A/C Problems

3325 Views 17 Replies 4 Participants Last post by STARLINER W140, Jun 22, 2013

JJRAGE

Discussion Starter · Sep 30, 2011

Im rapidly loosing my mind over this..
I buy an S420, ac works intermittantly. Compressor kicks on, then off.

About a week later, compressor only comes on when i start the car for about 4 seconds then kicks off and never comes back on.

It appears the control unit has been replaced with one out of another car cause i get an E013 error, but theres no controls at the back seat vents.

Unless i unplug a sensor, no other E0 or E1 codes. Wierd. Whats REAL strange are the readings i get from the sensors. For example.

1-89
2-4
3-96
4-94
5-98
6-7
7-8
8-60
9-65

Seems ok, compared to the next test i ran.

1-17 (and was dropping, on a 90 degree day)
2-93
3-9
4-8
5-12
6-95
7-8
8-45
9-65

I feel insanity baring its ugly teeth against my skull lol. any ideas on what's fried on this 420?

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1 - 18 of 18 Posts

JJRAGE

Discussion Starter · #2 · Sep 30, 2011

heh, it took 1 can of 134a, no change. With the AC compressor not coming on, what should the refrigerant pressure be? I'm reading 8 bar

MikeJT

· #3 · Sep 30, 2011

Since sensor values > 99 loose their most significant digit in the 2-digit display, switching to degC gives values which are much easier to interpret. So I suggest that you repost some values with degC selected.

If your a/c clutch is pulling in for a short while and then dropping out, it's probably because the base unit is detecting a rotational speed error on the compressor. This can be caused by oil on the clutch plates, amongst other things. As far as your system pressure goes, 8 bar looks good at the sort of ambient temperatures you seem to have.

Mike

JJRAGE

Discussion Starter · #4 · Sep 30, 2011

MikeJT said:
Since sensor values > 99 loose their most significant digit in the 2-digit display, switching to degC gives values which are much easier to interpret. So I suggest that you repost some values with degC selected.

If your a/c clutch is pulling in for a short while and then dropping out, it's probably because the base unit is detecting a rotational speed error on the compressor. This can be caused by oil on the clutch plates, amongst other things. As far as your system pressure goes, 8 bar looks good at the sort of ambient temperatures you seem to have.

Mike

Celsius Mode it is!

1-31
2-23
3-35
4-34
5-35
6-51
7-7
8-45
9-65

MikeJT

· #5 · Sep 30, 2011

All those values look quite sane to me for a system that isn't running, assuming that your engine wasn't up to full temp - ECT (sensor #6) is only 51 degC: this value should agree with the temp displayed in the cluster.

You may have oil/grease on the clutch. I would suggest that you try spraying some degreasant - I use IPA (isopropyl alcohol) - into the gap between the clutch plates and see if that makes any difference.

Mike

JJRAGE

Discussion Starter · #6 · Sep 30, 2011

Thanks Mike, i'll give that a try. When i got the car, the AC worked intermittantly. The compressor would work for about 10 minutes, then disengage. Finally, it stopped completely except for when i first crank on the AC.

An inspection of the wiring to the top of the compressor revealed someone had done a wiring "hack job". There were 4 wires in the harness from the cars electrical system. 2 of them wires had the same color code and were twisted together. The other 2 wires had different color coding and were kept seperate.

So basically, what was 4 wires were now 3. The previous "backyard electrical whiz" that did this wiring job decided to add much smaller wires as extentions to the connector that plugs into the top of the the AC compressor. Nothing was taped, no wore nuts, no crimp connectors, shrink sleeve...nothing. Just twisted the darned things together and let em dangle under the car.

Oddly enough, it at least worked...part of the time lol. Upon complete failure of the compressor, and as soon as i saw this wiring nightmare, i re-did the wiring correctly. But to no evail.

So yea, this S420 restoration is gonna be fun, but hell, it's a 420 ya know?

Oh, not to mention i'm an Aries, and dont like to be outsmarted by metal and plastic lol.

