pbsry

Howdy all,

My AC started blowing warm a few days ago, and I can't figure out the problem. Here's where I'm at so far:

Diagnostic Values:
1 116
2 143
3 114
4 112
5 111
6 199
7 12
8 127
Note that I'm in Alabama, and it's 90F+ ambient here. Car was warmed up from idle and was sitting in the bright noon sun when those numbers were taken.

Things I've checked/attempted so far:
0.) The compressor is spinning when AC is active, and stops spinning when I turn on EC. Aux fan is spinning. There doesn't appear to be any gradient of temperature across the driver-to-passenger side vents.
1.) The first time I checked the diagnostics, the #7 pressure was 24, which was higher than any valid number I'd seen, and the aux fan was turning furiously. I released some of the R134a from the low-side port to ensure the system wasn't overcharged. I probably released too much, because it dropped #7 down to 04, and the aux fan stopped spinning. I then recharged the system up to the 12 number you see above. After doing this, there is a pronounced hissing sound. I don't *think* it was there before, which makes me thing that maybe there should still be more freon added, but short of taking it to a shop for a proper by-weight fill, I'm not sure where to stop given our high ambient temperatures. The hissing sound does go away if I activate EC.
2.) I gave the duo valves a couple of good whacks to make sure they weren't sticking. I don't think the numbers point to that as a problem, but a whack is free...
3.) I pulled AC error codes, and found B1231 (ECT Sensor), and B1234 (Sun sensor). I reset those codes, and they haven't returned.
4.) I have not run a flap test yet, but don't think it should matter if everything is blowing hot anyways?

Short of taking it to a professional (any recommendations for Huntsville, AL?), anybody have any ideas?

pbsry

Crickets. That bodes poorly :-)

As a last ditch effort before I take it to a professional, should I add more R134a until the hissing goes away? I've always thought that the hissing was a universal "too low on freon" sign, but I'm not sure.

khomer2

Post all the values again, It first needs to be done with the engine cold and with the car out of the sun.
Then post the numbers when you start the car with a hot cabin.

Also, go thru the stickies here and read some more.

EDIT:
More specifically, read the ENTIRE post.
https://www.benzworld.org/threads/ac...d-air.1265436/

pbsry

Thanks for the reply, khomer2,

I've read through the stickies and that specific thread. The below is the reading from this morning (cold) and the prior
ID | Wed AM (75F) | Mon PM (90F+)
1 | 80 | 116
2 | 78 | 143
3 | 76 | 114
4 | 76 | 112
5 | 78 | 111
6 | 80 | 199
7 | 05 | 12
8 | 76 | 127

I'll note that this PM when I tested with the car warmed up, all the other readings were about the same except #7, which was a little lower at 10 (it was also a little cooler today at only 85F).

I'll note also that the low-side pressure reading (according to the gauge on the R134a dispenser was in the "high" range (~80psi), and after ~15 minutes of attempting to add more freon was only ~2oz seemed to have added based on decrease in can weight.

My guess upon a re-review of the stickies at the specific thread remains the same: that I'm low on Freon; alternatively, the pressure difference across the compressor is poor (high side too low, low side too high), which could indicate compressor failure?

Any guidance is appreciated.

khomer2

I doubt it's failing - no code like b1419 - this would be a clutch issue (ie. failing compressor)
I believe you bleeding out r134a (not knowing how much bled) and then recharging has got your AC in a bit of a mess.
A good ac setup should read in the range of 40/200 psi on proper manifold gauges (you're measuring off a can gauge - not the best imo)

Go thru this link - it's good info to assist your step-by-step (and more user friendly)
Follow the guides to getting the correct readings thru the MB diagnostics
http://www.mercedesmedic.com/ac-air-...le-codes-list/

Also, read this to get a better understanding of the pressure readings.
https://aircondition.com/tech/questi...ith-gauges-faq

Looking at your readings, you're still low on your 134a.
Also, observe your pressure fluctuations in a hot car when AC should run at full tilt.

EDIT:
Here's a bookmark I have for AC troubleshoot. This should be helpful.

https://mbworld.org/forums/e-class-w...questions.html

Plutoe

For your issue the important data point is 7 refrig pressure and it should be 15 to 17bar at idle, if not you lack refrig or your compressor cant make pressure, forget the HS if you had a compressor fault your EC light would be on and you would not be able to turn it off----is yours on or off???

pbsry

Hi Plutoe,

My EC light is off, and my clutch is engaging and spinning. Agreed that #7 is low, and given the lack of any fault code for the compressor, my best guess is that it's low on freon. What's killing me here is that I've tried adding freon, but it's like the system won't accept any. (~2oz after 15 minutes). If the thing would just throw a fault code...

pbsry

Sanity check: If the clutch is spinning, the compressor is engaged, right? I.e., I can turn on EC mode to test and see the clutch disengage...there isn't a second clutch somewhere or something, right?

khomer2

correct.
That's the only clutch on the compressor for ac.

pbsry

So I finally got a manifold gauge set from my friendly local auto parts store:
0.) Afternoon, cold engine, 80F ambient
1.) Static pressure with the engine off was about 7 bar on both sides
2.) Running pressure was...the same on high side and low side: 7 bar. This matched the Sensor #7 readout as well. AC clutch was engaged and spinning.

If I'm making absolutely no difference in pressure whether the compressor clutch is engaged or not, the obvious explanation to me would be a compressor failure...Before I dive in to perform the swap, is there any other alternative I should consider?

Plutoe

Yea, don't do the job yourself. Have it done correctly and or remember you have a 2000 dollar car

pbsry

Having it done correctly seems incompatible with a $2K car, but I don't disagree :-D I'll take it to a proper shop and report back once I'm up and running.

pbsry

Got my car back today from an awesome independent mechanic (PM me if you are in my area and want a referral), and here's what he found:
1.) AC compressor shaft was broken.
2.) Receiver dryer/accumulator was completely blocked up
3.) Slave auxiliary fan had slipped its belt
4.) Small amount of AL dust in the oil was flushed out of the system (he wasn't surprised given the age of the car and the issues seen)
5.) System was holding pressure

His working theory was that the receiver dryer/accumulator blocked completely, causing pressures to go sky-high (Remember that #7 sensor at 24 bar that kicked this whole thing off?), and shortly thereafter killed the compressor. The slave auxiliary fan having slipped its belt didn't help the situation, causing pressures to go even higher.

On the negative side of having the V8, apparently the engine must be loosened from the mounts and raised a few inches to provide proper clearance to remove the compressor...not great for the labor charges. All told, compressor replacement, receiver dryer/accumulator replacement, expansion valve replacement (cause why not...already in there), replacement of the aux-fan belt, flush, fill, and labor came to ~$1500. More than I had hoped, and a bit high on the parts prices in the itemized, but for the first time I've taken a car to a mechanic in my life, I'm satisfied. I intend to own this car for many years, and with near perfect condition and less than 100K miles, I should be able to pull that off.

Hope the thread helps someone.