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Discussion Starter #21
Thanks Kajtek1.

Do the error codes i posted provide any guided clues?

Not Sure that I am avoiding proper troubleshooting, I think its more of a case of not knowing what to do and limited to the tools on hand. I am trying to avoid dealing with all possibilities, if I can.

Are the DTC codes of any use at all ?

Does the fact that refrigerant pressure is very high on the low side with the AC set full ON and at the lowest temp any indication of what might be wrong? -- seems like there is enough refrigerant in there. BTW the AC was not working before I change the cabin air filters and is not working afterwards, so I have rued out that event as a possible cause.
The AC compressor is turning as well as the pulley in the center.
 

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The error codes are not relevant to the AC cooling properly. The sun sensor just recognizes if the sun is hitting the car or not and it will adjust the fan speed based on how intense the sun is.

The coolant pump is designed to help circulate coolant through the heater cores when the engine is idling. It will also circulate coolant through the heater cores when the engine is off when you press the rest button. So you can get warm air blowing even with the engine off depending on what temperature you set the climate control to. It will also run for either 5 or 10 minutes after the engine has been turned off depending on coolant temperature. If coolant temp is 215F the pump will circulate coolant through the system to help prevent hot spots and to cool the engine. If the coolant temp is 230F the pump will run for 10 minutes.

Also I posted the instructions for the test.
 

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Discussion Starter #24 (Edited)
I appreciate Kajtek1 and Illstplaya's help:
With the engine hot, I have the following:

Hot Cold

1 96 75
2 84 71
3 109 82
4 109 82
5 107 80
6 179 85
7 09 05
8 112 76
9 27 27
10 4.5 1.4
11 1.3 1.1
12 4.3 4.3
20 3.2 3.2
21 32 32
22 0 0
23 32 32
24 11.1 11.3
40 164 164
41 85 85
42 40 40
43 136 136

These are the readings with the engine cold and the engine hot.
Hot -- after being driven for about 40 mins
Cold --first thing in the morning in the garage.
I hope these are clear.
 

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Discussion Starter #26 (Edited)
The hot part should be with the engine AND a/c running, engine idling.
The readings are as below. Outside temp is at 80 F. The AC seemed to be working again but clearly was not, yesterday when the temp was 85 F outside.

1 69
2 78
3 48
4 46
5 48
6 191
7 10
8 103
9 35
10 1.6
11 1.2
12 3.4
20 3.2
21 44
22 0
23 32
24 13.3
40 164
41 85
42 40
43 136

Seems like I have an intermittent problem somewhere.
 

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Hey dilsingh:

I noted on both my e320 and ML500 that when adding freon (just plain can of R-134a, no sealant, no pag oil) that if the pressure indicated on the gauge went too high, the "overpressure" switch would cut off the AC output.

For example my "Trigger AC Dispenser Hose with Gauge" would show between 25 and 45 PSI and freon was freely flowing into system (indicated by rapidly cooling 'sweaty' can & cool air from AC Vents in car) things were good. But, of course, I tried to overdo it and when one can ran out, I tried adding another, and then when the gauge indicated over 45 PSI (upper limit of 'Green zone'), then the AC Output ceased & system blew hot air !
I quickly sensed what I had done wrong - gone over pressure limit, which appears to be 45 PSI with engine running & system on HIGH.

So, to Youtube to find out how to bleed pressure back down, it wasn't too hard * - and once I bled it down below the 45 PSI setting, immediately Cold Air began flowing from the vents.

So be aware that any pressure over the cut off # will have that negative effect of cutting off the AC totally.

If you suspect that's what's happened maybe just YouTube how to bleed / reduce AC pressure when accidentally overfilling Freon !

Hope this helps - David in East Texas
 

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The readings are as below. Outside temp is at 80 F. The AC seemed to be working again but clearly was not, yesterday when the temp was 85 F outside.

1 69
2 78
3 48
4 46
5 48
6 191
7 10
8 103
9 35
10 1.6
11 1.2
12 3.4
20 3.2
21 44
22 0
23 32
24 13.3
40 164
41 85
42 40
43 136

Seems like I have an intermittent problem somewhere.
What were the target temperature settings on the climate control ? 72 72 or LO LO. The in-car sensor indicates 69, so you should do the test with temps set to LO LO.

With your aux coolant pump not working, the tempering (trying to attain the target temperatures) will become a challenge for the controller, and I do not know, whether it even attempts to do that if one of the components of auto temp control is faulty (the others are the do valves, tempering flaps, heater core temp sensors, and the in-car sensor). So setting to LO LO will eliminate the tempering issue, and the climate controller will try to cool as best as it can.

The high side pressure is seems to be low at 10 bars, but then again this value fluctuates during tempering process. So get the value when the setting is at LO LO (if already it was not).

Also measure the low side with your manifold gauge, when the engine is warmed up, a/c running,
 

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Discussion Starter #29 (Edited)
I had set the temp to 64 F on left and right.
I will repeat tonight with LO LO

I measured the pressure with the gauge that comes with the Freon can and it indicated a pressure that is almost as high as the meter can read -- needle to the extreme right.
 

