Sharing...........

01. The unique nature of R134A is not like regular ambient air/gas. You can not read R134A pressure to verify your car HVAC refrigerant fill level is accurate as per MB spec or
the sticker on your hood or at engine bay.

If our regular/ambient air, it is easy to know fill level and you can tell air weight too, if your scale is very very accurate.
Density of air at sea level is 1,222.5 grams per 1,000 liters of air at 15C. ISO standard.
https://en.wikipedia.org/wiki/Densit...2%20lb/cu%20ft).

Using BAR or millibar is easier, as it is close to 1 Atmosphere. Standard atmosphere at sea level is 1,013.25 millibar or 1.013 BAR
If say a tire is worth 10 liters of air space, 3 BAR or 43.5 PSI worth of air presure simply meant 10 liters x 3 = 30 liters of air is inside the tire, simplified.

A good example is scuba tank of 80CF or 10.6 liters internal volume.
When fully filled to 3,000PSI or 207 BAR, the weight of the air alone inside the tank is worth =
10.6 liters x 207 bar = 2,194 liters , x 1.222kg = 2.68KG or kg to 5.9 lbs....simplified.

Therefore is using AIR as reference we know the "fill" charge by liters or by grams.
This is not the case with R134A in our HVAC. It has to be by weight.

It has to be sucked out ( recovered) and weighted with a scale with 2-5 grams accuracy, thus the filling back ( charging ) can be as accurate to +- 10 grams our of 590 grams
a typical W212 single blower HVAC variant.

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This is nearly empty R134A 30 Lbs cylinder, at 29.x Celsius.
From its 30 lbs content, I have used up like 90% ish. Still it follows its Pressure-Temperature chart. Called PT Chart.



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My car, engine at ambient temperature 29.x Celsius




All within 3 PSI of R134A Pressure-Temperature chart.


Do not mind the interior temperature of 35.x Celsius, my DEHUMIFIER machine is working inside drying the interior.



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What if when you use your car built in refrigerant pressure sensor and your reading is well above , say 14PSI or 1 BAR above the R134A pressure-temperature chart ?
AA. Maybe your engine bay and HVAC systen is not yet to full ambient temperature. Wait minimal 12 hours, better 24 hours.
BB. Your R134A is mixed with air or other non condensable gas or junk/fake refrigerant.

Watch the simplified gas law, when you have other than pure R134A in your HVAC system, video below : ( Ignore the ammonia as refrigerant )



1 is the bad stuff, 2 is the refrigerant, imagine #2 is R134A





Here is a great example of my RECOVERY tank, which has served at least 10+ cars over 2 years and for sure the hoses used, have a bit of ambient air inside them and
possible junk refrigerant on some suspect cars where my friend have gone to an HVAC workshop at least once if not more during the car ownership.



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13.77 BAR is 199 PSI


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This is my baby sized RECOVERY tank, which I only used for 2 of Land Cruiser 300.



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Now, the problem with any recovery machine is, it has hoses. Unless you evacuate/vacuum the hoses and the compressor of the recovery machine down to crazy low micron level,
there is bound to be ambient air a bit inside it. The same goes for RRR machine,which is simply a combo unit of :
AA. Recovery machine

BB. Vacuum pump

CC. R134A container/TANK , a who-re version of a container/TANK as it is filled with all R134A and all alien gas and non-condensable from cars it served ever since its last full vacuuming process of the said
container/TANK.

RRR machine can have it non-condensable gas removed, but can not remove fake or other non R134A refrigerants, only ambient air can be purged and it takes time to do such PURGING.
The RRR machine has to stay still minimum 4 hours, best 24 hours and purge the container/TANK to equal virgin R134A pressure-temperature spec of the ambient temperature ( called PT chart )
https://appiontools.com/content/TB-N...t_Recovery.pdf




I asked my Mentor, Tom Lech : In blue is his reply and in orange is mny additional notes for you guys to understand easier.

