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  #1  
Old 04-29-2003, 01:20 PM
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Angry W201 A/C Upgrade

I have an 87 190 2.5 Turbo Diesel and I've recently put on a rebuilt compressor, some new hoses, and a dryer. I'm puzzled that it still seems to lack cooling ability in stop and go traffic.

The system is still R-12.

Is there something else in the system that could cause poor cooling while sitting still?

Any help is appreciated! Thanks!!

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  #2  
Old 04-29-2003, 01:52 PM
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Well from all of the 190D owners I know, they say the AC really is weak. Your system should be the same as it was before you replaced those parts, that is unless you upgraded them. Such as a bigger compressor and higher capacity evaporator would provide better cooling. I feel it is not worth it to go through this extensive work, unless of course you have lots of money, time, skills, and live somewhere that is hot. According to my performance products catalog for the 201 chassis, every 190D model (2.2, 2.5, and 2.5T) all use the exact same AC system. So all of ours suck.
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  #3  
Old 04-29-2003, 01:52 PM
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There should be an electric fan in front of the condenser that comes on at a certain temperature or pressure to move air through there. They're known to fail, and if it's running you should hear it easily.

The title of your post contains the word "upgrade," but you didn't make it clear whether you're looking for a further upgrade or you consider the work already done to be an upgrade.

If everything is working as designed and that still isn't enough, then yes there is an upgrade. Later models had two smaller electric fans instead of big one. Fitting them to your car would also involve modifying the radiator support, but it has been done.
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  #4  
Old 04-29-2003, 01:56 PM
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Actually, my 190 already has dual cooling fans. I guess it's as good as it's going to get.
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Old 04-29-2003, 02:09 PM
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Ok then, some more questions. Please do not take this as insulting - it is not meant to be. Have you done AC work before? What are your pressure readings and duct temperature? How long did you evacuate? When LarryBible, our resident AC advisor, read this he will want to know these things.

This could also be a bad expansion valve. They're very delicate and prone to corrosion if the system was open for a while.

I used to own a 1986 190E, and it cooled just fine in central Florida, so I disagree with the opinion that "they all suck." One promlem I did have was that it would occasionally go to full heat. The pushbutton controller can be screwy that way. If you think that might be a possibility, maybe you can bypass the heater core.
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Old 04-29-2003, 02:17 PM
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No offense taken. I'm not an A/C mechanic, but my brother is on GM products, so I was under some supervision.

The system was evacuated for 30-40 min. The high side pressure is around 200-225. I don't recall exactly. I know that there was some question as to whether the fans were kicking in so I watched the pressure and they do kick on around 250, I believe.

I don't recall the low side pressure.

I haven't checked the inside temperatures yet, but I haven't had a problem with hot air at the side vents.
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  #7  
Old 04-29-2003, 02:28 PM
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Off the top of my head, 250 sounds awfully high for the fans to kick on for an R12 system. Some of this is starting to come back to me - there are two versions of the pressure switch, a green and a red I think. One of them is of R134A conversions, so you may have the wrong version of that switch. A search through the Tech Help archives should help you.

The fans are pretty noisy, so you should hear them in the cabin. Without them on, you're not going to get much out of the system.

That's the last I'll say about this one - will defer to someone who has more practical experience. Finally, (joking) your brother is an AC mechanic? Why the heck are you asking us questions?!!
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Old 04-29-2003, 02:32 PM
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  #9  
Old 04-29-2003, 02:54 PM
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There is a pressure switch on that car, which triggers the electric auxiliary fans based on refrigerant high-side pressure. The stock switch is green colored, and has a stupidly high setting - comes on at 20 bar, and turns off at 15 bar (that's roughly 300psi and 225psi). Meaning the fans will almost never run. Mercedes later superceded this switch with a newer one, that is red in color, and triggers on at 16 bar and off at 12... which is a huge improvement. The switch is cheap, maybe $30, but screws into the receiver/drier and requires - you guessed it! - evacuating the system to replace it.

I don't know how much difference this will make, but if you have the green switch, swapping to red may help at idle or very low vehicle speeds - it will NOT help at freeway speeds. The other thing to check is the vacuum operated pods behind the dash, that open & close the vent flaps. If your recirculation pods have failed, you'll never get "max" cooling. You need a MityVac to test them, easiest from the multi-outlet valve assembly (not sure where this is on a 201 chassis, but it's behind the glovebox on a 124).


Good luck,
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  #10  
Old 04-29-2003, 03:08 PM
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I do have the red switch, but does around 250 still seem high for the fans to come on? Also the temp wheel has to be on "MIN" before they come on. Could my switch be malfunctioning?

Does the multi outlet valve have all the vacuum lines plugged into it? If it does, I've seen that behind the glove box.

Off and On I do get a loud clunck from the center of the dash. Could this be the vent flaps stuck?
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  #11  
Old 04-29-2003, 03:18 PM
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To test the switch, you'll need manifold gauges, and see at what pressure the fans turn on. Should be 16 bar, or about 240psi. Temp wheel should have NOTHING to do with this. The multi-outlet valve does have numerous vac lines attached to it. You pull one at a time and apply vacuum with a MityVac. Each should pump down to ~25 inches vacuum and HOLD that. If not, most likely the diaphragm is torn inside the pod for that vacuum line. Photos of my 124 pod replacement are here:

http://www.meimann.com/images/mercedes/W124_dash/

The clunk could be normal, or not - test as mentioned above...

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  #12  
Old 04-29-2003, 04:36 PM
LarryBible
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The pressure at which the fan turns on will have some effect on the cooling efficiency, but that is not why it is there. It is to protect the system from excessive high side pressure.

At this point you need to do a performance test. This involves measuring temperature in front of the condensor and temperature at the inside cooling vent. This is after stabilization of the system running full cooling setting and max fan speed and with engine at about 1500RPM. You should also monitor low and high side pressure. With these four parameters; low side psi, high side psi, condensor ambient and inside vent temps, we can go to the tables to see where we're at.

Also the low and high side pressures will give an idea about the condition of the expansion valve.

Have a great day,
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  #13  
Old 04-30-2003, 01:18 PM
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Larry's right-

You need to investigate throughly. I've seen evaporators that were really dirty and a no-wash cleaner too care of it. I've seen nearly dead condensor fans...
If you were doing an improvement- it would be a better condensor to get rid of the heat.
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  #14  
Old 05-02-2003, 02:44 PM
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I guess you can't always follow the owners manual. It stated to keep the dial around 22 C. I've been turning the wheel lower and using the recirculate button and it's cooling fine.
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  #15  
Old 05-02-2003, 03:10 PM
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Tee hee. I love it.

One other thing while we're on the subject. Check the little grate where the cabin air temp is monitored. It should be drawing in air. If not, the connecting tube or the motor may be bad. Sorry, but I've forgotten where this thing is on the W201.

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