Suburban Furnace SF24 fixed - FYI

Corroded or loose 12vdc connections, including grounds at the furnace , or anywhere else in the furnace power circuit can reduce actual voltage to the furnace. Connections to the thermostat can be poor too. On an old rig, spade automotive type connectors and ground screw connections can be slightly corroded lowering voltage to furnace, and solenoid valves, etc. may be balky. Cleaning circuit board connections is always good. Removing, checking and replacing fuses and tightening fuse block screws can "fix" low voltage problems. Amazing that furnaces work properly with all the lockout/safety features.