89 560SL If the outside temperature is mild the a/c works ok.  Not
super cold, but ok.  If it sits in the sun (Phoenix AZ 110 degrees)
the a/c may or may not come on.  Yesterday I noted it did come on.
After 10-20 seconds the aux fan started and then after less than a
minute the whole system shut down.  No a/c, no blower fans, the aux
fan stopped and the only way I could get anything was to press
defrost.  Than makes the fans blow , but the compressor does not run.
After a few minutes it tried to run again and shutdown in less than 30
seconds.  I have tried shorting the two switches near the sight
glass.  Nothing changed.  This morning the outside temp was mild.  The
system started up then died after 20-30 seconds.  As I was driving to
work it suddenly came back on and worked the rest of the time (12-15
minute commute) blowing cold but not really cold even though the temp
dial was set to the lowest temperature.  This is an R12 original
system.  Has new mono valve.  Belt seems tight.  May have some bubbles
in sight glass. (hard to tell)  Have not had opportunity to put guages
on it.  But I think the compressor would have to be running to tell
anything, correct?