I'm having problems with the AC system in a 1996 S420 (W140).
Basically, the car has a history of AC leaking, but nothing too drastic -- a pound or less of r134a brought it back to form and the pressure switch never had to turn off the compressor. A couple weeks ago, however, after recharging the AC system something went for the worse. My mother had been driving the car and she mentioned that on the way to her destination, she turned up the fan to the highest setting with the AC on. Briefly thereafter, the fan "clicked off" along with the AC, and refused to turn back on. Upon starting the car for the return trip home, she tried the climate control system again, and the fan came back to life, but the AC was still amiss. This was about as much technical detail and observation as I could get from her.
Right now, the "EC" button is lit and pressing it again will not make it go out. This button is supposed to disengage the compressor, and indeed, the compressor refuses to spin no matter the temp outside, inside the cabin, or climate control temp setting. No compressor makes recharging futile, too. However, I was able to rig the fog-light circuit from the fuse box (both rated with 7.5A fuses) to feed power directly to the single contact on the compressor and the compressor spun up normally. I tried to recharge the system this way, but pressure readings from the low-pressure service port suggested normal refrigerant pressure. I thought maybe the pressure switch on the accumulator was bad so I tried shorting the connector. There are three contacts on the connector and I tried shorting them in all combinations. Nothing in the system responded, as far as I could tell. This leaves a possible temperature switch in the evaporator, which I assume I have to tear off the dash to get to, so I'll wait on that one. Also, there is a two-wire connector going to the accumulator which I had left alone, thinking it was also a temperature switch, is that right? Directly before the low-pressure service port, and right next to it, is a pill-container sized cylinder with a line from the engine and a line towards the lower back of the engine compartment -- are these vacuum lines connected to a throttle cut-off switch? And is there anything else I can look at without the DTC's?
Which brings me to the last part of the question -- would standing DTC's keep the climate control from turning on the compressor? Do they have to be cleared in order for the EC button to toggle off?
First- stop jumping wires. The system shut down in the first place(w/mom) because it was probably overcharged. With no sight glass you have NO way of knowing how low the system was. Your next step would be to have the system evacuated, and the proper amount installed. Have some oil installed when this is done. Being you have a slow leak, you not only loose 134, you loose oil also. Sooner or later your compressor will take a vacation. Wise to add some dye also to find your leak. It could be something stupid and cheap. You must pull the codes and clear them after the above procedure for the system to function again. Remember - don't overfill. Everything having to do with the HVAC is monitored and stored. Good luck, Kevin
Alas, you are right that shorting to the compressor was a big risk, but I had to be sure of the compressor before moving onto other diagnostics. Fortunately, I use PAG oil on every recharge and the last recharge also included some dye. However, it was only a couple weeks ago and I didn't observe any dye, so I think maybe it might just take a bit longer to leak enough to see it.
Now that I think of it, both the PAG and the dye include some refrigerant to pressurize their respective cans, so I indeed could have overcharged. Also, I usually try to charge to 35 psi, but without a good conversion from the 2.5# listed on the sticker to actual pressure, it's hard to tell. Hmm... perhaps I should just get it done at a shop and then make a note of the pressure properly filled...
As for the codes -- do the standard OBDII tools for the MB cover Climate Control, or do I need to get access to one of the professional $2k+ units? I noticed only 16 of the 38 pins in the diagnostics port have contacts. Can finding out the right pins and connecting to a scanner do the trick?
I know I'm kinda of a "hacker" at this -- bear with me, please. I'll get it right eventually with sound wisdom from more experienced people as yourself.
Took a couple tries to get both the "actual" and "error codes" screens to come up on the ACC digital display, as I kept getting the actual displays the first couple times around. Then, I'd get a blank screen every now and then that would confuse me and I'd start over -- took a little more research to figure out that the blank screen is just the entry point into the error codes.
Other interesting points (that might be particular to this model and year) for the interest of others who may thread this path:
1. Car engine doesn't have to be running to get these screens, but depending on the readings you want, actual displays will be more interesting and relevant if it were. (ie. engine rpm)
2. Just holding "REST" for 5+ seconds with no other buttons pressed brings the actuals to display, temp and fan adjustments seem irrelevant. Units in my US car are in F for temp, psi for pressure, and mph. Volts and amps are same. And refrigerant pressure is for the high line.
3. Don't be discouraged by the blank screen when trying to get the diagnotics to show error codes -- the blank screen is to confirm that you're there. Just hit the right "Auto" to start the error code displays. Might take a second or two and the fan blows a puff before the first error code displays.
4. "FF" is the end of the error codes. Press right "Auto" again to recycle through the codes. If you have no error codes, this may also display as the only code.
5. I couldn't erase one code at a time, but holding down both left and right "Auto" buttons for a bit brings up a "d" on the left side of the display, and if you then hit the right "Auto" button to continue, it seems to clear ALL error codes.
6. This website, which also discribes the process, has charts that will help you interpret some of the codes: http://www.continentalimports.com/ser_ic40142.html
Anyhow, after addressing the problems (proper refrigerant fill) and clearing codes, compressor spins up again and AC is back on-line! Of course as a disclaimer, I would state that any errors could suggest actual problems that need to be addressed -- eliminating error codes doesn't necessarily fix those problems.
Does this procedure work for older w140 models? I have a '95 S320 with two small displays for the dual zone readouts as pictured below (I'm going to try to attach a jpg). I tried the procedure to bring up the fault codes but couldn't get anywhere. I'm thinking it is not available for my year.
For your ACC unit, the following link may be more appropriate: http://pages.prodigy.net/jforgione/MB_AAC.html
Try it and let us know!
BTW, I think my speed reading of the actual displays is actually kmh, not mph. And I'm guessing refrigerant pressure is in bar instead of psi, but "50" is 5.0 bar. Either that or my pressure sensor is whack. But AC runs normally, so far...
Excellent website! I can't wait to try this out. My Dad is having some problems with his A/C where it isn't ever blowing cold, and the fans seems to turn on and off at random times (or so this is how he described it). I am the one who convinced him to buy this car, so I really REALLY hope that it isn't a very big problem. I hope it just needs a recharge . . .
With the earlier W140s, does anyone know if deleting the fault codes is a safe thing to do? If there is a serious error that hould be corrected, will the system display the error once again in the future?
Linear Mode
