Pbc Codes - PeachParts Mercedes-Benz Forum

doug richmond · #1 12-30-2003, 02:29 PM

Greetings everyone. I am desperate to find the Climate control codes for a 1995 S-320. Codes for other cars arent adequate. Im trying to get the code to diagnose the pbc itself. The climate control was intermittent but is now inop.
The PBC codes show the freon press to be slightly low (i think) and thought this might be the culprit. I installed a new fan/reg from fastlane first, no help. Then found out how to retrieve codes from the pbc but I cant find the "magic decoder ring" to decipher what the pbc is showing. I brought it to a MB independant tech, what a joke!!! He tried to charge me $85 per hr. and could find nothing while telling me how complex a job it was but when I asked him what the pbc codes showed, he said "you can do that?" :-o Im ready to make lemonaid out of this frickin car!!
Thanks in advance for any link or info. Doug: eek:

Gilly · #2 12-30-2003, 04:36 PM

Can you explain it better detail what is wrong with the climate control?

Gilly

doug richmond · #3 12-31-2003, 01:16 AM

Not much to describe. It is inop. Lights show on each button but no response to any command except to test and go through sequence of codes. I removed pbc, opened, found all solder connections normal and no obvious defects. The car seems to have defaulted to max hot air from all dash vents and defrost. I can control nothing. When not in EC mode the a/c compressor works and forms frost on supply line, indicating it works, but with no fan and or vent control everything stills flows max hot. The system problem started as intermittent and has now gone full time over a two month span. It looks like I may have to cave and grovel at the MB dealer. Im tempted to throw a pbc at it but Im not convinced. What do you think? Doug

stevebfl · #4 12-31-2003, 08:31 AM

It sounds to me that you have a blower problem. I wouldn't worry much about fault codes they always seem to accumulate, but I very seldom get any usefull info from AC fault codes.

There is much writen about diagnosing the blower control on a 140 car and it is actually very simple. Remove the large cover at the right to center of the area below the windshield (numerous large phillips screws). Dislodge the routing of some hoses at the middle and leave the vacuum lines attached. Fold the cover to the side. This is the way into the fresh air filter and is purposely easy. Below the filter is the blower and the circuitry. There is a black chunk about an inch square mounted on the blower (comes with new blower) that is the blower regulator. It regulates by varying the current flow on the ground side of the circuit. So there are two large current carrying wires attached. There is also a signal wire attached that carries a 1-6v signal telling the regulator what to do. Look at the circuit find the ground wire from the blower. Check the power to the blower and then jump the ground from the blower to ground bypassing the reg. If the motor works, you have a regulator or control circuit problem.

If the testing is done properly a current test should be done as a high current motor will take out the regulator in short order. This is especially important on the 140 as the regulator comes with the motor.

You might also refine you capability to find a MB technician. You are right, he is not a MB technician if he doesn't know how to manipulate the PBC. Personally, I wouldn't use fault codes to look at your problem, but I would use actual values. One of the actual values is the PBC's idea of what control voltage was sent to the blower regulator. That should be the same as what is found at the regulator and it should rise and fall as the blower wheel is turned from "min" to "max".

And if you decide that the control signal is bad due to the PBC go here: www.beckmanntechnologies.com

Gilly · #5 12-31-2003, 10:21 AM

I don't buy in to the diagnosis of the blower motor control being the root cause because the climate control, as Doug explains, has gone to full heat, no temp control either.
It's possible that one of the fuses is providing no power to the climate control. It may have other power sources which are providing power to run through the test progrm and allow the LED's to switch, but missing another power source to actually control the temp and fan.
With the key ON or car running, check some of the fuses for power using a meter or test light. Check the fuse chart for ones which refer to the climate control system.
I had a 140 acting similar to this (at least in regards to the blower motor, unsure about temp control) which ended up having a bad ignition switch of all things-not even providing power to one of the fuses which the climate control uses.

Gilly

JimF · #6 12-31-2003, 11:31 AM

that the PBC is bad, send it to Beckmann Technologies via the link at the bottom of my web page (click the "WWW" icon below).

They can fully test the unit and repair, if bad, for a reasonable price.

doug richmond · #7 12-31-2003, 02:45 PM

Thanks, Steve, Gilly and Jim. Ive been through all of the normal shooting stuff, fuses, key switch, voltage to fan, jump fan to blo works fine but still no control of air. One thing that stands out is the two little lights on the dash above the pbc on the center vents dont work (red&blue). When the system used to spring to life on occasion all controls and lights would function normal. When it went belly up only those two lights wouldnt work. Anyway, Im thinking temp sence or something along those lines, vacume pump doesnt seem to be over running, door autoclose works along with everything else in the car . Have you guys ever seen slight low freon act like this? Its supposed to be something like 11 bar or some such and is showing 9.5 to 9. Thats on the pbc self test, would that be signifcant enough to make a diff? Anyway Ill screw w/ it somore. Sending the pbc to that place you guys suggested may be in order, atleast I can eliminate that cause. Also when I replaced the fan reg about a year ago everything worked fine (simular symptoms) now when I just installed another new reg, nothing changes. I may have a fan thats drawing loads of current and burning regs, but I think it should have worked for atleast a few min. Fan runs fine when jumped, prob not a good thing to do to fan ????? any Ideas

JimF · #8 12-31-2003, 05:05 PM

The PBC if ok, should not stop the normal operation of the a/c system unless the R134 is so low that the compressor gets locked out. But it has to be very low for that to happen; if you down even 1 lb (in a 2.5 lb system), it will still work.

I had what I was sure was a bad PBC! But it turned out to be a siezed compressor. The clue was reading the DTCs in the BASE MODULE (my page, MENU#8); sure enough there was a "DTC 7; belt slipping" code stored!

Anyway, good hunting!

doug richmond · #9 12-31-2003, 06:04 PM

Jim, thanks for the imput.
I checked belt tension and a/c compressor function normal, Im kinda thinkin pbc still but I think Im going to send it off to be tested or rebuilt. By the way, the famous "RADIO TOOL" thats required before you can own a MB is a crock of b.s. The perfect tool is the small blade of the standard Swiss army knife, works every time to remove radio and center console! This car makes me laugh, wouldnt you think a $70,000 + car would have an even half way reliable climate sys.