What would cause the clutch on the a/c pulley to slip and not completely engage?

Your response caused me to recheck everything and check everything I hadn't thought of. A/C pressure with system off is 120PSI low side and 125PSI high side (85*F). As you know the A/C clutch & pulley can only be seen from a side view and there is no way to see the face of the clutch. With the engine cool I reached down and felt around the face of the clutch and realized that two of the three clutch pins and bushings where gone. The clutch is shot. Luckily I did get the A/C clutch to engage and produce cold air. A/C pressure with the system on was 40PSI low side and 195PSI high side (85*F). Thanks

You may want to consider replacing JUST the clutch field coil, pulley w/bearing and clutch disc if the compressor isn't growling and seems to be ok otherwise... In ANY event the cooling fans must turn on very shortly after compressor is turned on.. If they don't.. this will happen again!

Thanks. I think that will be the repair.

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Check reply to "Pushrod". In this situation slipping means that the clutch might catch and turn a half rotation or a quarter rotation then stop. As it turns out I checked the clutch face and found that two of the three pins and bushing where missing. Thanks

Glad you got it! Thanks for bothering to reply , most don't! Enjoy!