My left front wheel squeeks until i press the break pedal

Usually a sign one of the front brake rotors is out of round. It could also be something wrong with the abs but I doubt it.

There must be air in the system some where. i am not sure of the year ,make and model of this van and also not sure of the brake system, for example if you have drum brakes in the rear then first adjust them.
The next step is to fill the master cylinder, make sure there are no leak anywhere.Next step start at the master cylinder, at the line to master do not worry about abs system. have someone inside ready to pump brake pedal and hold.Have them pump pedal three times and hold pedal with a little pressure.make sure as you open the bleeder they push on pedal and keep foot on brake until you tell them to pump again. the pedal is to be pumped three times every times.
With pedal pumped start at master lines, open one allow to bleed a little then close and move to next and allow to bleed. if master has more than two lines then pump again and do two, open one and close then open two and close then pump again. After master is bleed a few times and no air comes out then move to right rear wheel, pump three times and hold while you open bleeder, this is to be done about four times to make sure you get a good flow of fluid with no air .
NOTE: always keep master cylinder full, check after each wheel. make sure the person pumping the brakes does not lift until you say and the bleeder is closed. After the right rear wheel you will move to left rear and then right front wheel and last is the left front wheel.
Make sure there are no bad wheel bearings, lift wheel of the ground and grab and check for movement by pulling wheel out and in from top to bottom, the last thing is make sure the caliper slides are free moving.
If the caliper does not slide on the bracket freely then the piston will not stay on pad and pedal will need to be pumped to get a pedal. good day.

Sound like you either have air in the system or a leak. Make sure all the connections are tight on the new calipers. clean off all the connections and blessed screws with brake cleaner. Then have your partner press on the brake pedal while you look for leaks. Reblead the entire system again starting at the right rear, than the left rear, than the right front, and finally the left front. Continue bleeding at each wheel until no air comes out. make sure you don,t let the master cylinder go dry. It will take several pedal pumps for the caliper pistons to take up the gap in between the pads and rotors. I assume you have a helper pushing on the brake pedal during the bedding process?

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

you need two persons
open the bleeder screw on the wheel that is furthest from the master cylinder and do the nearest last.
have a person pump on the brake pedal and hold firm while you open the screw, then close it before tell the person pump again
repeat until you see no more air come out
make sure you fill up the master cylinder, do not let it run out of fluid

do you mean that you pump the brakes to build up pressure in order to stop?

bleeding brakes requires you to bleed them from each wheel starting at the right rear. procede as follows: have someone sit in the drivers seat. have them pump the brakes slowly and forceably to build up pressure. maintain force on the pedal. starting at the right rear, open the bleed screw slowly. the pedal will go to the floor and the fluid will drain. hold the pedal to the floor and tighten the bleed screw. repeat this procedure several times until you are sure there is no air in the line. follow these steps at each wheel- left rear, right front, left front. keep reservoir filled with fluid. fill after each wheel. (note) get a length of rubber hose that fits snuggly over the end of the bleed screw
and drain fluid into a container.

i think you were draining the anti-lock brake system. in which, case follow the steps above for that also.

You will need two people, one to pump the pedal and one to open bleeders at the wheels. Start at the right rear wheel open bleeder and have someone press the brake pedal down and hold it (do not release pedal until bleeder is closed), close the bleeder and repeat until no air is coming out. Proceed to right rear wheel repeat above prceedure, proceed to right front wheel repeat above, go to left front wheel repeat above, and then check pedal for proper feel if it is a solid pedal with no fade then you have finished. If you have a low pedal or fade then bleed master cylinder. You can bleed master by breaking loose the rear line (do not loosen line all the way) just enough that fluid comes out when pedal is pressed and held. Have some press the pedal while line is loose and hold it, tighten line and repeat until no air comes out, repeat same proceedure with the front line. If you still have a low pedal or fade then you may have a leak somewhere or a faulty master cylinder.

Because of the ABS system if you press the brake pedal with too much pressure then it will give you the illusion of a soft pedal. Does it feel like a soft pedal when the vehical is in motion and you then press on the brake pedal (normal)? The other thing is if your pads and/or caliper were frozen, when you changed them out. The brakes are not going to feel or brake exactly the same, after the repair. But you are there, if the pedal is real low or goes to the floor then there is still air in the system or for some reason, your master cylinder is defective.

If the squeeking is happening over bumps, and is not related to breaking, it could be a bearing in the steering linkage. My tahoe is doing the same thing, and my local garage says it is only a dealer fix. That is why I am searching this site now, is to find out if anyone else is complaining about this. I was told that GM is fully aware of this problem.

to do a complete job. you need to bleed all 4 wheels, starting from Right Rear. Right front. Left Rear. Left Front.

possibly belt is slipping old and worn out