Volvo vnl AC problem, charging the system properly?

Hi guys
I have problem with my AC , it's was leaking from the expansion valve I replace the part and stop leaking , now I tried to charge the system but when I turn the AC ON it goes to low pressure 10psi and when I turn it OF it's goes to full more than 40psi

I put abute 15 ounces , how many ounces I need to charge the system? was full Empty

2015 d13 vnl670
Any idea can help please

 

Here is the sticker on my truck. I believe 1lb of refriderant is equal to 16ozs

20190423_194446 by rhitrucking posted Apr 23, 2019 at 7:46 PM

 

You need to go to a shop. And get Vacuum pressurized.
Watch what they do.
Do not over fill your AC system.

 

Thanks for your answer, Yes you right , so I need to add 3lbs or 48 oz to be fully charges

 

Thank you
Yes I understand, its will be big problem if the system got overcharge

 

The system should be vacuumed to get out all the moisture prior to filling though.

 

That’s normal. Gauge always does that when filling system. If overfilled ( assuming high pressure switch is good) compressor will stay cycled off longer than it stays on, overfilled more it will cycle on and off rapidly, fill it some more and it will cycle off and stay off.A good number if not sure on amount is 35 lbs. Best to not run it too long without properly pulling a vacuum to eliminate moisture, and refilling it. $25 air drier while your at it. Otherwise rust will form and you’ll end up replacing expansion valves again.

 

Don't forget you need to add peg oil otherwise you will be buying a compressor in few months

 

Not for just a recharge, it'll have too much oil

 

One thing I learned the last time I re did my system is. It’s actually better according to Compressor manufacturer ( Sanden) to be a little low on oil than too much. Too much will displace the gas and cause compressor to run hot. The compressor relies on the refrigerant for cooling. Surprised Me as I used to always put a little extra, for bearings I figured. They have different guidelines on their website for how much oil to add for each failure, hose, condenser etc. For compressor replacement they actually say to dump oil out of new compressor and old compressor and the amount that the old one had to the new one. Most of the oil stays in the system, mostly just gas leaks out.. I just got mine fixed. New condensor. Also had a bad low pressure switch, got it jumped now. Then had a loose hose connection, as I was being careful not to break the new one. Finally got cold air as of now. Gonna slap one more can for good luck. When I get home I’ll pull a vacuum and replace drier and put in exactly 5 cans. I’m good to go. Good luck with yours