One lever on each side is heat on that side, so if you have all levers in the down position, all heat should be off.

The water valve for the heater is vacuum controlled. It needs vacuum to keep the valve closed. So if you have a bad valve. or a vacuum leak somewhere, it will go to full heat. One way to fix this itemporarily is to locate the valve and vacuum line on the firewall. Disconnect and plug the vacuum line and then you can manually move the valve to the closed position, which should cut off the heat.

The permanent fix is to find out where the vacuum is being lost. It is fairly common for the diaphragm on the valve to go bad.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe