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Old 06-11-2005, 07:58 AM
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Question air conditioning problem 2003 s 430

i am getting a intermitent 12 volt signal to my a/c compressor on my 2003 s 430.the car was hit and the a/c condser,electric fan and drier have been replaced.it is a consistent on and off signal with the 12 volts coming and going approx every 5-10 seconds .also my electric condnsor fan is not coming on when the a/c is tuned on(should it?).the system was recently charged and checked for leaks.could this be a pressure switch prblem?if so how do you confirm bad pressure switch and where is it located.thanks


Last edited by jberling; 06-11-2005 at 08:12 AM.
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Old 06-11-2005, 07:15 PM
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I can help you partially. The cooling fan in front of the condenser (auxilary cooling fans) come on when the pressure raises above a certain point. This pressure increase will happen at idle. If the car sits for more than 5 minutes or so on a hot day and the fans don't come on, then there is a problem. I know our cars are different but A/C is still A/C.
You should be able to test the pressure switch by removing the two wires from it and touching them together. If the A/C is on, the fans should then come on as you are completing the circuit. My pressure switch has two wires, Im not sure about yours as I've never looked closely under the hood of a 220. The pressue switch will be a small cylinder looking piece that is about the size of 8 quarters stacked up. It will have an electrical connection going into the top of it. First place I would look is your drier as that's where MB usually puts it I believe.

Regarding the power coming on then off, it sounds as if you have a low charge to be honest. That could cause all your problems. I think there are two different pressure switches? One controls the aux. cooling fans and the other will control the compressor cut-out. The low pressure switch cuts the power to the compressor if there is low pressure. Low pressure would be a result of a low charge. If there is not enough pressure (thus not enough refrigerant) then there is a shortage of oil. The oil is mixed with the refrigerant so when the refrigerant leaks, so does the oil. This switch could probably be tested by once again jumpering the two wires together and see if it stops the compressor. To me, it seems like your compressor is short cycling because of the low refrigerant and the other switch (high pressure switch) isn't being activated because with the low refrigerant, the pressue doesn't get high enough to trip that one off.

So, in reflection on my long post, take it to the dealer or A/C shop and have the pressure checked. They'll hook up guages and can tell what your pressure reading is at and the dealer could tell you what the pressure should be at to trip the different switches for their individual function. If you lived closer I'd come over and help you out for a Pepsi (The dealer will charge more than a Pepsi for their service)

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David
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Old 06-11-2005, 08:56 PM
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thanks.- there are two pressure switchs mounted on top of the drier.ones has 3 leads and the other has two.if i unplug the one with the 3 leads, the fan comes on.if i plug it back in the fan shuts off.as of today i no longer have any juice going to the compressor and the a/c light on the interior control panel that indicates the a/c is off stays on. in other words my problem went from bad to worse
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Old 06-12-2005, 01:38 AM
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Perhaps the constant light is some sort of code? I think you need to take it to the dealer and have them check the charge. It sounds as if your high pressure switch is working correctly as is the fan/s,

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David
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Old 06-13-2005, 09:15 AM
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thanks
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Old 06-13-2005, 10:29 AM
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Let us know what happens after you get it checked/charged correctly.

Thanks
David

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