That unit will have it's own circuit protection. You may need to follow the power wire to locate the fuse. Back in the day when I put these kind of units in I always went to the start solenoid and put the fuse on the battery side of the solenoid and then ran the circuits to the relay so the unit would shut down when the key was turned off. As it was converted to 134 you may need a better low pressure switch as it maybe set too high for the lower 134 pressures. Plus your system may have developed a leak just due to the 134 as it has smaller molecules and if you had any weakness in any seals it will find them and start leaking. And I do hope they put in the right compressor oil for your unit as some of these older compressors did not do well with PAG oil and needed ESTER oil. Good luck.