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10 bars on working AC is low pressure.
To follow up on hot test, when you come in hot afternoon, turn ignition on, display #7 refrigerant pressure, start the engine and observe the pressure change for next couple of minutes while driving.
Your sensors when cold show 14 degrees difference. A bit extreme, so maybe the car wasn't completely cold? Try to repeat that?
 

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I had set the temp to 64 F on left and right.
I will repeat tonight with LO LO

I measured the pressure with the gauge that comes with the Freon can and it indicated a pressure that is almost as high as the meter can read -- needle to the extreme right.
You need to read it when the a/c is running. If the a/c and the engine is not running, that reading is the static pressure and could be around 80 to 100 psi which reads in the "red" zone in your can-meter. When the a/c is running and stabilized (5 minutes), the reading should be in the "green" zone, around 25 to 30 psi. "Yellow" zone indicates some overcharging, and if the reading is in the red zone when the a/c is on, you likely have a compressor issue.
.
 

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Discussion Starter #32 (Edited)
I saw the following readings with AC turned to LO,LO, after driving for about 30 minutes with engine idling.
Air coming from vents was cold.

1. 73
2. 75
3. 58
4. 60
5. 46
6. 197
7. 15
8. 127

35
5.7
1.1
4.3
6.7
44
202
13.1
164
85
40
136
 

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Discussion Starter #33 (Edited)
I see the reading is on the green zone. Its close to 50 PSI according to the gauge that came with the Freon filling can.
However, if value 7 indicates the pressure then that is a value of 14/15 -- PSI when the AC is running and cooling.
Both DUO valves are very hot and the hose from the AUX pump to DUO valve and compressor(?) is also quite hot.
All of the AC parts are original and about 18 years old.
 

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Discussion Starter #35 (Edited)
No Sir, I do not have time to fool around. I am trying to understand why the AC was not cooling when the temp was at 86 F outside.
When I posted the above measurements, I had turned the AC to LO,LO -- so even if it was 73 the car AC should be cooling.
I am hoping NOT to study the cooling system to the nth degree to fix the problem, if possible.

I connected 12 V directly to the AUX pump and it was running fine.
I connected a 9V battery to each of the DUO valves and could hear the solenoid actuating.

If other respected people think I am just fooling around please let me know and I will stop posting immediately and not waste anyone's time!
 

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You may have a working aux coolant pump when you apply 12V across the terminals. Obviously the climate controller. which supplies the voltage to the pump does not see it. The reason you get that fault message is because the controller wants to see 2 to 4 ohms pump resistance, when it tests the pump at the controller end. So you may have some wiring or connectorization problem.

Regarding the LO LO measurements, and the low side refrigerant pressure of 50 psi... I do not really trust these gauge on the top refrigerant cans. It is much cheaper to get a gauge that one side screws into the $4.88 Walmart special R134a can, and the other goes to the low side valve. In any case if what you measured is correct at 50 psi at the low side with the a/c and engine running (stable), it is too high. It should be less than 30 psi or 2 bars. Have a look at graph B on the right side with the ambient of 25 degrees C.

STAR TekInfo

This is where "one-finger" wizardry ends, and the real stuff starts.

You may have an issue with the expansion valve not closing as it should, or the inlet valve of the compressor is restricting the flow to the compressor cylinders to be compressed.

It would be a good idea to take the readings when you experience "no" cool" condition when the ambient is 85 degrees F or above.
 

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I takes 60 seconds in the morning and 60 seconds in the afternoon restart and post the numbers to troubleshoot the system for 90% of the problems and sometimes additional 2 minutes to follow up on compressor performance. .
So all it takes is about 3-5 replies to have good results when one follows the procedure.
Now here, we are on reply 37 and we still lack troubleshooting data.
 

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Discussion Starter #38
Thanks guys.
I have really tried to do my best, but its not good enough.
I will take it to someone who can look at it physically and perhaps has the tools and skills to fix it.
 

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I think that is an excellent idea. Make sure you take it to a workshop who is experienced in MB climate control systems (who knows a difference between a pressure switch and a pressure sensor :)). Typically, by just looking at the high and low pressures with a proper manifold gauge, the problems will be evident, and the sensor values and fault codes will be able to show where the problem "may" be.

I had already posted a link regarding the refrigerant test program from MB (Startek link), and the technician will likely follow a similar testing steps. If they are equipped with MB SDS (diagnostics scanner), they should be able to actuate your aux, coolant pump, duo valves, compressor, cooling fans, etc. . to test whether they work as they should.

Sometimes evacuation, vacuuming and recharge with correct amount of refrigerant will do the trick, especially if moisture and air was introduced into the system during charging, at some point.
 

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Well, over 90% of members who took their MB to AC specialist report butchered service.
Not too many shops learned how to service computerized system with 8 sensors making it working.
It is learning curve how to read the data on climatronic, but than pushing the buttons is not a rocket science.
It is following the protocol that seems to be a problem here.
We ask for climatronic AC data and we got can gauge or heating data instead.
This topic has lot of misguidance and moderation in it, but that is how the internet works.
It is another learning curve to pick topic essentials from the replies, while skipping the side comments.
And again - stickies have most of those things covered pretty well.
 
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