When I turn on my AC I csn see the AC compressor pulley engage for a few seconds then disengage. Then it catches again and disengages. Any idea why that would happen?

 

Because it's low of refrigerant, which has all leaked out.

The low-pressure cutoff switch, when the pressure in the low side of the system goes below about 20 psi or so, breaks the circuit supplying power to the clutch, to prevent damage to the system.

Find and repair the leaks and refill the system. Consider retrofitting to R-134A.

 

Ah makes sense. any tips for tracking down the leak?

This probably also explains why my secondary coolant fan never kicks on

 

Look for refrigerant oil around all the parts of the system.

If you see it on the underside of the hood above the AC clutch, the compressor front seal leaks. (very common) If you see it at the end of a rubber hose section, the rubber hose is bad; it's seeping into the hose material and coming out the end. (inevitable, haven't seen one yet that didn't)

Usual best policy is, don't even bother "tracking down" leaks. You have them, and there's a bunch. Everywhere. Always are. Best thing to do is, replace the compressor, accumulator/dryer, orifice tube, EVERY O-ring, and EVERY rubber hose. Pressure test the condenser and evaporator and replace if they leak, otherwise flush them and the metal lines with NON-RESIDUE solvent such as lacquer thinner, MEK, acetone, or denatured alcohol, or {GASP!!!} the right thing, AC flush - NOT mineral spirits, brake cleaner, or degreaser, using compressed air to blow it through. Might want to consider popping the top off the evap housing and removing the evap, and washing it off... you'll find that it is INCREDIBLY gross and disgusting, always is. Check the lower half of the housing and make sure it isn't crumbling to dust right where it's closest to the exh manifold; usually is, repair with fiberglass patch from the inside if it is, being careful not to build it up to where the evap wont fit back in. Put the housing back together using windshield sealer around all the joints. Add about 3 oz of PAG oil to the suction port of the new compressor and about 2 oz to the accumulator; re-assemble the system using PAG oil on the O-rings; draw it down to a vacuum and keep the pump on for about an hour to boil off any moisture or leftover solvent, then shut the valves and turn off the pump, and see if it holds vacuum; if it loses less than 1" of vacuum in a half hour, add a can of R-134A, turn the system on, and add 2 more cans. If it doesn't hold vacuum, find and repair the leak, check again, and repeat until it does. Use the Frod orange orifice tube rather than the GM one. Ask for the one for a 96 Crown Vic, it happens to be more suited to a GM R-12 system filled with 134A (mismatch) than the GM one is.

 

Wow thanks for the extremely thorough write up. i know next to nothing about the AC systems in these cars so it is clear i will need to do some reading. it's not high on my list as i prefer not to use the AC but just like knowing everything works.