I have a 93 Del Sol S (no power steering) that the AC has started acting up at idle. Sometimes the compressor clutch cycles on and off every few seconds when idling. It happens when the engine has been reving and drops quickly to idle, such as pulling up to a stop sign or light. The idle will run up and down between 500 and 1000rpm as theclutch engages/disengages. Eventually the clutch will remain engaged and the idle will stabilize at 700rpm. The system works fine at higher revs. The clutch cycling appears to be due to low pressure.
I've had the car for about a year, AC has worked great. The sight glass is clear except a few bubbles when the AC is first turned on. I hooked up gauges and pressures are normal according to the FSM (1500rpm/ 275psi hi / 30psi low/ 95F outside / 54F vent ). Most of the time at idle the clutch doesn't cycle (700rpm /220 hi /41 low / 60F vent). There appears to be an ample charge of R12 in the system.
When the clutch starts kicking in and out the lowside pressure will drop quickly down to