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1999 E300 TD
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46 Posts
Discussion Starter #1
Hello,

This is my first post but I have been browsing through this forum for a while now.

I am having a little trouble with my a/c on my '99 210 E300TD. I started noticing the system would cool better at idle then it would going down the road.

I did a proper evac and recharge today, the system was about a 1/2lb low on refrigerant. I started it up to check the pressures and everything looked good at idle. Low side was about 30psi and the high side was around 200psi. Numbers aren't exact. When I gave the engine some revs in park the high side pressure started dropping down to under about 150psi. When the pressure dropped the air in the cabin would start to go up a few degrees. From about 45F to almost 60F. The low side seemed to like to stay around 30psi but would come down a little when reved. I was wondering if anybody else has seen this and if they know the remedy. I'm hoping it may just be a problem with the expansion valve and hopefully not the compressor.

I'd also like to add that the compressor stays on when the pressure drops, the condensor fans work when they are supposed to, the charge is 2.2lbs (I didn't just jam some pep boys cans in it) and the sensor readings all seem to be ok.

Thanks for any input.
TDP
 

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E320/E250 Bluetec Ford F350 6.7l
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36,710 Posts
Those systems work excellent with lower refrigerant pressure.
You posted the numbers but not giving us the circumstances.
200psi = 14 bars, what is on low side, but not bad.
Display sensor (#7) readings on your clima LCD and observe it during driving.
 

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1999 E300 TD
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46 Posts
Discussion Starter #3
Idle with a/c on in park -
High Side = 200psi or 14bar
Low Side = 30psi or 2bar

1500 RPM a/c on in park -
High Side = 150psi or 10bar
Low Side = 30psi or 2bar


The car doesn't need to be moving for the a/c to drop out.
The compressor also stays on.
 

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Outstanding Contributor W221 Moderator
2010 E350 P1/P2, 2008 S550 Designo, 2002 ML320
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1,983 Posts
Kaitek has it right, need the values from the ACC to help us understand what's going on.

As for the compressor, they do stay engaged as long as there is adequate refrigerant and not too much pressure. From what you are saying, it seems the system may be working properly. It would depend on what your interior temperature is set to, what your system 'thinks' the interior temp is, and whether you might have any defective components as well.

When the temperature the system is set to is achieved, the pressure in the refrigerant circuit is backed off via the control valve. If the inside should warm up again, the pressure is increased until you once again reach your target temperature. You might try setting the temp lower if the inside of the car is too warm when the pressure starts backing off.

Test values will help sort out a lot of this. Good luck!!
 

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1999 E300 TD
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46 Posts
Discussion Starter #5
ok guys, i pulled the numbers today.

It's about 90F with a million % humidity.
The a/c isn't cooling well at all today at idle or with the engine reving.
It's blowing between 55-60F out of the vents.

At first glance it looks like I may have an issue with the good old evap temp sensor but here are the numbers anyway.
The value for 21 also looks wrong, the first set of numbers are at idle and the second are at 1500RPM.

I guess i should also note the only code is for the coolant recirc pump, but what 210 doesn't have that code?

Values at idle in my driveway set at low on both sides
1 - 82
2 - 100
3 - 53
4 - 51
5 - 134
6 - 164
7 - 16
8 - 139
9 - 31
10 - 2.7
11 - 1.6
12 - 3.8
20 - 12.1
21 - 42
22 - 00
23 - 32
24 - 13.1
40 - 164
41 - 85
42 - 72
43 - 136

values at 1500 rpm in my driveway
1 - 85
2 - 103
3 - 51
4 - 49
5 - 130
6 - 163
7 - 13
8 - 141
9 - 31
10 - 2.7
11 - 1.7
12 - 3.8
20 - 10.3
21 - 58
22 - 00
23 - 32
24 - 13.3
40 - 164
41 - 85
42 - 72
43 - 136
 

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2001 E430 4matic
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419 Posts
Easy fix :) evaporator temp sensor needs replacement. If you adjust on hot, tap slightly few times the pump and then delete the fault codes, pump may work too.
 

