I started my 84 Honda Civic with dealer installed air when the car was new. As I pulled out to go home the A/C exploded with a bang, a cloud of vapor and moisture around the edges of the hood and then nothing. Upon inspection the sight glass had blown off. The A/C had been opened up to get the compressor out of the way for maintenance on the engine and the original R-12 Freon was put back in. Any ideas?