2000 yukon xl, the fan switch only worked on 5, now its not working at all. the passenger side defrost fan was making a squealing sound. help

If front park lights are working highly unlikely headlight switch is the issue. Is the vehicle equipped with a trailer towing package and wiring to the rear? I would start there. This vehicle may also have a taillight module located under the vehicle on the passenger rear attached in the wheel well area that goes bad

well,
you can check for passenger climate control
this is in the right side, just make sure the a/c is on and temp is to the coolest...

Sounds like a bad blend door actuator. That's the motor that diverts air between the heater core and AC

Take it apart again you probably didn't lock connectors tight or pinched a wire or something silly.
Go at it again slowly you'll find it.

You may be right about the sun roof. It should have 4 tubes to drain water that comes in around the glass. Sometimes the tubes fall off letting the water come into the cabin. The horn may be the part in the wheel. Apply it at different angles and it might start working. Sometimes they get rusty. I think your cabin filter would be under the hood near the firewall on the passenger side with a plastic cover.

The door panel will have to be pryed off after all screws are removed and the motor must be replaced

if the fans are working , it seams like the compressor is not turning on, check the low pressure switch on the acomulator, at the passenger side in the engine compartment, try wiggling the connector , that switch is very common to fail in the GMs that year, another thing find an auto-part or walmart close to you and bay one of this bottles of freon with a gauge and check if there is freon in the system , if no just put some untill the compressor come on by it self and you fill the cool air inside the car..hope this help

check fuse,blower motor relay and blower resister(mounted in blower box) and blower motor

yes it does sound like that is your problem. try checking for used one.

Check underneath your dash passenger side, you might have a little slot with 2 either 7 mm or 5.5 mm screws holding a cover, behind that you may have a cabin filter which often times clogs up... hope it helps...

goodluck...