Hello. Was seaching but cant find any info about how much pressure should be on high pressure line in bar? The problem is my Jag VDP 1999 4.0 i have changed 3 compressors already.. because all of them was leaking. When i top up with 650g of freon. then run engine and turn on a/c pressure goes up to 15-20 bar. lowspeed fans running all the time.and when accelerating, it goes up to 25 bar and then high speed fan starts spinning. Does anyone know how many bar should be when engine running and when accelerating. and how much exactly freon should i top up ?

 

10.3 - 13.1 bar on the high side. Closer to 10.3 at idle is preferred. You need to know what the low side bar is. All 3 compressors leaking could be from the high side bar being too high.

Are you putting in brand new compressors? Was it a Denso? Are they used compressors?

What happened to the first compressor? I know you said you put 3 in due to all leaking but what about the first? Did it lock up? Did you flush out the entire system?

Need more info to further diagnose your situation.

 

The correct way to add the refrigerant is to measure by WEIGHT. The old R12 system could be filled with pressures and sightglass, but the R134a is very different.

I don't trust pressures while determining refrigerant quantity. You might get close but not really accurate. I have seen 35 on the low side and 220 on the high side but recovered much less than required weight and the system did NOT cool properly. Add too much and a hose might 'pop'?

Modern recovery and recharging machines are the industry standard. Shops don't buy them just to spend money.

Even 'guestimating' an empty system with 12oz cans is better than guessing with a partly filled level and hoping you are close.

 

650g top-up? Do you mean fill the empty system with 650g of freon? Filling with 650-700g is correct.

It is better to replace the receiver drier every time the system is open, unless it is fairly new and the system was left open for just a few hours or the disconnected hoses were plugged if longer. If the receiver-dryer has absorbed too much moisture, it will block the high pressure line.

It is essential to vacuum the system for about 1 hour before filling the freon in order to remove any moisture in the system. Both service ports, low & high, should be used for the vacuuming.

When replacing the compressor, care should be taken not to overfill the system with compressor oil. The system holds 180 ml of oil. The new (or used) compressor must be first thoroughly drained of oil, left to drain overnight at least. Then it should be filled with about 100 ml of oil since the condenser and the evaporator hold about 40 ml each, 80 ml in total.

The too high pressure you are having could be due to the system overfilled with oil, blockage in the receiver-dryer, blockage in the high pressure line to the expansion valve or blockage in the expansion valve. To better diagnose the fault, you need to take both, the low and the high, pressure readings simultaneously. You can then look at the attached PDF file providing possible causes of various cases of abnormal pressure readings. The normal (typical, not specific to Jag) pressures are shown below. The points of fans switching on is as specified for X308.

 

Well first of all when i bought this jag a/c was newer working. So far i have changed dryer(filter) new one, the radiator used one, pressure switch, and 3 compressors. The first one started to leak because my cooling fan was not working so there was too much pressure and blow gasket on the compressor. So now i have 3rd compressor. All the time im taking my jag to shop where they have recharging machine. Firstly they make vacum on system for about 30 min. then charge system with 650g of freon.
And then i start engine. So when engine is started high pressure showing 15bar at (25celsius outside) low-speed fans are spinning. then when i try to accelerate pressure goes up to 20 -24 and high-speed fans start to spin and pressure decreases up tp 15 again. So according to your chart everything is normal ? So maybe problem is those used compressors leaking thats it ?
By the way What about that temperature? How i should know that ambient temperature?

 

The "ambient temperature" stated in the chart is the same thing as what you called "outside" temperature. It is still necessary to read the low (suction) side pressure simultaneously with the high side to be able to conclude whether there is some problem with your AC or not.

 

Ok so today i filled up syatem again .. and guess what the same problem.. again leaking through compressor gasket.
So we filled up system with 50g of oil and with 650g of freon. Then started engine low pressure side was on 3.5-4bar. and high pressure side was 15bar fans was spinning low speed. Then accelerated high pressure side was increasing up to 23and then fast speed fan started spinning pressure deceased about 19. And come back on about 16-18 when stoped accelerating.
Outside temperature was about 27 Celsius but i believe because engine is werry hot so the temperature was much higher.
So im running out of ideas. Thinking maybe those used compressors.. just because they are old and not holding that much of pressure? Or its too much of pressure.. or
i need brand new compressor...
Whats your suggestions?

