The a/c quit on my 87 560SEL today. The compessor does not engage. I put gauges on it and it has plenty of freon. I checked and wiggled all the fuses. I jumped the high pressure swich at the drier and the aux fan came on. I also jumped the low switch, but still no compressor engagement. Checked for voltage at the clutch (=0 volts). I tried all button positions including defrost. What should I look at next. Please give detailed instructions including componet location. Thanks. You all have been very helpful in the past.