1995 E320's AC has quit working I pulled out the climate control relay behind the battery to give it a look. I then jumped the two prongs that basically straight wires the compressor and plugged it back in. The compressor came on just like it should, so I thought that my relay had just went bad. I ordered one from Mercedes and installed it and I still have nothing. With the new relay if I just barely sit it down on the connector it will engage the compressor for just a second then disengage. When you plug the new one all the way in it does nothing. I know I have the right amount of freon in the system because I checked it when I had jumped the old relay. I don't know what else to do I don't want to leave the compressor straight wired because it will run all the time. Does anyone have any ideas to what my problem may be?

Maybe one of the fulltime mechanics here can verify this...

On my 98 E320, I had the same symptom. When energized, the compressor would run for just 2-3 seconds, then shut off. The fact that it starts at all indicates it's not the freon pressure or the switch.

Using the diagnostics built into the temp control computer, I determined it was the evaporator temp sensor. The reading was way out of whack.

I don't think the 95 has this diagnostic feature. Anyway, I later read on here that the evap temp sensor on my car is a very common problem. And it was very cheap to replace. It's located right above the driver's feet.

Hey, now you can help me ;-)

I don't know if our engines are the same or not, but if they are similar, it would be of great benefit to tell me where the vacuum hose goes that I describe in this thread:

http://www.peachparts.com/shopforum/showthread.php?t=248324

Thanks

No my car doesn't have the diagnostic feature your describing in the W210 chasis. I will look and see if I can find the line your talking about. Anyone have any more suggestions on my AC problem?

Even if you don't have the diagnostics built-in, it still sounds like the evap temp sensor. It was easy to fix, once I found it.

Well, I may be wrong. I went to the parts link on here to see if the 95 and 98 use the same part number for the evap temp sensor. For the 95, it does not list an evap temp sensor. Opps. Sorry about that.

It does list temp sensors, though. The one on the receiver tells the aux fan to start. Not likely that one. But it also lists one for the engine block. Apparently, if the block goes higher than 130C, it shuts down the compressor. That sensor might be bad, or disconnected.

For RTDs (resistive temp detectors), the resistance goes up as the temp goes up. So if it's unplugged, the computer thinks the engine temp is high, so it shuts down the compressor. Also, if the element inside an RTD breaks, it thinks the temp is very high. If you can locate it, see if it's unplugged. If it's not unplugged, unplug it and measure it's resistance with an ohm meter. If it indicated infinity, it's bad. Make sure you're working on the right sensor, though.

The parts page says it in the intake manifold, and the base is blue in color. Look here: http://catalog.peachparts.com/ShopByVehicle.epc?q=1995-Mercedes--benz-E3--0--Sedan-Climate--Control&yearid=1995%40%401995&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6392%3ABT%7C5%3AMBC%7C1508%3AED%7C10000022%40%40E320+Sedan&catid=242213%40%40Climate+Control&subcatid=242256@@A%2FC+ACC+Temp+Sensor&mode=PA

< the resistance goes up as the temp goes up. So if it's unplugged, the computer thinks the engine temp is high, so it shuts down the compressor. Also, if the element inside an RTD breaks, it thinks the temp is very high.>

Just the opposite.
That sensor is a NTC [ Neg Temp Coefficient] thermistor sensor..as temp increases , R drops.
The open circuit is simply an Aux Fan Default from the ACC panel circuit.

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A Dalton

The problem occurs no matter if the car is hot or if I just cranked it up for the first time of the day. It doesn't seem to matter if the engine is warm or cold. Arthur D do you have any suggestions?

Does your car have a compressor speed sensor?

Im not sure??????

Compressor speed sensor and K40 relay will shut down the compressor if the belt slips.

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Gone to the dark side

- Jeff

If the engine over-temp sensor is a thermistor, instead of an RTD (I have no reason to doubt that), Arthur is exactly right. It could still be this sensor, though. Try unplugging it. Troubleshooting doesn't get much easier than that.

I will do that today and see what happens

BigRed0803 Could you show or tell me how you jumped relay on your 1995 e320? Im getting no power to compressor...