 

Your low side pressure is way too high. Did you read the PDF file I attached earlier (it is not the same as the pressure chart directly in my post)? The PDF document also shows a case of high low side and high high side pressures and gives possible causes.

 

I have seen your chart. But i don't understand then because according to your chart pressure 3.8is okay on low side?
And high side looks okay as well? According to pdf file all my systems are way too high pressure?
So witch chart should i orentate my self?

 

Go back and reread post 3 above. Have a competent automotive air conditioning/heating specialist evacuate and recharge the system with the correct WEIGHT of refrigerant.

 

Well thats what all the time been done. Im not charging system by my self.. took my car to specialists. And their computer showing that need to charge 650g. They told me what could be the reason of leaking compressor. I have done everything what they told me changed dryer changed switch changed radiator changed 3compressors... So thats why im asking help from you guy's...

 

I think this part of the PDF file applies to the case you are having:


3.8 bar shown could be normal but only for very high ambient temp. According to the other chart, that would be at some 35-38C but you are having it at about 27C when it should be around 3 bar. Perhaps the probable causes shown will help in troubleshooting.

 

If you are blowing out new compressors there is another issue with your system. Denso makes good stuff. Mechanic at dealership who simply swaps parts and hooks system up to an automotive AC charging station does not necessarily know squat about AC systems.

You might want to visit this site where all of the automotive AC geeks tend to hang out ..

https://www.autoacforum.com/

 

UPDATE!
So i went to another ac system professionals. They told me the possible problem. Actually it was mentioned in this thread in that pdf file. So my ac condenser and other parts are old and can have some clogged parts or possibly more oil then it needs. So when they top up my system with 650g of freon thats maximum capacity. But freon expands when it heats up. Maybe my system have some clogged areas and freon dont have any space left for expansion thats thy it goes out through compressor or other joints. So we have tried to fill up system with 500g of freon and it was much better. Low side was about 2bar and high side was 14 and when accelerated goes up to 20 untill fast fan starts to spin. But according to that pdf chart high side is still to high? I want to fix everything before i change another compressor 😀 oh by the way they plugged in obd and checked for system mistakes and found one. They told me that this mistake can be because low pressure on system? Maybe you know more about that?
By the way my ac system blowing cold abou 7 degree celcius. So as i understand it functioning correctly..

 

As the high side pressure depends very much on the temperature the condenser is heated-up to, maybe the fins of your condenser are partially clogged by debris reducing its cooling efficiency. Perhaps a good external wash / backwash can eliminate the high pressure problem.

 

And hopefully you are not using freon R12

 

Freon is correct one. What about that mistake any suggestions?
B1858-Climate control pressure switch circuit failure.

 

You have to use refrigerant R-134a, It is also often called "Freon" but, strictly speaking, it is not. It is correctly called Tetrafluoroethane or "HFC" refrigerant and it requires specific compressor oil and type of seals/o-rings to be used with it. You cannot use Freon-12 (R-12) in the Jag AC system (any AC workshop should know this). As for the pressure switch, it may be faulty and may sometimes switch the High Fans too late causing condenser overheating and too high pressures.

 

Whenever the system pressure is low and the ignition switch is turned ON, the CCM will flag a code related to the Pressure Switch.

 

What I've been doing car ac stuff at work. As a car mechanic. I've seen various high pressure levels at same temperature between different brand of cars. This is normal. But all of them has always been under 3bar at low side. No difference there either 500gr or 1000gr 134a gas systems. Few times i've had high and very high pressures caused by sticking expansion valve. Or just blocked system. The way you describe pressure behavior sounds to me sticking expansion valve. Normally pressure does not raise together with engine speed. 25bar @ 20'c is waaay to high.