<VV> A/C Question - Help!

[Bill H.]

                                                                               B"H
Hi guys, I hooked up my A/C system, got the belt on the compressor, adjusted all the brackets, and verfied the wiring.   Looked OK, so I turned on the system, and good news, the clutch engaged and the compressor started working.
First problem, the person who had the system converted to R134a put the same fittings (low pressure) for BOTH sides, despite one red and one blue plastic cap. 
I purged the high pressure side side with my equipment, then charged the system with some oil. seemed OK. Then I connected a can of refrigerant, and...
BOOM!!!!!
A huge spark, acrid smoke...I know I've done something wrong.  I disconnected my gauge set, then looked again at the compressor.  Started the engine, compressor seems to work fine despite the incident.
Now I'm wondering if I connected the Freon to the wrong (high side) by mistake??  Does anyone know which is the low side port and which is the high side?  Which side is the one with the muffler attached to the refrigerant line?
Thanks again...Bill Hershkowitz  66 Monza Sport Sedan 110 PG A/C