"RRR machine can only remove air because air does not mix and become a solution with Ref refrigerant. It’s more like oil and water.. Or more like CO2 and water.
Different saturations ( different refrigerant ) RRR machine cannot get rid of . Some refrigerant will combine with each other and become a new solution at a different pressure than anyone by themselves..
The pressure and the temperature may not be similar to one of the two refrigerant that have mixed and will not lineup with anything on the PT chart .
Any time somebody does not have a refrigerant identifier they’re always left up to luck and chance that they do not get contaminated refrigerant it is only guessing .
When guessing there will always be losses . Because contamination is very common."



So, I hope this explains as to why we cars with R134A HVAC , should never never use pressure as reference of R134A charge being PROPER.


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Something else I want to show you guys.........

Compressor is like our engine piston, it has coompression ratio.
Being a variable displacement compressor, its beauty is variable compression and kind to serpentine belt and engine, in terms of shock loading.
Also in terms of constant liquid line pressure ( HP ), it can be very nice slope and not hill and valley like ordinary magnetic clutch compressor having no variable displacement capability.

Be known that, the lower the liquid line pressure ( HP ) is but HVAC coldness is reached, the better it is for everything.
Good for the HVAC system longevity, good for lower engine load.

Ever since I logged my HVAC with thermocouple using Banks gauge system, I can see its behaviour better.
Too bad I can't connect both my Bank's OBD connector together with Xentry, where I need Xentry to see the command for the control valve of the compressor.
But I do know my compressor typical activation profile or how many milliamps the power commanded byt HVAC computer. I seen often enough.


WILL CONTINUE..................

 

Thank you! Will be helpful for future references!

 

Continue.............

This is April 2023 log. The Xto0l A30M scanner is decent, but it often name component different to Xentry





The time code on top right in green circle is the actual AC compressor ON time.


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Better wind speed from car velocity means your condenser works easier to release heat and HP pressure get lowered., 140.6 PSI only





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This is like a month or so ago in 2025.
Based on Banks thermocouple only.



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See how compressor suffering life is.......... the jump in underhood ( engine bay ) temperature is when coolant thermostat open and radiator start releasing its heat and that heat goes to engine bay.



If one never experience variable compressor operational pressure waveform for HP side ( Liduid / red coupler ) as in logging its waveform,
and uses oldie compressor without variable displacement capabiity pressure guideline, one will get FK-ded because variable displacement compressor can throttle up and down........

Throw away those stupid pressure guideline chart based on oldie fix displacement compressor and start you own logging as reference when your compressor is healthy.

When it comes to variable displacement compressor, each car brand uses its own programming logic, it is not the same. This is the problem.
A Known Good data is good to have.

Remember, FILL R134A for your car BY WEIGHT ONLY !!!!

Have a great COOL day

 

Another fun experiment while I was in the mood......

Zone 1 is R134A tank, virgin R134a all the way to the pressure gauge blue label ( LP ).
Zone 2 is my refrigerant sight tool, its inner tube is worrth approx at best 50 milliliter or air.
I did not vaccum the refrigerant sight tool, I let ambient air to be in there, to be later mixed with R134A.



I open 30 lbs tank and purge Zone 1 to be having virgin R134A.
R134A saturation pressure at 31 celsius is 100 PSI. Gauge is showing 97.7 PSI due to mild purging makes COLD, thus lower pressure.


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I then opened up Zone , which will have ambient air and will be mixed with r134A, the pressure of Zone 2 will be higher than Zone 1 due to the gas law = A + B gas combo.
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I then break apart Zone 1 and Zone 2, separate them and wait till all get stabilized back to room temperature.







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The amount of liquid R134A inside the refrigerant sight glass



All above is an example, R134A fill level inside our HVAC system CAN NOT be measured by pressure, you must weight it.
Any illegal air/gas will throw off your reading. Above is NON compressed state, imagine when compressor is doing its 1 to 5 pressure ratio, 5x more pressure error you get from illegal air/gas.


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TEST 2, is me vacuuming down the refrigerant sight glass to approx 150 microns or lower..





