Could be your refrigerant level is low.
The following simple test is in the 1984 Maintenance Manual section 8312, and is typical of all cars with AC systems.
- Start engine and run at idle speed.
- Depress button switch "DEF" [This will engage the compressor.]
- Check fluid level as follows: Pull off one electrical lead on low-pressure switch [Either of the insulated spade terminals.], electromagnetic clutch should then switch-off and refrigerant should flow back into the receiver-dehydrator.
- Reattach electric lead, electromagnetic clutch should now switch-on again and refrigerant should flow free of bubbles past the sight glass.
- In the event of foam or bubbles, there is not enough refrigerant in the system.
The receiver-dryer sight glass is located in the engine room just behind the LH headlight assembly, and the low pressure switch with two insulated spade terminals is right next to it.