Yesterday, we decided to run into town in our '07 BMW 335i, which we had not driven since the “lockdown” in mid-March. It seems to be a bit PO’d about being ignored for so long.
First, when we parked, and sat in the car to eat lunch, the battery warning light came on, which indicates the battery is approaching end of life. Not unreasonable, we bought the car back in about '12, and haven’t touched the battery since. So, went to the parts store, bought a replacement for $160. Not too bad by today’s standards, and it is a big sumbitch. Like all modern BMWs, it mounts in the trunk. When I uncovered it, I was amazed at what I saw - there were about a half dozen cables plugged into or bolted bolted to this gigantic red plastic terminal block fastened to the top of the battery. It covered about 2/3 of the top of the battery. I un-did all that, remove the brace running over the battery, and the clamp holding it to the floor of the battery well. It took almost all I had to lift that big mother out, from a very awkward position. It was even harder getting the new one in. After about 30 minutes, the old battery was out, and the new one was in, a re-connected.
Next surprise? It is no longer enough to simply replace the battery. You have the TELL the computer you’ve replaced the battery, and the kind of battery you’ve put in! Apparently these cars some with either 80, 90, or 100 A-hr batteries, and they are either lead-acid, or AGM (Absorbent Glass Mat) construction. It appears the computer custom tailors the charging profile based on the type of battery, the capacity of the battery, and its age! I had no clue! Luckily, my BMW-specific OBD scanner was able to set the new battery type, and make the computer happy. And, the computer told me the old battery had been installed in '11, probably about a year before we bought the car. So, I just installed it’s third battery, at about 140K miles.
The next, bigger problem is the AC stopped working. No cold whatsoever. And, Holy Moley! Car AC systems have changed BIG-TIME! First thing I noticed when I saw the AC was not working was I heard no AC clutch “click” when I turned the AC on and off. Naturally, I assumed the problem must be a failed clutch, or clutch relay, or a rat chewed through another !@#$%^& wire. But, no such luck! Turns out, there is NO A/C clutch, no A/C clutch relay on this car! Instead, the compressor is a variable-displacement swash-plate type, with the displacement actively controlled by the climate control computer! The compressor is spinning ALL the time, and the displacement is reduced to zero, or near zero, when the system is up to pressure. Displacement, and flow rate, are modulated by the computer, based on load. I had no idea such a change had been made in AC systems, but this is apparently how virtually all car AC systems now function. And, of course, they no longer use R134a. There is a newer, more environmentally friendly refrigerant used - don’t recall what it is. This car just missed that change by about a year, so it is still 134a.
So, what’s the problem with mine? Beats the hell out of me! Fuses are fine, the system is properly charged, but it is developing NO pressure on the high side. The whole system just sits there at 30-35 PSI, on both high and low pressure sides, engine running or not, AC on or off. I’m hoping it’s something simple, like a failed pressure sensor, but I have no clue how to test that, since it’s a solid-state sensor, NOT just a simple pressure switch like on older systems. I fear that, for the first time since we bought this car, I may have to take it to an “expert” who has the equipment and knowledge to debug this problem properly.