This should serve as a guide to removing and replacing the heater core in a 1971-1974 Fullsize Buick including, Electra, LeSabre, Centurion, Riviera and Estate Wagon. There will be minor differences between the years, but the basics are the same. This write-up was done on a 1971 Buick Electra 225 Limited with air conditioning and automatic climate control. 1. Disconnect negative battery cable 8mm wrench (or 5/16) 2. Remove Fire Extinguisher (If applicable), remove contents of glovebox, remove floormat. 3. Use a #1 Philips Screwdriver to remove the (5 ) screws holding the liner to the dash assembly. There are three at the base of the liner and one on each side. Shown below are four of the (5) screws removed.