A/C fuse burning 85 spider

[Irtimed@domain.elided]

2 weekends ago I degreased the engine in my 1985 Spider veloce and 
subsequently drove it without incident.  I did notice, however, a clicking 
noise in my fuse box which may or may not have been related to the a/c 
operation.  When I opened the box, there was sparking in the #7 and #8 fuse 
(it actually burned through the upper plastic ledge).  I changed the fuses 
and it hasn't done it since.  My main concern is that every time I turn on 
the air conditioning, the 20 amp fuse in the engine compartment mounted on 
the wheel well sparks and burns.  I looked at the  compressor and the ground 
wire is attached to a nut and the oil pan.  My questions are:  
1)  What is causing the 20 amp fuse to burn as soon as the a/c is turned on?  
 
2)  Has anyone had sparking of the #7 & #8 fuses (the connections behind the 
fuse box look good) and what can cause this?
Your comments and insight will be greatly appreciated  :)

Thank you in advance,
Demitri
irtimed@domain.elided
1985 Spider veloce
Omaha, Nebraska

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