1988 300E M103 75K miles

I recently replaced all the O rings, receiver-drier, expansion valve and added R134 and the proper amount of R134 compatable oil. My high and low side pressures were good and I was getting 40F at the vents on an 80F day. All was well until today, compressor clutch stopped engaging and when I tried to jump it (via the pressure switch) nothing. Can I send power directly to the compressor to see if it will engage? The connection has three wires to it.