Classic/Antique Car Repair: a/c blower problems, compressor cycles, question number

Question
#1 my a/c blower works only on medium speed , will not work on low or high speed. #2  compressor cycles on an off but  Cycles to 10psi before cutting out rising to 60psi before starting again ,is this normal. 1978 corvette factory a/c.

Answer
Question #2 is probably due to low refrigerant level in the system. The clutch should cycle to control A/C temperature but the low side pressure should not drop to 10 PSI. Question number one deal with the possibilities of a defective blower resistor, bad switch, or bad wiring. It is time to get on with a voltmeter and wiring diagram.
Brad