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2004 X3 - Pag oil moisture concern, oil amount

piperflyer on Mon July 12, 2010 6:26 PM User is offline

Year: 2004
Make: BMW
Model: X3
Engine Size: 3.0L
Refrigerant Type: R134a
Ambient Temp: 95F
Pressure Low: 14.7
Pressure High: 14.7
Country of Origin: United States

I searched around in the forums (lots of good info!) but could not find enough specific information to answer my questions, so I decided to join and post. FYI...I also have purchased and looked through both the Haynes A/C Techbook and the Mastercool Automotive A/C Repair Manual looking for guidance.

Background: Three years ago the system leaked out. Leak was traced to the evaporator. I replaced the evaporator and TXV with new OEM parts and the receiver dryer with an aftermarket part. At that time I evacuated the system and recharged with 134a. I based the refrig charge on system pressures. The A/C worked fine for ~ 2 years. (note: I did not add any oil since I did not touch the compressor)

In September of last year the system leaked down again. I again traced it to the evaporator and recently (for the second time...) replaced it with yet another OEM evaporator from BMW. I will be replacing the receiver/dryer (with an aftermarket part) right before the system is charged. Upon opening the sytem, the TXV was clean so I opted not to replace it this time.

In researching this latest A/C work, it seems it may be good practice to add oil to make up for what may have been removed due to the components that were replaced. Which leads me to a few questions.

Question 1) The car uses a Nippondenso 7SBU16C compressor. (BMW P/N 64526936883) What viscosity oil does this unit use? The best info I can find says PAG46.
Question 2) When replacing the evaporator and receiver/dryer, how much oil do you add to the system? There was no oily residue on the evaporator (both times) so it would seem the leak was primarily freon, and this second time, leak check dye.
Question 3) Reading here how PAG is hydroscopic, since the system was at ambient pressure for ~9 months, do I need to drain and flush the compressor and flush the condensor and lines?
Question 4) if I do drain the compressor, what volume of oil does the system require?

Since I do not have a refridgerant scale or a 30 lb cylinder, this time I was considering taking the vehicle to a qualified mechanic to perform the recharge, in hopes of getting the proper amount of refridgerant into the system. (1.63 +/- 0.05 Lbs) My previous method of looking at low and high side pressures was probably not very exact. Is there a good method by which to get a proper charge when using 12oz cans?

Thank you in advance for any help you are willing to provide.

Houston, TX

Edited: Wed July 14, 2010 at 12:52 PM by piperflyer

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