How do I replace my old Honeywell thermostat with a Nest?

Question

Just moved to a 1985 built house in Ontario, Canada that has a Honeywell thermostat that I'm trying to replace with a Nest. I am unable to understand the labeling of the current thermostat as the wiring diagram is partially torn so I'm not sure how to connect the Nest's corresponding wires.

Old thermostat model is Honeywell T7512A - photo attached. New thermostat is a Nest - photo attached

Questions:

1. How do I mix and match? I am unable to find this information in the thermostats manual. Are the torn labels B for Blue and Rh by any chance?
2. In the bottom row, that yellow/golden connector is a conductor - is that what they call the common wire or a jumper wire? I don't think this has any use in the Nest, right?
3. Nest says its not compatible with a 110v or 120v system, where can I check my units voltage? I saw a junction box in the furnace room with wire nuts that has 220v hand written. Is there any other clue to be sure?

EDIT:

I found where the cable is spliced under the flooring. Here is the sequence of colored wiring coming from the thermostat to the board:

1. Red wire spliced and connected to new Red wire secured to the R slot.
2. White wire spliced and connected to new Red wire secured to the W1 slot.
3. Green wire spliced and connected to new Green wire secured to the G slot.
4. Blue wire spliced and connected to new Black wire secured to the Y/Y2 slot.

Here is the furnace wiring diagram:

Here are the splices:

Answer 1

I have never done this before but with my life knowledge I'm assuming the following:

1. The colors of the cables follow a standard for which signal they carry. The torn diagram just shows what color goes where (W for white, G for green, etc), same thing with your nest (Y = yellow, G = Green, Rc = red) ... the manual should explain what to do.

2. After a quick google search, it looks like nest can automatically determine to use the jumper, so connecting the red wire to either the Rc or Rh would work.

3. 120V doesn't mean the voltage of your actual heater, it means the voltage for controlling it. Since these are tiny wires they are likely only ~24 volts (so you're safe to install)

Answer 2

According to your notes, your { red, white, green, blue } wires are connected at your furnace to { R, W1, G, Y }.

According to the documentation for your thermostat, showing the labelling that is torn from your actual one, that is what is expected:

I therefore conclude the following, pending confirmation from you that you have A/C and your old thermostat has a battery:

1. You have A/C, and your old thermostat has a battery
2. The red, white, green wires are used in the obvious and expected way. The blue wire is used as Y, the demand for cool. (Usually a yellow wire is used for that).
3. You do not have a C wire
4. You cannot easily use a Nest thermostat with this cable. You need 5 wires.
5. The advice, and photo, you got from Nest support is wrong.

If it's not too difficult, the solution is to pull a new cable with more conductors. If the thermostat is on the ground floor and you have an unfinished basement ceiling it is the best approach. Otherwise you should look for other existing Questions describing options for people without a C wire. There are LOTS of questions and answers about that.

You should closely inspect the brown cable to see if there's another conductor hidden inside. Long shot but worth a look.