Warning light says Low Refrigerent-AC/Off. I tried to recharge the system but the Compressor won't engage, How do I get the Compressor to come on so as I can recharge the system. Is it a pressure swithch problem or has the Computer shut the system down. Thanks.

That's a sign that your system is very low of refrigerant. So it's best to find and fix the leak before refilling. Adding refrigerant on a system that's low and leaking is a really bad idea. See these two posts about how to diagnose a compressor clutch that won't engage and how to recharge http://ricksfreeautorepairadvice.com/ac-compressor-clutch-not-engaging/
http://ricksfreeautorepairadvice.com/ac-recharge-on-your-car-or-truck

Woody have refrigerant level checked may be low. have a good shop recharge A/C system if checked and found low. Check the attached links,instruction and guides, Good luck
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FIXED Car Compressor Clutch Won Engage
The Trainer 40 When the compressor won compress
Diagnosing AC Compressor Clutch Problems

first thing check AC compressor fuse.the AC compressor clutch should engage when you turn on airconditioner if AC compressor dont come on and fuse okay compressor clutch is open or low on refrigerant you need check your AC refrigerant low pressure side and high pressure side need a manifold gauge set. best let garage check out AC system could need system recharged or could have leak in the system.

The refrigerant may be low or empty. The compressor may be bad. You will need to have a mechanic check it out.

What gas was used to recharge the system?, if compressor does not engage, then the compressor clutch is broken, needs to be replaced.
I hope your son didnt recharge the system with Freon, most cars now are filled with R-22.

If system is low on freon, it will not kick in, may be a good place to start.

the most common cause of course is a low system refrigerent charge, this would be due to a leak, the most common cause of leakage is the front shaft seal of the AC compressor

Have you checked the refrigerant level,If it is low,No power will be supplied to the compressor.

Change your compressor it has got damaged.

Charging the A/C system is really simple. I have a '98, but don't know why a '97 would be much differrent. So, see if this works for you.

You will need a charging hose with a guage and two or three cans of refrigerent (R-134A). If your system is out of refrigerent you have a leak. So, make sure one of the cans you buy has marking dye in it so you can figure out where the leak is. Depending on how large a leak you have, it may take several weeks and months or just a few days. Most canned refrigerents have a sealing material that may plug the leak for an extended period of time or even permanently.

With the engine running and air conditioning on, disconnect the harness from the low pressure switch on the accumulator (left side of engine compartment).

Use a small wire to jump acoss the two contacts, the compressor clutch should engage and the compressor should start turning.

With the refrigerent can attached to the low side hose (blue connector), connect the hose to the low side port on the accumulator.

Open the valve on the charging hose. Refrigerent should start flowing. Shake can periodically refrigerent is drawn into system. Can will feel very cold and probably begin sweating as the refrigerent evaporates and is drawn into the accumulator.

There should be technical sticker under the hood to tell you how much refrigerent to charge system with. When it reaches the correct pressure 25 to 45 psi depending on ambient temperature, you are close to the correct charge, (most gauges you get at auto parts stores have a "blue zone" to indicate proper charge) close charging valve and disconnect the hose from accumulator. Though you can't tell exactly how much refrigerent you've put in, by knowing how much is in each can and how many cans you put in you will have a pretty good idea.

This will all go fine as long as you don't have a bad compressor or other sealed system problem.

Good Luck!