An ABS fault.
Pin cone
bearning on front breaks burn out
No , ABS is the anti-lock brake system
Since the first model year of the Mercury Mountaineer is the 1997 model it would be ( r134a )
Check the main crank pulley.
rings or seals
Bearing in: Alternator? Water pump? A/C Compressor? Belt tensioner?
Look for a hole in the PCV valve hose on the backside of the engine.
That would be the 4.6 liter engine, which takes six quarts. * of 5W-20 according to the 2003 Mercury Mountaineer Owner Guide
Vacuum leak in a/c door control system . Look for vacuum leak under the hood.
Check into the ABS pump or module ---- I would say the pump