[mictang]

Hey guys,

So I had some work done on my N52 E90, which required disconnecting the AC lines three times in the past year. Each time was a couple of months apart, and the lines were reconnected roughly within 24 hours (overnight) and recharged every time.

On the two previous occasions, AC worked fine. However, the most recent time I started noticing reduced AC performance. Sometimes, it would not blow cold enough at a standstill, but it would go back to normal after some time or when the car was moving again.

ISTA showed 11 bars and 8C evaporator temp at idle, ambient was around 26C.

I have moved so I can't bring the car back to the original shop that did all the previous work. One of the reputable shops in my new region suggested it could be the compressor starting to fail given the above mentioned readings.

I had first suspected an incorrect refrigerant charge amount at first, but the new shop said the pressure reading is within range from their experience (I know this isn't a definitive confirmation of correct refrigerant weight in system).

After some more reading in ISTA, I found two additional probable issues: PAG oil loss and condenser drier degradation.

For the oil, I wonder if some oil was lost each time the lines were disconnected and it finally started to cause an issue. (I know this could mean compressor damage)

Also, ISTA states the drier in the condenser should be replaced if the system is left open for more than 24 hours, mine was open for over 24 hours cumulatively but probably not on any single occasion, I do have an early production date so I can just replace the drier rather than entire condenser.

So here are the options I am trying to decide to try:
1. Pull vacuum and recharge again, and add oil (not sure how much to add though).
2. In addition to oil and recharge, replace the drier element as well.
3. New compressor plus all of the above.

I don't mind replacing the compressor if I can be a little more sure that it is actually going bad; my other 2012 F chassis N52 car also had a compressor replaced last year, so my 2007 E90 had lasted this long isn't bad. The compressor does look like an OEM Denso unit, but I can't tell if it's original to the car, I have had the car for the past 7 years)

As for the oil amount, ISTA states a top up amount of 20mL for excessive refrigerant losses, 50mL (including the oil pre-filled in the compressor) for compressor replacement, and 35-55mL for other major parts replaced due to leak. I am thinking maybe 60mL (20mL * 3) for my case. I couldn't find any official source on total oil capacity but the forum mentioned ~6fl oz a few times (~ 170mL) which I feel could be an excessive amount to add.

Recharge cost is quite cheap locally so I am leaning toward option 1 and if things doesn't improve, I would simply go all in and replace the compressor.

Any thoughts? Comments and suggestions would be highly appreciated!

[lobotomy]

I would go with evac & recharge also. Very important to draw system down to a vacuum before adding proper refrigerant. The drier may have moisture accumulation, so deep vacuum to remove moisture is a must! As far as oil, it depends on where lines disconnected. Lines taken apart high up may not a big deal on loss. If a component like the condenser was removed, then I would consider adding a bit.

[mictang]

Well, I had the AC system pulled to a deep vacuum and recharged 600g of refrigerant (my pre-LCI calls for 590 +- 10g).

There was a decent amount of oil that came out along with the refrigerant, so I only topped off what came out.

The behavior is generally unchanged; idle evaporator temp is around the same and I still get the occasional "cutting out" in AC - pressure drops and evaporator temp rises to around ambient for maybe half a minute and then goes back to normal.

There are 0 codes, could this be evidence of the compressor going bad?

[ptpending]

probably compressor going bad
the AC system should be serviced in the beginning of every hot period after 3-5 years of the manufacturing
all bmw petrol 1 series and 3 series have a design issue that freon line lies on front right rail and nearby are exhaust pipes which are very hot
so constant contrast heating and cooling affect the aluminium and pipe become weak
also all metal-rubber joints become less germetically after 5-7 years
that lead to freon and freon oil starvation for the AC compressor, even if it still work
and that lead to premature AC compressor failure
bmw diesel cars exhaust pipe are not so hot and diesel cars have less AC compressor issues
to prevent this problem you need to check amount of the freon and oil every year after 5-7 years of car life, to get the first signs that car lost some amount of the gas and oil

[mictang]

Originally Posted by ptpending

probably compressor going bad
the AC system should be serviced in the beginning of every hot period after 3-5 years of the manufacturing
all bmw petrol 1 series and 3 series have a design issue that freon line lies on front right rail and nearby are exhaust pipes which are very hot
so constant contrast heating and cooling affect the aluminium and pipe become weak
also all metal-rubber joints become less germetically after 5-7 years
that lead to freon and freon oil starvation for the AC compressor, even if it still work
and that lead to premature AC compressor failure
bmw diesel cars exhaust pipe are not so hot and diesel cars have less AC compressor issues
to prevent this problem you need to check amount of the freon and oil every year after 5-7 years of car life, to get the first signs that car lost some amount of the gas and oil

It sounds like you are saying exhaust heat causes leaks, which in turn ruins compressors. Or is it that compressors are also getting a reduced service life due to heat at the same time?

My other N52 F series lost AC completely when the compressor went bad, it had no leaks, and new compressor fixed the problem. So I always thought these cars had a relatively weak compressor (which could be caused by the exhaust heat like you mentioned).

[ptpending]

Originally Posted by mictang

It sounds like you are saying exhaust heat causes leaks, which in turn ruins compressors. Or is it that compressors are also getting a reduced service life due to heat at the same time?

My other N52 F series lost AC completely when the compressor went bad, it had no leaks, and new compressor fixed the problem. So I always thought these cars had a relatively weak compressor (which could be caused by the exhaust heat like you mentioned).

the compressors for N52 F series have different partnumber than N52 3-er and 1-er have

[mictang]

Originally Posted by ptpending

the compressors for N52 F series have different partnumber than N52 3-er and 1-er have

Yes, but likely just due to different accessory belts. I looked at them in person and they are pretty much the same thing physically and electronically, also both made by Denso.

[ptpending]

I do know that BMW never build different part if it can reuse existing.
So if you mean that they are same but have different part number, then thats looks like nonsense
also i've looked up a engine picture of the N52 from F series and it has AC compressor at the same place.