The refrigerant sight glas is "wet", it has compressor oil residue and part of the 99.9% IPA alcohol.
See below the moisture explosion. The hills are the "explosions"




Anyway, took me 20 minutes to vacuum such a small volume of space.

Now, I am ready to flow R134A to Zone 1 and Zone 2, where Zone 2 is almost zero illegas air/gas.


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Now both Zone 1 and Zone 2 can have equal R134A saturation pressure.


Saturation pressure of R134A means it exist in liquid and vapor form at the same time.

The amount of liquid R134A in the sight glass.



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I then separate the Zone 1 and Zone 2.






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The more I touch Zone 2 hardware, the pressure rise a bit because my hand is at 35C easy and R134A reacts to temperature .


0.7 PSI difference only.
Compared to when Zone 2 has illegal air/gas which the difference was 4.6 PSI.
If I have a super stable room temperature and more time, it will be better.


Some video entertainment on why R134A will boil at -26.3C yep becoming steam or gas.
"R-134a has a moderate boiling point of -26.3°C, making it effective for cooling applications. It has a high latent heat of vaporization, allowing it to absorb significant heat energy before evaporating. It operates at moderate pressures, making it relatively safe compared to high-pressure refrigerants like R-410A."



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R134A PT chart attached

 

To post simpler solution, when I grew up in place, where AC was unknown, moving to CA forced me to accelerated learning curve.
So for last 40 years, I keep all my AC freezing my elbows, even in 120F weather, while I never used a scale.
Just last week, after 12 years my E250 become low on refrigerant.
I have AC manifold and 30 lb tank of r134, but don't like to disturb high-pressure fitting, when I have the same value available on scanner.
So hooked up low side to the tank and was observing high pressure and evaporator on scanner..
Here is initial data, where AC was still cooling some, but not enough.



So opened the charging valves and was observing the high pressure + evaporator temp.
You have to go very slow, as refrigerant is charged in liquid stage, when it vaporize in the system, what will jump the pressure. You don't want to overcharge the system, who has about 30 bars high limit switch.
So here is how the data looks after charging.
I've got evaporator temp down to 1.9C, but at this point anti-freeze limit kicked and put it in 3-4C operating temp.
11.4 bars is the high pressure at stabilized temp and it goes into about 20bars when system kicks at max.



I noticed 2 outside temp readings, who show quite big difference.
I think 1 might be the sensor in the grill, the other in MAF, but since the system is freezing my elbows again, I am not going to spend my time to investigate it.

 

Your method is do-able, but it is not accurate. Even at 100 grams less than the specified 590 grams, due to variable displacement compressor being used, the pressures both LP and HP can be within "limits".
Some HVAC system can be fillled using subcooling and superheat method using pressure gauge and temperature sensors at specified location.

Its you car, you can do what you like to it.
But I suggest you adapt to using scale to weight the refrigerant, when and if it is specified at 590 grams R134A ( single evap W212 ).
The mass of the 590 grams of refrigerant will make sure the compressor oil is circulated properly within the HVAC system.
Too little R134A, your EVAP will have lots of compressor oil kinda stuck there.

Also to note high humidity country like mine, while maximum is usually 95F / 35C, my humidity of 85% or more is much heavier on HVAC load compared to 120F Vegas with 30% average humidity.
Cooling down by 1F degree of air of 1 pound weight is only requiring 0.24 BTU, this is sensible heat.
To condense the water vapor in humid air to become liquid water is 970 BTU per 1 pound of water.
So unlucky for me, my HVAC power much first cater to fighting humidity by taking its latent heat .
I am sure you learnt of latent heat and sensible heat in your HVAC training.

 

Hi Kajtek1,

Your method is simple and can use almost in Japan car, but you'll never know how much Gas in your system. R134a can work if it has 25% less in system with no diffirent, or 10-15% more, you can't know it. If less or more gas in your system, your A/c will work as normal but the life of the system will be reduced. So charge R134a with weight is safe.

