Q: Air conditioning is pretty much useless

The A/C indicator light blinking is an indication that the system is low on refrigerant or a defective pressure sensor or wiring issue. The way you described your problem is that it is an intermittent one. The fact that your system works fine at times tells me that most likely your system is not low on refrigerant but instead a sensor or your wiring is the issue. The system has a pressure sensor mounted to the A/C compressor which senses the pressure in the system and if defective could cause the erratic signal causing low pressure indication when the system is not low on refrigerant. I recommend you contact YourMechanic to have a thorough A/C diagnostic test and computer scan for A/C codes. The technician will confirm A/C pressures are normal and electrical wiring is not damaged to the A/C pressure switch. They will then scan the computer and check for A/C codes and diagnose as needed to give you a repair solution to fix your problem.