Weak A/C on an early NA is often the system doing its best with the wrong refrigerant: 1990-1992 US cars came with R12, and converting them to R134a loses cooling capacity because the condenser was sized for R12. From 1993 the factory switched to R134a and added a condenser cooling fan to compensate. Know which system you have before you diagnose.
If your early car cools poorly, work through it in order.
- Confirm the refrigerant and charge. An R12 system that has been topped up over the years may be a mystery blend. A proper evacuate-and-recharge to the correct weight fixes a lot of "weak A/C."
- Retrofit correctly, not just fittings. A real R12-to-R134a conversion means new O-rings, a fresh receiver/drier, the right refrigerant oil, R134a service fittings, and ideally the correct orifice. Bolting on adapter fittings and dumping in R134a gives you the disappointing results people complain about.
- Add airflow. Because the early condenser is undersized for R134a, a clean condenser and a good pusher/condenser fan make a real difference. This is exactly what Mazda did for 1993.
- Verify basics: compressor engaging, condenser fins clean and not bent, and the cooling fan actually spinning when the compressor is on.
On any car, correct charge is everything. Overcharging hurts cooling as much as undercharging. If you cannot get cold air with a verified correct charge and an engaging compressor, move on to the condenser, expansion device, or a restricted drier.