Quick A/C question

[02Pilot]

The A/C on my 128i is not keeping up with the heat wave we're currently experiencing - barely cooling even cruising at highway speeds. Low side is reading ~30psi with ~90degF ambient (probably more like 100degF with the heat reflecting off the pavement). This is, according to what I'm reading, too low; should be ~50psi at that ambient temperature for an R-134a system.

I know full well that the proper procedure is evacuate and refill by weight, but I will not be able to get to my indy for a couple weeks, and that's not going to fly (black car, dark interior). I've got some straight DuPont R-134a (no stop-leak). Questions are simple: 1) Anything unusual about the A/C system in these cars that I should know?, and 2) Are my numbers correct (I checked multiple sources, but nothing BMW-specific; I'm assuming the pressures are standardized for R-134a systems, but confirmation would be nice)?

[02Pilot]

OK, I went ahead - if it all goes horribly wrong, I blame heat exhaustion.

Put in the better part (~2/3rds) of a 340g can of R-134a. That got the low side up to a maximum of ~45psi, the bottom of the range for today's ambient. I took a short highway drive and checked again when I got back: ~35psi. Came back up to ~45psi after idling for a few minutes (all this done with the A/C on MAX, BTW). I'm tempted to add the rest of the can, but I don't want to overfill accidentally.

I'm not saying it's perfect, but it's now blowing cold. It still feels a bit less productive than I would like, but considering the color of the car and the heat (surface temps ~120degF in the sun, ambient ~93degF) I'll take what I can get.

Feel free to tell me I'm a hack. At least I'm no longer melting.

[MauiM3Mania]

I may be a hack as well, but I'm a comfortable hack!

My E46 M3 apparently has developed a leak in the a/c system which requires the removal of the dash to correct. It took 20 months for the system to empty to the point the compressor would no longer engage. My choices were a multiple thou$and dollar repair or refill it myself.

I spent $160 on the set up to evacuate and refill and $24 in R-134a as it took two ounces beyond two cans. Next time, it will be about $16-24 for the freon.

[MIKYZZ4]

No worries 02Pilot, I'm a hack when the only other choice is - Sweltering!

I believe the max refrigerant capacity is 1.2~1.5lbs. for BMW systems,
so you basically added 1/2lb to a possibly low system, so you should be fine,
considering the pressure max you sought to achieve.

[02Pilot]

The system is supposed to be 590g max fill, so if I guessed correctly and added 2/3rds of 340g (~225g), I added a little less than half of the total. Given the low initial low-side pressure, I'm thinking it was pretty depleted. The PO didn't seem to use it much, and I have no record of it ever being serviced, so I wouldn't be at all surprised if it just slowly leaked down over the last nine years.

[bmwdirtracer]

While I understand that the tables show up to 50 psi on the low side, at high ambient temps, modern a/c units don't generally produce that, unless the expansion valve is bad. In fact, the very coldest vent temps are always produced when the low side is at ~30 psi or so, up to 35 when it's really hot....

I finished replacing the compressor, dryer and expansion valve on a 2009 Jetta today, filled it with the correct weight of R134a. Low side, at ~85 ambient, showed 25 psi. High side was 160....vent temps were 38 degrees!

Certainly, I empathize with everyone wanting to stay cool. I brought in a Volvo today, from the hot sun, to do work on the interior. I left it running, a/c on....

[02Pilot]

Interesting, Chris. It was seriously stupid hot here today, but I take your point. I did not get the vents to produce truly cold air until I had pumped in at least half the can (so ~170g, or a little less than a third of capacity) and saw the pressure come up to ~45psi. As I said, after a drive that blew some less hot air through the condensor it registered ~35psi. Not sure if I ended up overfilling a bit, but it's definitely blowing cold air now, which is what I was after. I need to get a thermometer in the vent to see just how cold.

[MIKYZZ4]

Thank for that informative confirmation Chris,
could very well prevent disaster on my next hack, lol.

[nelsonjmbf]

i have a 2004 525i with around 120k miles on the engine, the ac works good once i start moving but im wondering if anyone has had this issue before, when i first start the car for the day or after its been off for a few hours the ac will only blow semi cold almost warm air, no matter how long i let it idle for the air will only get so cold but as soon as i put the car into gear, whether drive or reverse and move a foot or two the air will instantly get cold an stay cold. The other issue i have noticed is that it will turn on by itself when i am in park, it has never done it while driving only while in park, also sometimes i can feel that it is tsaking power away from my foot when i run the ac and am trying to accelerate but i think thats kind of normal in a fourteen year old car.

[bmwdirtracer]

Nelson, it's likely that your electric auxiliary fan isn't working, which could cause your engine to overheat, when you get in stop-and-go traffic. If that engine overheats, you'll likely need a new engine. If the temp gauge moves beyond the normal 1/2, you are in imminent danger of overheating.

The a/c compressor can consume ~10 horsepower, but it shuts off under full throttle.

I'd suggest that you visit a BMW specialist shop, and let them diagnose your a/c system and cooling fan, before you need a new engine.

[nelsonjmbf]

my fan comes on fine, an i never have less than two bars on the temp gauge behind the tach, i havnt recorded the digital temp but i will take a drive a see how warm its getting, is there ant way to tell if the fan isnt working? i have an k+dcan cable and am currently trying to download bmw standard tools

[bmwdirtracer]

The first step in diagnosing an a/c system is to evacuate, vacuum, and refill with exactly the correct amount of refrigerant.

[nelsonjmbf]

would you happen to know a good link to a diy for that? Sorry i am still learning lol thanks very much tho.

[bmwdirtracer]

It's not a DIY. This requires a professional a/c service machine.