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  #1  
Old 06-03-2001, 10:04 AM
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Just had two different techs look at the A/C on our1987 300 SE(euro).
When highway driving the car takes it's time but does get nice and cool(just cool and pleasant - not cold). In the city stop & go traffic which we do a lot of - forget about it. It really doesn't cut it.

The first tech looked at the sight glass, poked around and said that all the car needed was more R-134 .
The second guy was more thorough but less conclusive. He checked the system under pressure and did not think it was lacking gas. He said the mono valve is good, the main flap does close,the pressure switches seem fine - the fan works(even though it does not come on automatically when the air is on ) The engine runs comfortably just above the 80C mark and the A/C does not seem to put a big strain on it in terms of heating up.
But it does not get very cold. As a matter of fact, when the RPM's drop as we shift into gear from park - the temp. rose on his digital gauge by a few degrees C.He was not sure about that. The one thing he did suggest was changing the green system(pressure switch..) to a red one - that get's the Fan going earlier than 107C, thus helping the A/C in warm climates. Anyone try that before ? or know about It?

a seperate question - the vent for the back seat passangers will only blow hot air-all the time, no matter what. Is that a vacuum problem? how can one track it ?

Gotta love this forum..
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  #2  
Old 06-03-2001, 12:07 PM
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Well my first reaction is that your system is working properly. The early 124 cars make absolutely the worst conversions of any of the hundreds we have done.

If I forget about the obvious, I would go next to the recirculate door activation. It is a two stage vacuum actuator. It is usually somewhat closed at first stage. It goes fully closed at full recirculate. If the door is open the duct temp will be anywhere from 10-15 degrees higher than it should be.
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  #3  
Old 06-03-2001, 01:06 PM
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thanks for the speedy reply Steve. If you are refering to the main flap(Ibelieve you are) behind the glove compartment - I pulled those actuators out a while back to inspect them. they seem to work OK and so does the flap - the recirculation switch on the center console sometimes cuts out (I cleaned the contacts,like many of the threads suggest, but it still does that intermittently - I should probably replace the switch).
You do not think then that I should evacuate the system and recharge it ?

Also , any thought about the passanger vent pushing hot air? that seems like a mystery. The first tech I had spoken to said recharging the A/C would take care of that - the second said it had nothing to do with anything of the sort.
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  #4  
Old 06-03-2001, 01:48 PM
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It is so hard to find the appropriate names for the different doors. The flap that has two elements is not the door I'm talking about. The recirculate actuator has two vacuum lines to it and is in the center. It closes the door above the blower. The first one I found by blocking the door under the hood. (I don't actually do the work so I'm a little rusty on actual locations). I am involved with the diagnostic plan all the time and I remember we tested the first one by blocking the door from the outside.
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  #5  
Old 06-03-2001, 10:10 PM
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If your car is converted to 134-a, you can forget about that cold A/C that your car once had.

The only way to get it cold is to find the leaks, correct them, then go back to 12.
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  #6  
Old 06-04-2001, 04:36 AM
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the conversion was done by a previous owner...so what can I say.
Still I'd like to ask Steve whether I should investigate under the dash for that recirculate door he mentioned -
the A/C DOES come out of both center and side vents, no problem.(from the many threads I read I know that is a common problem)
it just feels like a desert cooler....
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  #7  
Old 06-04-2001, 09:35 AM
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Some points I would consider:

If ,as you say, the aux fan does not come on with
a/c, that is an indicator of slightly low freon.
[not enough high-side pressure to trip switch]
Try jumping the switch.
If fan comes on, pressure is low/or bad sw.
If fan does not , possible fuse/relay etc.

The 107C you mention is not an a/c fan switch. It is the engine temp coolant high speed fan . Changing the a/c pressure sw has nothing to do with the 107C cut in.

As stated, 134 conversion results in poor cooling compared to 12. However , there is also the remote possible that the system was not properly evacuated and has some air in system. I mention this because you have stated that a tech said you have good pressure readings. Good readings and poor cooling will result if this is the case.

I am also assuming that the first tech stated low fren after looking at the sight galss. Check that first.
The difference from poor cooling to adequate can sometimes be just a few ounces of freon. That would be my first try.


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  #8  
Old 06-04-2001, 02:38 PM
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I had inquired about evacuating the system because I had read about that in many of the threads. I recall reading that it was very easy to overfill the system which is not a good thing to do - and that there was no way to measure adding just "a Little".
Is that correct ? If this is a good direction to go - I would love trying that for starters, rather than tearing into the dash.....
BTW the fan was jumped and is good.
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  #9  
Old 06-04-2001, 02:46 PM
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So the fan is OK. But you said it does not come on .
That indicates low freon/bad sw.
Without gages, you now want to look at the sight glass when a/c is on and around 1500 rpm.
What do you see?
[sight glass is on top of drier/reciever. Que-tip clean up is helpful here]
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  #10  
Old 06-04-2001, 05:31 PM
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The electric fan(s) not working would cause your exact symptoms. It should come on a few seconds after the the compressor comes on when it gets up to operating pressure. Remember cooling at slow speeds (car and engine) is the worst case condition for the air conditioner. Sometines when I'm stopped in traffic I'll rev the engine up a little to about 1000 or 1500 rpm to keep the compressor and fan spinning a little faster, that seems to help a little. It brings the oil pressure up too.

And a question: Is this a new condition or has the car always done this?

I noticed you have a 380 SE euro. When I was looking to buy a Mercedes I looked for standard transmissions. I found one just like yours with a 5 speed, but it was too big and too much for me.

[Edited by Jim Anderson on 06-04-2001 at 04:37 PM]
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  #11  
Old 06-04-2001, 06:33 PM
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Jim-I got the car just a few months ago - early spring , so I don't know whether it was always like that.previous owner told me A/C was fine.Being spring , it did seem fine... It is actually a 300SE(automatic) rather than a 380.

Arthur - Is there a way to tell a bad switch ? or is it trial & error.I'll check the sight glass at 1500rpm tomorrow. any hints ?
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  #12  
Old 06-04-2001, 07:23 PM
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If the sight glass is foamy/lots of bubbles,
it is low on freon. Very few and almost completely clear is what you want.
The sw. test would need gages for pressure readings.
If the freon needs topping off, the fan sw. will then work as the pressure will be back up to normal.
Be aware that the fan is more likely to come on with higher ambient temps. If it is cold outside , it is possible for the fan not to be called for.

Some guys actually wire a switch in the cabin that jumpers the pressure switch and use it at their own discretion.
I used to do that to all my old Benz so I could get a jump on the heat. Also nice if in traffic/up- hills , etc. when the temp. gage starts to creep up there.
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