first make sure the sytem is properly charged , a low charge and the compressor will not stay engaged , you could be overcharged and hitting the overpressure limiter in the compressor
the adjustment is on the clutch cycle switch on the dryer , for r12 it may turn off at 24-28psi , for r134 conversions you could have the switch run lower
you have to remove the rubber electrical plug and theres a screw inbetween the terminals but you really need to have a gauge connected and know what your low side cycles down to ,
be aware that 134 should be filled to around 75-80% of what the r12 capicity was.
originally was 3.25 pounds R12, with r134 thats about 3.5 12 oz cans and the retrokits dont include enough for us