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JJRAGE

Discussion Starter · #7 · Sep 30, 2011

I did notice something else. When i start the car with the AC off. The compressor doesnt engage, normal right? Without killing the car, i turn the AC on, the compressor spins for a few seconds then stops.

Without killing the car, i turn the ac off, then on again. Compressor doesnt spin this time, not even for a second. nada, nothing.

If i enter diagnostic mode on the AC head unit, the compressor spins for a second, then i get an E013 code. I delete the error code and hit the right "auto" button, it goes blank, re-reads the sensors and the compressor spins for about 4 seconds then stops. Then of course i get another E013.

The 3 wire connector on top of the compressor, does anyone know what each of the wires is for? as i said, 2 of them are the exact same color code and are strapped together. Basically, 4 wires from the harness go to a 3 pole connector on the top of the AC compressor.

JJRAGE

Discussion Starter · #8 · Sep 30, 2011

Also, the aux fans "never" engage unless the car is getting hot. AC on, or AC off, they dont come on unless car is pretty warm.

Reactions: 1

MikeJT

· #9 · Sep 30, 2011

Pin #3 on the compressor connector has 2 wires to it: one from the base unit supplying +12 V to the clutch coil and a return line to the a/c controller to tell it that the clutch is energised. The clutch coil gets its ground connection via the compressor housing. Pins #1 & 2 are connected to the rotational speed sensor on the back of the compressor. This signal is sent to the base unit which compares compressor speed to engine speed: if there's a significant difference the base unit assumes that the compressor has seized or the drive belt has broken so it de-energises the clutch.

If there is a speed error, in general, it will not re-energise the clutch without a key cycle. Sometimes if you wait long enough it will have another go but I think that this depends on the degree of slip it detected. I was unaware that it would have another go if diagnostic mode is entered.

As far as I know, the aux fans don't come on until an ECT of 100 degC is reached or a system pressure of 14 bar. Since you never reach 14 bar, 100 degC it is.

The fact that you appear to have a controller for a car with rear a/c but fitted to a car without rear a/c throws something of an unknown into this diagnosis, but I would still check the clutch plates first.

Mike

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JJRAGE

Discussion Starter · #10 · Oct 1, 2011

Tried the IPA trick, no luck. Im wondering if the speed sensor wire is at fault somehow.

Reactions: 1

JJRAGE

Discussion Starter · #11 · Oct 1, 2011

I took my Duovalve apart today. OMG, the gaskets had turned to goo. Took 5 spark plugs to cork the darned hoses till i can get a new one.

MikeJT

· #12 · Oct 1, 2011

JJRAGE said:
Tried the IPA trick, no luck. Im wondering if the speed sensor wire is at fault somehow.

Too bad. There are 2 sensor wires that run around from the back of the compressor to the plug on the front and then 2 wires in the loom back to the base unit in the module box. To check the actual sensor signal requires a 'scope, I think. Otherwise, you could check continuity through the sensor (I guess it's a magnetic sensor with a coil so should have a continuous path through it). You could also check continuity from the plug to the base unit. Trouble is getting to the base unit pins - #40 and #41. In the past, I have opened up the base unit and soldered on flying leads so that I could do checks with the unit plugged in. I did this to check the a/c controller signal to the base unit and the base unit output when my clutch was slipping and I couldn't understand what was going on!
Good luck,

Mike

MikeJT

· #13 · Oct 1, 2011

JJRAGE said:
I took my Duovalve apart today. OMG, the gaskets had turned to goo. Took 5 spark plugs to cork the darned hoses till i can get a new one.

A separate problem, I guess - one for the cold months.

Mike

JJRAGE

Discussion Starter · #14 · Oct 1, 2011

any idea what the order and color codes are for the wires that go to that black connector on the top of the compressor?

Im leaning towards speed sensor issues. All of the wires from the harness to that 3 pin male connector on top of the compressor were comepletely unprotected and groundable to each other, the compressor, etc. No tape, nothing..they were simply twisted together.

I have a feeling either the wiring is fried, the speed sensor took a dose of voltage from the wires being screwy and hencerforth fried, or the climate control unit inside the cabin took a dump, likely from 12V+ being dumped through the wiring into pins #40 and #41.

