Screeching sound On right side. Around the belt. Replaced idler bearing, tension bearing, and alternator. Belt is new. Still makes the screeching sound when I press on the gas.

The screeching is the belt slipping, two possibilities, either the belt is not tight enough, or you have fitted a faulty pump which is putting to much resistance on the belt? If it carries on screeching for any length of time it will break. Check your alternator belt tension, if you had to remove and refit that? Quick check for alternator belt is, switch on headlights, does the screech get louder? Don't over tighten the belts, this puts stress on bearings!

A couple of things come to mind: if it wasn't screeching before replacing the belt, you may not have routed the belt properly - especially around the belt tensioner pulley; or the bearing on that pulley may need lubrication or replacement; or the A/C compressor bearing may have failed causing excessive resistance on the new belt resulting in screeching. Also, if the belt was not routed properly, the screeching may be coming from another belt-driven (power steering pump, water pump, etc.) but it doesn't sow up until you engage the A/C with its additional drag.

Probably one of the other belts. A bearing wouldn't just screech for 30 seconds. Could also be the power steering pump low on fluid.

Did you replace the belt tensioner

The pulleys may be out of alignment due to a bent or misinstalled alternator bracket. the alternator itself may be pulling so much current that the belt is slipping on its pulley. (might be why the other alternator failed. Check the battery voltage with everything turned off and see if you have a parasitic battery drain.) The bearing for the idler pulley (if equipped) could be failing.

When the AC compressor kicks on, an electrical load is placed on the alternator and the drive belt that turns the alternator pulley, if not tight enough, can cause the belt to squeal. Replacing the belt should help with that noise if the belt is stretched from wear. The screeching noise can be from a bad idler pulley, a bad belt tensioner pulley or a bad alternator pulley or a failing clutch on a very old ac compressor and rarely a water pump pulley. To check pulleys remove the drive belt and turn them individually to see if they can be tilted up down or sideways with play in the "bearing" of the pulley. Also, you may wish to visually inspect the clutch on the ac and look for melted black rubber around the bolts that secure the clutch to the compressor (stinks,smokes and melts these rubber areas if ac compressor clutch fails).

Alternator bearings a possible. Idler Pulleys or Belt Tensioner Pulley

Sounds like your drive belt is slipping, it is either worn out or needs adjusting. You may near it louder when turn your steering wheel.

sounds like idler bearings but you have to release the tension to check,Also you can check the rest of the pulleys also at this time. I dont think you have to drop the engine.

If the belt is not tense enough it will squeal, so make sure it's tight enough. Otherwise you can use a stethoscope or long screwdriver up to your ear to isolate the source of the noise.