I'm having trouble getting my MendelMax 2's heatbed not to heat up when I want to print without it. I don't get how multiple sources of control relate to each other (same with extrusion temperatures, actually):
Slic3r (1.2.9) has settings under Filament Settings / Filament / Bed, for First layer and Other layers (and groups of settings can be saved).
The pronterface GUI (Printrun-Mac-10Mar2014) has an "Options" panel where you can set "Bed temperature" (actually, two settings, one for PLA and one for ABS -- though I doubt the software can test which filament is loaded!)
The pronterface GUI also has a menu/fill-in labelled "Bed", which works fine to adjust the bed when nothing is printing. The menu there lets you pick from a manually-entered value, "0 (off)", and (apparently) the settings for PLA and ABS from the options panel.
Marlin's Configuration.h has settings for bed minimum and maximum temps (the non-zero minimum seems to be to prevent running the bed when the thermistor isn't working, to avoid unlimited overheating).
I recently tried to print some PLA with no bed heat (using blue tape on the glass build plate). I sliced the model with bed heat off in Slic3r; changed the PLA bed temps in the printerface options panel to 0; and picked the PLA setting in the GUI main screen (and also tried setting "0 (off)" manually.
When I started to print the object, the bed turned on and stayed on, maintaining 60C.
I thought of just unplugging the heatbed, but then I expect the print would never start, since it would try to heat up the bed and never succeed.
So how does the decision about which temperature setting to use, really get made? I have the same question about extruder temps, speeds, accelerations, and other things, too -- whose settings are really in charge?
3D printer get the temperature settings from g-code file. The firmware settings for min and max temperature are just safeguards.
Instruction responsible for setting bed temperature are M190 and M140. Open your g-code file and search for lines containing them. If you delete these lines then the bed temperature will be not set during print. Additionally it means that it is set by your slicer.
In Slic3r you should check Printer settings → Custom G-code → Start G-code if it contains one of mentioned instructions and possibly remove it.