The outside temp and outside temp sensor as I know is temp of sensor on grill and temp calculate of ECU. I think it very stupid by Mercedes. In my situation: My car in park in B2 parking garage, and temp is only 26 deg C. And outside temp is about 40 deg C. When you runout from B2 parking, Temp calculate by ECU will not increase by outside temp, maybe ECU think that the temp sensor 40 deg C is affected of engine temp, so your A/c will not work hard. And when you run a bout 40km/h for about 1 Km to take ECU know that real outside temp, so the temp calculate by ECU will increase and your A/c will work as they should. So very stupid and complicate.

 

For me the accuracy is good enough, when I have frozen elbows in 110F weather.
As per system tolerance, this is the 1st time I had to touch AC on W212, but having several W210 in family, I work on them quite a bit.
Their system was rated for 1 kg of refrigerant, yet for testing I could get it started on single can, or 360 grams. of it. It would cycle with such low volume, but still deliver some cooling.
As for overcharge, the high limit switch is about 30 bars. I experienced that and the effect is that the compressor will come to this pressure within couple of seconds and then the switch cuts it off for like 10-15 seconds, before pressure lowers and it starts pumping again.
The result is basically no cooling, but again, the symptoms very easy to catch.
I am still missing climatronics on W210 and W211, where I could display AC values and troubleshoot it at 75 mph.
Even I drive my Bluetecs with ScanGauge3 for monitoring, it will not show AC values.
BTW 120F in Las Vegas comes with single digit humidity and some people suffer from dry air. I am using swamp coolers in my house, what keeps humidity about 50%. Suppose min 40% is healthy air.

 

Below pressure readings of my 2010 E550 A/C running well in 90F ambient temp. Low side 34psi, high side 190psi.

A lot of talk about the fill amount as grams of refrigerant but we need to remember that the principle of the A/C system IS change in pressure and phase of the refrigerant. Fill level in grams gives you the “ball park” value and allows the system to work but fine tuning it is by pressures in high and low sides of the compressor.

As a detail I remember that low side pressure during this test was at very close to max as at 36psi the cooling started to suffer.

 

It's desirable to make A/C work by not precisely measuring a sealed system for free without robbery charges.

The factory fill procedure is the most accurate but not always practical in the field on the go.

Some ppl have reported less than factory refrigerant works better ie. it's overfilled for cold countries pressures.

The way most "factory setup" miss the mark, it's a real good idea to play with it. Refrigerant weight is not carved in stone measure (less is better!)

W212 uses TXV to regulate evap. coil temperature and variable rate compressor to regulate high side pressure. Yet what we really care about is low side pressure... even the AAC module totally ignores.

Compressor pumps down low side gas into high side hot liquid side. As compressor ages it's less able to buildup pressure difference and benefit from less load.


Given high summer heat... :

• Standard fill is about ~190/30
• lower fill would do 170/20
• higher fill would do 210/40
• an old compressor 150/60

Earlier we saw that when we keep 200°F engine heat out of the high/low side, system is more efficient at cooling in traffic jam situation. With less heat working pressures remain lower.

So wrap your A/C lines and don't overfill to stay near efficient pressures.

 

General rules are that 3% AC charge loss in a year is acceptable, so I guess factory spec allow for overcharging, so the car will not come back during warranty.
Still I just helped a friend with his 22 years old C-class. He says it was 1st time he serviced AC in its life.
Black car driven in 120F weather, although not that many miles.
My W212 needed recharge at 10 years mark.

 

How about we collectively start recording static refrigerant pressure vs. ambient temp.


This should give us a ballpark charge indication:
low - normal - high.


With that number ppl can decide what to do.

 

I remember in the 1960s and 1970s that people in the southwest would strap burlap bags full of water to the front of their grill to help cool the radiator through evaporative cooling as the water would slowly soak the bags. Do you guys still do that?

 

Toyota GR Yaris has water spray and bottle for this purpose, for their aftercooler Heat Exchanger.






https://easycars.jp/product/intercoo...-for-gr-yaris/