Where is the low pressure value located so i can add freon into the compressor

You can add freon without the compressor running. There is a pressure switch in the system that prevents the compressor from operating when the freon pressure is too low. Just add some freon and once the pressure increases, the AC clutch will engage.

if the charge is low the compressor will not run add Freon to low port side with engine running and A/C on. If it is a low charge problem the compressor will turn on and cycle until the low pressure is corrected.

Sounds like the fittings are reversed.
With the compressor running, the low side should drop below zero then climb to 60 or 80 psi as you add freon.
You would need to jumper the low pressure switch to engage the compressor clutch to add freon. The compressor must be running.

The low pressure service port should be located on the accumulator.

Depending on how much freon is in the system, it could be a faulty low pressure switch or a faulty clutch.
You would jumper the low pressure switch to eliminate it for a test.

The actual part is usually a pressure switch. There are 2, one for high pressure and a second for low pressure. The low pressure switch is often on the black oblong tank or closest to it.

To test the low pressure switch you can unplug it and get an insulated looped wire to place into the harness connector you removed. Then while the engine is running and the controls are set for A/C, you briefly connect the wire into the harness to bypass the part.

If the compressor clutch makes a noise and engages, remove the wire.
The compressor is on a safety lockout. You must find a Freon leak and restore the Freon to the system. Depending on whether the Freon is all gone or just low will determine your next step.

You can borrow gauges from Autozone, Advance, or Oreilys for a refundable deposit. If no Freon is present, you need to purge the system after fixing the leak. There are additional products used to find leaks.
Ask at the autoparts places. There are also leak sealers.

If you are lucky enough to be just low on Freon, adding a can of Freon with sealer may fix it. The autoparts places can tell you more about this.

The common mistake is in overfilling the system or with severe leaks, failing to add oil to the compressor. The gauges, manifold gauges as they are called, are needed for best results.

You want a moderate charge in the system. If you are off on either high or low end pressure, the switches will kill the compressor clutch. A moderate charge will keep the compressor operating more steadily.

Aside from the pressure switches, the system can have a fuse in the fuseblock. I believe your problem will be with the pressure switches and low Freon.

Get an r134a refrigerant add kit from Walmart or your local auto parts store.

You can even get a can of Arctic Freeze by Intermatics that has a hose and a gauge on it.

Connect the hose to the low side port. You can find this port on the 'thicker' piping that comes off of the compressor (versus the thinner piping that comes off the compressor which is the high pressure side).

Pressure should read 25 psi to 45 psi on the low pressure side when the compressor is running and the a/c is on.

Pressure should read 75 psi to 100 psi on a hot day when the car is off.

However, you'll want the a/c to be running when you add freon.

Press the button on the can to install more freon, if needed.

2006 Kia Sorento EX. I had this same problem. It started after I had the ac compressor replaced. At first it was intermittent, it would blow cold and then blow hot, blow cold then blow hot again until it just started blowing hot. Turned out it was the AC relay switch in the fuse box under the hood, I swap it out with the horn relay switch (they were the same type relay switch) the ac has been working fine ever since and the horn also works even with the bad relay switch. Go figure?

You have to locate the low pressure line and connector port. Trace the two lines back to the firewall that come from the compressor. You will find 1 port on each line. They are usually covered by a plastic cap of some type that unscrews. Your refill hose, assuming you have a standard refill can with attached gauge, will only attached to the low pressure side. The two ports are slightly different in size. The low pressure side should be the larger of the two lines you are tracing from the compressor.

Check your fuse for the A/C. If it is okay then you need to locate the low pressure cutout switch and temporarily put a jumper in the connector. If the clutch kicks in, then you need to check the Freon pressure on the oblong black tank or hose directly adjacent to this tank.

Do not run the compressor very long with the bypass.connected or the compressor can burn up. However the compressor must turn to build pressure from the remaining Freon.

If you are lucky the Freon will only need to be topped off. This means the Low pressure switch did its job of preventing damage. Add Freon with a Sealer and you may close the leak that let out the Freon. Some of the gauges are not expensive, and some cans have a one-time use gauge on them.

The low pressure switch can also get weak and shut your system off early. Its a screw off-screw on part and easy to replace. Then if your compressor is noisy after working on this you may need an oil charge. That would mean you had a substantial leak and you lost the lubricant for the compressor. But you may be lucky and get by just by adding Freon.

I wanted to be informative in case the easy steps do not work for you so you can try several things. Good Luck on your repair.