As with most vehicles today, the Navigator has a serpentine belt. This is a long piece of rubber. Rubber stretches over time. When serpentine belts stretch, they get loose on the pulleys. Of course, the squeal you hear could be a bearing going.
Lincoln is havn`t timing belt,there only chain :-)
On a 2005 Lincoln Navigator : It has ( 1 ) timing CHAIN to each cylinder head , so there are ( 2 ) timing CHAINS
On a 2005 Lincoln Navigator ( no ) There is ( 1 ) timing CHAIN to each cylinder head , so it has ( 2 timing CHAINS )
Check the belt on the ac compressor of the 2004 Navigator. It sounds like the belt is slipping when the ac first comes on.
On a 2000 Lincoln Navigator there is a timing CHAIN to each cylinder head ( two timing CHAINS ) and a serpentine belt that drives all the engine powered accesories ( air conditioning , power steering , etcetera )
Your belt is correctly tensioned?
chains
Most likely it is a belt on your car. Usually the squeeling is from a loose belt while idling and will also make noises while driving.
you might have to bleed your system it sound like you air in it
Tighten it.
The belt is probably glazed. Clean all the pulleys and replace the belt. Do not use a belt conditioner on a serpentine style belt.
2004 Lincoln town car belt diagram