Thanks for all your concerns! My A/C's better now. Here's what I did:

DISCLAIMER: Although I was supervised by a certified mechanic, I'm not a mechanic in any shape or form, so follow the information below at your own risk. If you can, just get your car to the shop. I did this, since I have time, and someone looking over my shoulders. :)

  1. Rented A/C Manifold Gauge Set from Autozone (Free, just put a refundable deposit).
  2. Rented 2.5 CFM A/C Vacuum Pump from Autozone (Free, just put a refundable deposit).
  3. Bought a gram scale from Harbor Freight.
  4. Bought 2 cans of R134a without additives.
  5. Looked at the A/C's capacity under the hood of the car; mine's 500g.
  6. Evacuated the system, but hooking up the A/C Manifold Gauge Set to the system, and the A/C Vacuum Pump to the manifold.
  7. Checked for leaks, but turning off the vacuum pump, close the manifold valves, and waited for 10 minutes.
  8. STOP HERE IF THERE'S A LEAK. THE FOLLOWING INSTRUCTIONS BELOW WILL BE USELESS IF THE AC's LEAKING.
  9. If the low-side gauge needled didn't move for 10 minutes, it's a good assumption that there's no leak.
  10. Vacuum the car for more that 30 minutes. I didn't do this, but some folks in the Internet vacuumed it for 24-hours to make sure moisture's out the system.
  11. Close high and low valves of the A/C Manifold Gauge Set.
  12. Weigh the can with the R134a Can Tap Valve-Screw-On in grams.
  13. Screw the R134a Can Tap Valve-Screw-On to the yellow line of the A/C Manifold Gauge Set.
  14. Release the valve of the R134a Can Tap Valve-Screw-On to release the refrigerant to the manifold set.
  15. At this point, there's no refrigerant going to the car's A/C system yet.
  16. To make sure there's no moisture and air on the manifold set, release a little bit of refrigerant by loosening the end of the yellow line in the manifold set. It's the end that's attached to the manifold gauge. As soon as a little bit of gas gets released, close it back.
  17. Boil water in a pot.
  18. Turn on car's engine, and set the AC to LO. At this point, ECON might be lit up. The reason is that the car detected that there's no refrigerant in the system, and turned off the compressor to avoid damage.
  19. Open the LOW side of the manifold gauge, releasing refrigerant to the system.
  20. Slowly submerge the R134a can to the pot with boiling water. This will help the refrigerant go in the system. I found out that this is needed in the car since the compressor is turned off. I think there's a way to short circuit the compressor to force it to engage, but I didn't go with that route.
  21. While trying to fill the system with refrigerant, also look at the low side gauge and make sure the needle's turning clockwise. Note, sometimes the needle will drop. This is normal, the refrigerant traveled to the car's A/C system and the pressure eased. As long as the general direction of the needle is clockwise (increasing), this means that refrigerant is entering the system. You can also feel the metal fitting near the Can tap valve, and it should be cold.
  22. If the can's very light, close the low-side valve AND the R134a Can Tap Valve-Screw-On.
  23. Remove the yellow line from the R134a Can Tap Valve-Screw-On; leaving the R134a Can Tap Valve-Screw-On on the can.
  24. Weigh the can and the R134a Can Tap Valve-Screw-On on the gram scale.
  25. Do this math. Original weight - Final weight - 57 grams
  26. 57 grams is 2oz that is wasted by releasing a little bit of air and gas that is in the manifold gauge hoses. I found this value in the Internet.
  27. EX: 716g - 409g - 57g = 250g
  28. Since my car needs 500g, I need 250g more.
  29. I added another can of R134a, and did the process again starting from weighing the R134a can with the R134a Can Tap Valve-Screw-On.
  30. The value that you're trying to hit is 500g. Since we're dealing with crude tools. We can miss plus/minus 50g, it's noted in the hood of the car.
  31. This means that for 500g capacity, you should not exceed two R134a cans. Those cans are rated 356g.
  32. FINISH:
  33. TIP 1:You might need to turn the ignition on and off in the middle of filling up the 2nd can. This helped me engaged the compressor, and turning off the ECON LED.
  34. TIP 2: Your air coming from the A/C vent should start cooling in the middle of the 2nd can fill. NO TEMPERATURE CHANGE SHOULD HAPPEN ON THE FIRST FILL, COMPRESSOR IS STILL TURNED OFF.
  35. TIP 3: You might find out that refrigerant is not entering the system. Please double check the line fitting, and make sure it's working properly. For me, I discovered that the manifold gauge set that I rented is defective.
  36. TIP 4: Make sure that the low side and high side ports are connected to the manifold fittings well. Mine had a leak, and discovered it when I tried to vacuum, and turn off the vacuum pump for 10 minutes. I thought my A/C system had a leak, it was just the fittings to the high and low side ports.