[shorod]

Does the compressor clutch still engage? If so, it sounds like you may have the not uncommon Dual Coolant Control Valve (DCCV) problem. If the DCCV fails to shut off the flow of coolant to the heater cores, you'll get way more heat than the evaporator core can overcome.

You could also try resetting the climate control unit to see if that makes a difference, but chances are pretty good the DCCV is the issue. The procedure to reset the climate control unit has been posted here before, so I won't repost but instead point you to the very useful "Search this forum" feature from the Lincoln LS forum main page.

-Rod