes, an immersion probe that I use for air temps and a surface probe that I use for surfaces.

This course says don't use the saturation scale on the gauges, once you compare it to the charts and get a feel for it, you can use it.


PDF version

Here is another more involved paper.
EVALUATING AIR CONDITIONING PROBLEMS

Thanks, will go study it....

Probe = Thermocouple ?
what stock number ?
how does it stick to the surface ? tape, magnetic ?
Where on your car do you stick it ? Do you only have one for the mechanical stuff.....and then one for the air temp ?

I just use cheap old Dial Thermometers. If you only have one it will work. Put it somewhere in front of the condensor. Setting on something a foot or two in front of the condensor with the probe in the air for a few minutes will work. Note ambient (condensor air temp.) Then put it in the vent.

I also have a simple thermocouple for a DMM, but I don't bother using it for this work. The dial thermometers are plenty accurate enough with good enough resolution.

One source of charging and performance information is the "Master Cool Automotive Air Conditioning Basic Service Manual." Begin on page 99.

Have a great day,

I understand about using ambient temperature as a reference ...
But I thought TwitchKitty was talking about something on the order of those temperature strips which are used for showing the amount of propane remaining in a tank.....and also if one were trying to determine if you have mixed gases when you have evacuated a system....
It sounded like he meant some way to tell exactly where, from the outside, the lines between liquid and vapor refrigerant occured....as a help to determining when one had the proper amount..
Which of course interested me because of my consideration of placing two Reciever Dryers in my system... which would change the amount of R12 which would be proper since the system inside was being increased...
If so, I would like to know where exactly this thermometer is to be placed... I would think half way down the condensor ... but can't figure out the other place because the action is happening inside the evaporator....
I have the pocket thermometer which most AC people use... which will stick in the vent and show on its face....

After the questions in your last post I have to assume that you haven't read the mentioned sections in the Air Force course. It is a quick read and should answer your questions.

You probably already know the answers anyway, you just don't know that you know them, HA.