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With summer approaching (which lasts about 6 weeks here in the Pacific Northwest), I decided to turn my attention to the A/C in the '94 E320 (v2.0, the one I bought last November).

The blower happily blasts away ambient air with the A/C cranked up full. So the first thing I did was open the Schrader valve and plug in a can of R134a, figuring it might need a recharge. Imagine my surprise when I found that the system pressure already registers 100 psi. Thinking the cheapo pressure gauge that came with the can wasn't reading right, I plugged in another can of refrigerant I had and got the exact same reading on its gauge.

I depressed the pin on the Schrader valve and got a loud rush of refrigerant. So it appears that the previous owner tried to remedy the A/C issue by cranking in 100 psi worth of R134a. Yay.

I figure my next step will be to bleed the system down to a more reasonable pressure, even though any damage to the system from overpressuring has probably already been done.

Once I have done that, I am wondering what my next step should be in trying to troubleshoot the system. Thanks.
 

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do a search for reading ac codes and sensor values. i reported mine here and learned my evaporator temp. sensor had failed. $20 for a new sensor later (coulda replaced the resistor therein for $2) and my ac blew cold again!
 

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do a search for reading ac codes and sensor values.
I found this one:
W124 Diagnostic Trouble Codes (DTC) – Models with M104 Engine Only!

Pin #7 dumps the codes for the automatic climate control. What catches my eye are pulse readout #4 (Outside air temperature sensor, short-circuit) and #5 (Outside air temperature sensor, interrupt). On this car the outside air temperature on the dashboard goes in and out, and when it is showing a temperature it is clearly wrong.

So I'll see if I can scare up someone with a scan tool, or just go ahead and replace the outside temperature sensor.

Thanks for the tip.
 

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Grab a strong flashlight and see if the clutch of the compressor is engaged and spinning at engine speed.

If the face of the compressor is not spinning, compressor is not engaged.
 
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