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First problem ever with my E550. Today I changed the Auxiliary battery under the dash because I got the Aux Battery Malfunction warning. Started the car, no warning, drove a few miles, then it seemed the AC stopped working mid drive. Coincidence? I don't know. Now it does not blow cold at all.
I borrowed a set of gauges from Autozone to check the pressures. Low side is about 140 (extremely high) and high side is just over 150. This is with the car running and AC on MAX COOL. I have read that pressure may read like this because either 1) the compressor is not turning on, or 2) the compressor is running, but not actually working.
I don't notice any change in sounds from the engine area when I click the AC system to off and back on. I looked at the compressor pulley and it looks like it's always spinning, center and all, whether AC is on or off. Most cars, when the system is off, or the clutch is not engaging (compressor not running) the center section does not spin, only the outer pulley. Is this true of my W212? Anyone with AC tech knowledge here? I'll take it to a good indy shop on Monday that deals with AC, but looking for any hints to try over the weekend. Is the compressor actually running or not? Possible electrical issue? Are there any built-in AC system diagnostics like the older Benz?
I would check some fuses. I can't see how changing the AUX battery could cause any problems on a 2012, unless it tripped a fuse. Easy enough to check.
Yes, maybe total coincidence. As I said, it worked just after the battery swap, then seemed to quit blowing cold mid trip. I looked all over, but I don't see any fuse listing related to AC compressor, HVAC, or AC system really. I see one listed as "AC System Heater (12,66)"
This compressor does not have the conventional clutch that clicks ON and OFF that you can hear. Compressor by my understanding is a variable piston stroke compressor that controls compressing internally.
By the pressure readings your compressor is barely doing anything. High and low side pressures being almost identical means compressor is not doing it’s job so the first thing to do is to check all fuses that are A/C related like was already suggested by DFWdude.
This compressor does not have the conventional clutch that clicks ON and OFF that you can hear. Compressor by my understanding is a variable piston stroke compressor that controls compressing internally.
By the pressure readings your compressor is barely doing anything. High and low side pressures being almost identical means compressor is not doing it’s job so the first thing to do is to check all fuses that are A/C related like was already suggested by DFWdude.
Forgot to mention that a faulty system pressure transmitter would not allow the compressor to function so a scanner that can read the pressure would be a big help.
Checked fuse 12, ok, 66 does not have anything in my car. Taking it to a specialist on Tuesday hopefully. In the mean time, this sped up my wife's decision process and picked up a CPO GL550 with 39k miles today.
Did you search the forum?
I think I posted troubleshooting procedure at least 100 times here and maybe 1000 times on other forums.
Anyway, with 7 or more sensors operating the system you can't crystal ball the problem.
Start troubleshooting reading codes and then with calibration test on cold morning before engine start. All temp sensor should be within 3F from each other.
Post results here and I can help with interpretation.
140 psi static pressure sounds high, but not knowing temperature it is wild guess.
No need to risk the system by hooking up outside gauges. The car high pressure sensor will troubleshoot it just fine.
Diagnosis is bad compressor. $1200 for OE equivalent replacement. Still cheaper than any extended warranty and I've had the car for 5 years, I'm not really mad about it. My wife's Nissan compressor died at 70K. Florida heat is a *****.
09-04-2020, 11:34 PM
