How to fix AC on Mitsubishi eclipse?

@alexalejo first you want to determine where the screeching is coming from. It is possible, that once you turn the AC on and the compressor kicks in, your belt tensioner or any other pulley that has a bad bearing, screeches. You will have to replace the part that does the screeching. If it comes from the AC compressor, then it is most likely time to either change the clutch on the compressor or change the complete compressor.

"Noises that develop during A/C operation can often be misleading. For example: what sounds like a failed front bearing or connecting rod, may be caused by loose bolts, nuts, mounting brackets, or a loose clutch assembly. Verify accessory drive belt tension (power steering or generator).

Improper accessory drive belt tension can cause a misleading noise when the compressor is engaged and little or no noise when the compressor is disengaged.

Drive belts are speed-sensitive. That is, at different engine speeds, and depending upon belt tension, belts can develop unusual noises that are often mistaken for mechanical problems within the compressor.

ADJUSTMENT

1. Select a quiet area for testing. Duplicate conditions as much as possible. Switch compressor on and off several times to clearly identify compressor noise. To duplicate high ambient conditions’(high head pressure), restrict air flow through condenser. Install manifold gauge set to.make sure discharge pressure doesn’t exceed 2,070 kPa (300 psi).

2. Tighten all compressor mounting bolts, clutch mounting bolt, and compressor drive belt. Check to assure clutch coil is tight (no rotation or wobble).

3. Check refrigerant hoses for rubbing or interference that can cause unusual noises.

4. Check refrigerant charge.

5. Recheck compressor noise as in Step 1.

6. If noise still exists, loosen compressor mounting bolts and retorque. Repeat Step 1.

7. If noise continues, replace compressor and repeat Step 1.

Here is HVAC part of the SM for your vehicle. See what you find Eclipse HVAC