A/C makes very loud humming sound

Check air filter and catalytic converter and muffler for good flow

humming could be the motor turning round but not engaging with the flywheel. you can check this by hitting the starter with a spanner a few times. if it starts up after you have a sticking solenoid. had to do this a few times my self to get engine started. replace starter as soon as possible if it works. usually happens if you not driven car for awhile.. or you do a lot of starting and small trips.

sounds like something is draining the battery while parked. was the replacement battery new? get it checked for faults, can happen.. buy a cheap amp meter with a blade fuse probe. remove each fuse one by one and look for high current values while car turned off. this should then give you an idea of what in the car is draining battery, refer to manual for items on fuses. dash lights take very little current to light but to turn the engine takes loads, hence no spark

check to see if the battery is good..all connections are snug..there is power loss somewhere..if alarm is activated some will still beep others will chirp.. turn lights on and try to start the car..if lights go dead..battery is too weak to be any good..if new..put on charger..look at the charger guage.. 6 amp charger will show pegged needle when first plugged in if battery is good, then drop back to normal rate until full takes a few hours..check all connections..good luck..

Sounds like a wheel bearing .

Alignment will not create a sound by it's self. The most common cause of humming (especially if you have an agressive tread design)is a wear pattern in the tires...check for that or rotate the tires around & see if the noise changes. If it does then you know it's in the tires. & Not always, but most of the time a bearing noise will increase or decrease in intensity if you load up one side at a time by doing 35-50 mph & turning slightly to each side.

Could be either a loose belt or you are low on power steering fluid,or the power steering pump could just be worn out.

yes your right... it could be the wheel bearings, try replacing them.

Did you replace the alternator with a new or used alternator? The transmission is controlled by the alternator on pacifica's. Check your caytilatic converter for the humming noise..

Did you remove battery cables while charging? Rmove and make sure grd is clean and tight Turn on the ignition, watch gauge. It should reset itself. If not, start engine and drive around the block. then make sure you park on level ground , then shut off the engine. Did that work? If not, disconnect the battery for a few minutes and hook it back up. Last but not leastm go put gas in your tank. It just might be full. Pranks have been known to happen. Good Luck.