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Premium Member
2001 E320 - Brilliant Silver/Ash: 107,000+
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17,193 Posts
Eagleone, would you mind explaining how you arrived at that diagnosis? I do not doubt you, I just want to understand which number(s) told you that.
 

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99 E430, 01 E430 Sport, 00 SL500
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3,266 Posts
When the evap sensor failed on my car, EC light came on, and there's a fault code stored.
 

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E320/E250 Bluetec Ford F350 6.7l
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36,710 Posts
I got pretty good in troubleshooting and fixing AC on those cars, but the refrigerant sensor is still a mystery to me.
Now having 2 cars to compare, the sensors show like 100+F difference between one car and the other, yet both systems work pretty efficient although both have occasional glitches when the computer switch one side to heat giving us 140F. Restarting the ignition usually fix that.
Reading the above, we still don't have variations of pressure during driving, but comparing 16 bars at idle and 13 at 1500 rpm points to low refrigerant. The system works, but not good enough.
No guarantee there is no other issues, but adding a can of R134 should be safe at this point.
 

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2001 E430 4matic
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419 Posts
Eagleone, would you mind explaining how you arrived at that diagnosis? I do not doubt you, I just want to understand which number(s) told you that.
Values at idle in my driveway set at low on both sides
1 - 82
2 - 100
3 - 53
4 - 51
5 - 134

#1 in-car temp sensor reads 82, left& right core temps reads 53,51, at this point your evaporator should be definitely colder than 53,51 in reality. However, evaporator temp reads 134 which is even warmer than temp inside the car of 82, even warmer than outside temp of 100 and warmer than left and right cores. This would conclude that evaporator sensor is faulty and shows wrong temp. In a way mostly trouble shooting these readings is evaluating the validity of the sensor readings. I hope that helps.
 

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12 GL450
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13,900 Posts
Values at idle in my driveway set at low on both sides
1 - 82
2 - 100
3 - 53
4 - 51
5 - 134

#1 in-car temp sensor reads 82, left& right core temps reads 53,51, at this point your evaporator should be definitely colder than 53,51 in reality. However, evaporator temp reads 134 which is even warmer than temp inside the car of 82, even warmer than outside temp of 100 and warmer than left and right cores. This would conclude that evaporator sensor is faulty and shows wrong temp. In a way mostly trouble shooting these readings is evaluating the validity of the sensor readings. I hope that helps.
Thank you for this explanation!:thumbsup:
 

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E320/E250 Bluetec Ford F350 6.7l
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36,710 Posts
What I could never learn is where is the evaporator temp sensor placed.
If it is on high side (before the nozzle), the 134F would be normal, if it is on low side, that would indicate malfunction. As I said, on our two W210, one sensor shows low, the other high but this is not stopping both systems from freezing our elbows.
 

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1999 E300 TD
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46 Posts
Discussion Starter #16
I popped in a new evap temp sensor and now the value for it is correct.
The system still isn't working gangbusters but it is good enough to get me through the season, I have a steady 50F coming out of the vents now and the pressures seem to be staying where they should.
The a/c never really worked great but now it's working better.
For a car with 300k it works fine and winter is coming anyway.

Thanks for all the helpful responses.
-TDP
 

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1999 E300 TD
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46 Posts
Discussion Starter #20
your pressure readings show too low pressure on high side.
Might be worth putting a gauge on low side and troubleshoot the compressor.
That is what I was thinking from the start until I saw the evap temp sensor reading. I'm not too worried though, the car was comfortable today in high humidity and 90+ heat. I'm just kind of tired of working on it for now, I just did the sway bar bushings and links, all the fluids and all the filters, front brakes, new seat, tail light and a couple other things I can't remeber.

No more work time to drive.

-TDP
 
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