Intruder - in my case pulling the aux fan leads off the sensor and shorting them together caused the fan to run - so the fan is not suspect - just control circuitry.
Arthur Dalton - Sounds logical. I'm taking my 560 out of winter storage this weekend. Outside temps here are about 35F during the day, 25F at night. If I engage the compressor with this outside temp. will I still see foam in the spyglass if I am a little low on freon? I would appreciate your input. On my car, even if outside temp is over 90F the engine would not climb to over 105C under worst conditions. If however, I put the air cond. on the temp would climb over 5-10 min.to 110C at which point I turned the air off. I now realize that by turning the air off the engine temp sensor which kicks in at 115C did not get a chance to kick in the aux fan on high. However, the freon pressure switch never turned the aux fan on low at any time. The fan was dead as the temp. rose. Temporarily, last year, I left the freon pressure sensor wires shorted together so that the aux fan was running all the time and there was no overheat - engine ran at 105C MAX with 90-100C normal on real hot days with air on. That is why the sensor became suspect. Your low freon makes sense. All I need to know to save evacuating the air cond. system and replacing the drier and sensor - is will the low freon show the frothing in the spyglass regardless of outside temp. I am ashamed to say I have never checked the spyglass - I know now I should have.
Thanks for your input. If I am low on freon, I will find out this weekend and report back.