How o you recharge ac regrigerant

It all depends, has the AC system been recharged?
If it has and it's not blowing cold air it could be that the AC compressor is ceased. If the AC recharge has been done by you, did you make sure that there was no pressure in the system with an ac compressor vacuum? If the AC Compressor had some pressure left in it and it was recharged without first vacuuming the system, that can cause it to lock. Another possible issue is that it has a small leak somewhere.

Melvin, Recharging a cars A/C system. Check the attached links,instruction and guides, Good luck
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How to Properly Recharge Your AC System

besides replacing the compressor you have to change the accumulator/ drier and recharge with the correct gas
AS this requires specialist knowledge it will be best if you have an accredited ac specialist shop do the job

You should have R134a, you can tell by the quick connect ports that you use to fill your AC system. the 134a use larger ports that have 2 different sizes, one of the caps will be about 5/8 of an inch in diameter and the other will be about 1/2 on in diameter. If you still have the old R12 system you will have both caps about 3/8 of an inch in diameter.

There is a high pressure side and a low pressure side on your refirgirant line the fittings are different sizes because it is very dangerous if you hook up to the wrong side of the line. Make sure you read the directions on the recharge kit and follow them precisely. The high pressure side fitting should have a red cap and the low pressure side should have a blue cap. You will need to hook the charge kit to the LOW pressure side to recharge.

You need to add some refrigerant (R134). Whats happening is that since it is low on regrigerant the compressor sucks the low side below the cutt off pressure turning off the compressor, then pressure at the low side builds up again quickly and turns the compressor on again then sucks it back down again untill it turns off and the cycel goes on and on untill you add enough regrigerant in there. Here are some caution do not overcharge the system. Overcharging will make it not get cold properly and will damage the compressor costing you a lot more money. The low side should reach a minimum of 35 psi with the AC blower on maximum. This keeps the compressor on all the time. If say you were to put the blower on minimum the evaporator would get really cold since the air passing through it is less. This would cause the low side pressure to dip down gradually until the compressor cuts off, and that is how the system basically works

Purchase 1 more can and allow it enough time to fully get into the system. You can have the car running while this is happening so it warms the can allowing it to charge faster. Let me know.

1. Make sure the vehicle is off with key removed.
2. You need to evacuate the refrigerant with a refrigerant recovery system.
3. Remove the ribbed belt.
4. Remove the noise insulation beneath the engine.
5. Remove the bolts (1) from A/C compressor and disconnect refrigerant lines.
6. Remove hex screws (2) and remove the compressor.

Reinstall in reverse order making sure the bushings (3) are seated. Make sure your new compressor is filled with regrigerant oil prior to install and you do not start the car prior to filling it back up with regrigerant. Turn the ribbed belt pulley of A/C compressor 10 rotations by hand before starting the engine.

Assuming you do not have a leak preventing a recharge, here are some basic steps on recharging:
http://www.aa1car.com/library/ac_recharging.htm

R134a can be purchased at any auto parts store..

Your AC is low on refrigerant; The AC compressor needs a minimum amount of regrigerant to run. If and when it does run (while low on refrigerant) the air coming out of the vents will not be cold. The refrigerant you require is R-134A and is available over the counter but if you are the least bit unsure as to how to add refrigerant, taking it to a garage that does AC recharging would be your best play. If you want to try to add refrigerant on your own you will need the following, 1LB can of R-134A, an AC hose adapter to deliver the refrigerant, and preferably an AC pressure guage to ensure you are not overfilling the AC line which will damage the system.