I hope its something simple lol. I agree with Mike on this, speed sensor related issue. OEM for compressor shows it has a speed sensor on lower side of compressor.

MikeJT

· #15 · Oct 1, 2011

JJRAGE said:
any idea what the order and color codes are for the wires that go to that black connector on the top of the compressor?

Im leaning towards speed sensor issues. All of the wires from the harness to that 3 pin male connector on top of the compressor were comepletely unprotected and groundable to each other, the compressor, etc. No tape, nothing..they were simply twisted together.

I have a feeling either the wiring is fried, the speed sensor took a dose of voltage from the wires being screwy and hencerforth fried, or the climate control unit inside the cabin took a dump, likely from 12V+ being dumped through the wiring into pins #40 and #41.

I hope its something simple lol. I agree with Mike on this, speed sensor related issue. OEM for compressor shows it has a speed sensor on lower side of compressor.

These purport to be the wiring diags for your a/c:

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1994/S420/SYSTEM WIRING DIAGRAMS/5173.pdf
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1994/S420/SYSTEM WIRING DIAGRAMS/5174.pdf

Diag 2 shows the colour codes for the loom wiring.

I personally would doubt that the a/c controller was damaged by s/cs on the wiring. The only connection between the base unit and the controller has either 12V or 0V applied to it by the base unit, so it probably wouldn't be too bothered by those voltages appearing from elsewhere. The a/c controller is still instructing the base unit to energise the clutch and the base unit is still trying to, which suggests the controller's alright.

Maybe the speed sensor is nbg - or even the cct on the base unit that handles the speed comparison may have been damaged. Don't know whether you can borrow a swop-out base unit to check the latter.

Mike

STARLINER W140

· #16 · Jun 21, 2013

as I see,this is an old subject,but I need some help,my ac was not engaging and the dtc was showing a31m1 problem... I solved it and deleted the code but it was again and again showing the same dtc code and the v2 matrix diode thing.... I decided to change the N22 with another one for testing purpose... (btw my some buttons were not functioning except I hit on them with a hammer)

,so I found one which is in so much better condition then mine,I tested it all the buttons are perfect working,also I heard the clutch engaging for the first time ever

but this lasted only for approx 3 seconds then stopped... the dtc now shows E0 13 (rear ac pushbutton connection problem) the fact is the car ı took thıs unit was equipped with rear ac,mine is not... te que : is it a reason for the ac compressor not to engage ?? or is the problrm somewhwre else? if ı solve the hidden problem,will it again be a problem for the comp to engage or not?? thanx...........

glenlloyd

· #17 · Jun 22, 2013

STARLINER W140 said:
as I see,this is an old subject,but I need some help,my ac was not engaging and the dtc was showing a31m1 problem... I solved it and deleted the code but it was again and again showing the same dtc code and the v2 matrix diode thing.... I decided to change the N22 with another one for testing purpose... (btw my some buttons were not functioning except I hit on them with a hammer) ,so I found one which is in so much better condition then mine,I tested it all the buttons are perfect working,also I heard the clutch engaging for the first time ever but this lasted only for approx 3 seconds then stopped... the dtc now shows E0 13 (rear ac pushbutton connection problem) the fact is the car ı took thıs unit was equipped with rear ac,mine is not... te que : is it a reason for the ac compressor not to engage ?? or is the problrm somewhwre else? if ı solve the hidden problem,will it again be a problem for the comp to engage or not?? thanx...........

The lack of a rear AC system should not prevent the forward AC from working. My control head, which might have been replaced, showed the same E0 13 error but worked fine after the compressor was replaced. I also tested another control head in the car and got the same error, but the car it came from did not have rear AC.

The error should not be a problem.

STARLINER W140

· #18 · Jun 22, 2013

glenlloyd said:
The lack of a rear AC system should not prevent the forward AC from working. My control head, which might have been replaced, showed the same E0 13 error but worked fine after the compressor was replaced. I also tested another control head in the car and got the same error, but the car it came from did not have rear AC.

The error should not be a problem.

Hearing this really made me feel better,today I will get it checked by mb scanner,and will hsare further issues

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