I have read Do I have one or two 24V transformers in HVAC control circuit, but as it appears I don't have two geographically separate units for A/C and heating, believe this to be a different question.
However I also bought the Nest E for installation, and hence need to know if this one transformer thermostat will work with my system.
Can you please take a look at the below images and let me know if this will be as simple as getting both cables to the same location (haven't discussed with my other half whether this new thermostat will be up, or downstairs) and hooking up control wires as the instructions state, using the wire attached to the R terminal in the thermostat set for heating for R, and cap the wire attached to the Rc terminal in the thermostat set for cooling (or vice versa)?
Below is where the cabling from each thermostat, and to each of the gas furnace and unit outside for electric cooling, cables converge: (The cable with the red wire wrapped around it goes to the outside box with a fan in it; the condenser? The other cables go up through inaccessible wall cavities to each thermostat, but without a continuity tester that can be used to test one wire going to different locations, assume that the cable with the blue and green wire wrapped around it at the back of this bundle is the one that goes to the heating thermostat, with the other to the cooling thermostat).
The gas furnace is below a box with pipes coming from the outside cooling unit go into.