Check the blue plug on the temp sensor. If someone shorted it, then the fan will come on full speed when you switch on the ignition and the A/C compressor will not engage.

Remove the plug and check the resistance across the pins.

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold