Compressor Duty Cycle

[David]

What is considered a reasonable compressor duty cycle for a R12 system that has been converted to R134a? On one of my converted cars the compressor stays one for about 12-15 seconds then is off for 10-12 seconds, darn near a 50/50 duty cycle. It WAS low on R134a, it used to come on for only a second or two then click off then back on. The low pressure side is reading about 25lbs when the compressor kicks in and the vent temps are an even 40*F with the fan on #3 out of 4 with the car parked in bridge sun and an ambient temp of roughtly 60*F. I guess what I'm really looking for is confirmation on whether the system is still under-charged...

Dave
1987 CGT Special Build 2.3
SE Virginia