AC diagnostic - PeachParts Mercedes-Benz Forum

congonatty · #1 03-04-2004, 07:23 PM

W124, 1989 300e, What does swirling bubbles in dryer sight glass indicates. A/C compressor blows cold for 1/2 hour then clutch quits and ac blows warm. Where is the evaporator temperature sensor located, any illustration on how to access.

#2 03-04-2004, 07:51 PM

I cant remember where the ets is on that car, too long ago , tbut i think its on the right side of the heater case, by battery area. look for wiring going into the case or maybe its in the case under the cowling, anyway dont worry too much about a small amount of bubbles in the dryer its fairly normal but does indicate a possible leak.If I remember right , you probably have a problem with your compressors speed sensor(located on the back of the compressor. the signal should be greater than 3.5 volts a/c, if the signal goes open your compressor will disengague. this can be cked at the klima relay, you will need a wiring diagram to find the proper pin locations, you will need to bridge the compressor and measure the signal at the same time. be careful if you dont know what you are doing you can hurt yourself. you might want to see a professional technician.good luck.

whunter · #3 03-04-2004, 07:53 PM

what is your ambient temp in SC today?
Swirling bubbles in dryer sight glass indicates nothing below 70F.

leathermang · #4 03-04-2004, 08:56 PM

I do not know about YOUR car model...
But in case it is constructed like a 123 then you have a block thermosyphoning valve/........
Which is a combo unit at the beginning and end of the evaporator core... tied together as sensor and controller....
Your temp sensor and pressure sensor are at the top of the Recieve/Dryer...
And some systems have a ' superheat' sensor in the compressor... but probably not yours...
Looking at the bubbles by themselves without other factors ( like WHunter mentioned ) is really not very useful... too complicated and too many variables at this point in time...
Are you running R12 or R134a or something else ?

congonatty · #5 03-05-2004, 04:01 PM

89 300e,Temperature was 78 yesterday in NC & car is using R12.
Trying to get some input as to what could be causing AC to cut in and out. Will run for about 1/2 hour blowing ice cold then blow warm and resume cold air blowing after 1/2 hour or so. Klima relay replaced, fuses ok, belt tight, unit fully charged, no leaks, temperature sensor in headliner overhead light replaced, been to 2 AC shops, 1 Indie bosch authorized and 1 non indie AC only repair shop and both shops could not determine cause of intermittent operation. The AC non indie repair said it must be one of the numerous sensors in these MB climate control system and the indie shop said the clutch disengages when hot but could not found what causes it to disengages. Trying to get information on the climate control sensors location so I can do a DIY replacement. After being to two separate shops I have decided to either live with it or try and troubleshoot and repair myself. Also talked with several indie shop that also repairs AC and they also seems puzzled, said they would have to do a diagnostic.

adiel · #6 03-05-2004, 04:34 PM

congonatty, check out this article:

http://www.mercedesclub.org/_disc2/000000b1.htm

Adiel

congonatty · #7 03-05-2004, 04:44 PM

Thanks, already seen that or similar article and have changed out the monovalve also with no change in ac operation.

leathermang · #8 03-05-2004, 05:45 PM

Wow, you have replaced a lot of things.... so I will have to ask some questions which may sound like I don't believe what you have said... but this is the only way I know to ferret out what may be wrong....
When you say ' fully charged' EXACTLY how was that determined ? Expound as much as you can on that process.

congonatty · #9 03-05-2004, 05:56 PM

System was fully charged with R12 at ac shop and rechecked after system began acting up. I personally changed out the temp sensor at the overhead light/headliner, the monovalve and the klima relay with no change in system operation. Shop also tried new klima relay which was later removed because that was not the problem.

leathermang · #10 03-05-2004, 06:05 PM

What do you mean by fully charged ? How was that determined?

whunter · #11 03-05-2004, 06:15 PM

Hello congonatty
Suggestions:
#1. Ambient external temp sensor. false signal.
#2. Engine temp sensor for computer. false signal.
#3. Clutch coil defect, coil overheat circuit broken.
#4. Radiator plugged with scale, engine temp (computer) sensor shutting down compressor.
#5. Evaporator core freeze up.

leathermang · #12 03-05-2004, 06:18 PM

I think the system is overcharged.

congonatty · #13 03-05-2004, 06:18 PM

Do not know the full procedures but as stated before I took it to indie repair shop where vehicle was r12 charged and dye placed in, when system began acting up, vehicle returned and was checked by mechanic, they stated no leaks and system does not need additional freon.

leathermang · #14 03-05-2004, 06:20 PM

I am saying it may need less freon.....

leathermang · #15 03-05-2004, 06:24 PM

" but as stated before I took it to indie repair shop where vehicle was r12 charged and dye placed in, when system began acting up, vehicle returned and was checked by mechanic, they stated no leaks and system does not need additional freon."

Yes, I read that... and you did not say GOD checked it.. and you are having problems which this " mechanic" did not find... if you are not willing to get ' down and dirty into the details' then how do you expect us.. ,who can not even put our hands on the car , help you ?