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1998 BMW 328i a/c compressor noisey & questions

nyc951 on Thu August 20, 2009 3:27 PM User is offline

Year: 1998
Make: BMW
Model: 328i
Engine Size: 2.8
Refrigerant Type: ?

Hi folks -

I'ts been a while since I've been here. You've already helped me fix 3 cars in the past, and now I need help on a fourth!

The a/c compressor on my 328i makes a rattling noise whenever the a/c is running. I don't think the a/c system was ever opened or worked on, so the noise could be oil that may have leaked out over the years.

For the short-term, do you think I should add a couple ounces of oil back into the system?

Can you provide the specs on this car's a/c system (oil and refridgerant capacity, pressures, etc). I haven't peeked under the hood, but I assume it's R-134a?

Thank you.

'98 328i

Karl Hofmann on Thu August 20, 2009 5:42 PM User is offlineView users profile

I'm not entirely sure that adding lubricant will help much... I would say that your compressor is on the way out, though it may be worth while to check that all the fans are running as they should because I have noticed that they gett more rattly as pressures increase..

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

nyc951 on Wed September 30, 2009 10:07 AM User is offline


Does someone have the correct low and high pressures for this car?

Also, if the car has R-134a from the factory, what oil can I use to add to the system? PAG 100?

I know this isn't the correct way to do it, but it'll buy me some time before I tear everything apart and do a proper flush/vacuum/charge.


'98 328i

HVargas on Wed September 30, 2009 12:05 PM User is offlineView users profile

If it is making noise it is likely on it's way out and just adding oil will not help the problem. If it was leaking oil it would be leaking refrigerant as well and you would have poor cooling. It is unlikely that even flushing everything out, vacuum and recharging with oil and new R134a will help the problem. You need to pinpoint the problem and fix whatever it is. Your system capacity of R134a is 34.4-36oz. It holds 3.4-4.8oz of PAG 46. Your operating pressure's should be from 164-215psi on the high side and 36-42psi on the low side with an ambient temp. of 80* and between 50-70% humidity.


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nyc951 on Tue July 03, 2012 7:33 PM User is offline


After getting the system evacuated, I finally replaced the compressor and drier, pulled a vacuum, drove the car to work, and checked the pressures again about 10 hours later. The vacuum had dropped to 28 in Hg by that time, but I wasn't sure if the slight loss was due to the air in the long hoses or not. I pulled another vacuum and then charged the system and was only able to get 2.5 cans (each 12 oz) of R-134a into the system. Here are the stats:

- auxiliary fan working properly
- ambient ~83 degrees
- about 60% relative humidity
- engine speed 2000 RPM
- High side ~ 250 Psi
- Low side ~30 Psi
- Vent temps with doors open and recirculation buttom OFF = 43 degrees

Should I try to charge the system a little more (use lots of hot water on the can) to get closer to the 34-36 oz of R-134 capacity? Will running the system in its current state of charge cause any issues?

Thank you all.

'98 328i

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