Where are the ac hook up to add freon - 1992 Buick Riviera

no big is low pressure and smaller line is high pressure the following link will show how to safely add freon ---
Auto Recharge Yahoo Video Search Results DONT hook up to high side unless you have the proper a/c equipment the recharge tanks are hooked to the low side

If the system is low or has no Freon, the clutch will not engage. Hook up a pressure tester on the low pressure line valve. It should read 30 psi at 65 degrees outside temperature and 50 psi at 85 degrees outside temperature. If there is pressure, then it could be a fuse or AC relay. If there is no pressure, then add freon with some pag oil, plus a leak dye will have to be added to the system from the low pressure valve. Only add 1 16 Oz. can to not over pressurize the system. If the clutch engages, then check for a leak. I would recommend taking this job to a qualified technician, since he would have the necessary equipment to put the system at a vacuum of -30- To empty the system and check for a leak.

You will need an AC expert to diagnose this as it requires special skills and tools.

http://www.denlorstools.com/autoblog/2009/04/adding-freon-to-car-ac-gauge-readings-explained/
You need a set of A/C gauges (hooked up to high and low ports) to determine problem

My ac light is blinking, and the ac compressor clutchpulley is not engageing. Its also blowing hot air

It's very easy. You can purchase a kit at wal-mart or your local parts store. It will come with a gauge and a can of freon and oil. The system is setup to prevent you hooking up to the high port valve. A lot of people worry about this. You have 2 valves, one small and one little bigger. You want to start the engine and turn on your a/c. Hook the gauge up and see where the gauge needle goes. It's easy to read and will tell you if the system is low or overcharged. If the system is overcharged before you begin it needs to be checked out by a shop. If you need to add, screw the can onto the adapter, with the gauge still hooked up. Once you have the can on tight, screw the t-handle to pierce the can and hold can in up side down position. Make sure when yo pierce the can you screw the t-handle completely down and slowly turn it back open to let the freon in until the gauge reads full, or whatever the gauge may state. After it's full close the valve off at the t-handle and disconnect from your a/c unit.

how to add ac freone to 2006 chevy equinox

dont!!! an you start to add freon, itll start to cycle the compresor clutch until within safe operating pressure and then it will hold clutch in constant. charge liquid(with can upside down). if wont take freon in this manner than your more than low on charge. running low on charge will quickly destroy pump, especiallt those old harrisons. the refrigerant also cools the compressor. good luck and wear gloves-

All three of the above answers are incorrect. There is no need for freon to be introduced into the system, if the system is fully charged. If you do this, and follow the above advice, you will damage your AC compressor. What you need to do is get the vehicle hooked up to a set of refrigerent gauges at a local competent service center, and the pressures will tell your competant mechanic what to do next. NEVER 'add freon' if you are not 100% sure that the system is low.

What you will be looking for (in your engine compartment) looks almost like a large valve stem that you would see on a tire. It will probably have some kind of plastic cap on it.

It shouldn't be that difficult to find. You may want to search for an engine compartment diagram for your make/model/year vehicle.