Why a jumper wire between R and C on my old Thermostat?

[fjl128]

I just bought a Google Nest Thermostat and get ready to install. After I opened my current White Rogers thermostat, I've found the red wire is connected to C terminal instead of R terminal. Also, there is a jumper wire between R and C. I am confused because I think a jumper shall be only between R and RC or RH. As the attached photo shows, I only have W R G Y C wires. Blue wire is not connected to my thermostat. Anybody can explain why? 

I've found a similar post from last year that Nest can be wired like this without connecting C on the Nest:

White - W to W

Red - R to R (jumper not needed)

Green - G to G

Yellow - Y to Y

C - not connected

Do you think above wiring would work? Thanks!

[HVAC · Accepted solution]

Are you sure it doesn’t say Rc instead of C might be small letters behind the wire. Looks pretty straight forward swap. I would use the blue wire to connect to C on nest & on C at the furnace control board good luck. 

[fjl128]

HVAC, you're right about the RC! I only saw the letter R initially. The letter C was covered by the red wire. Yes, the jumper is indeed between RH and RC, which makes sense. Thank you!

I'd try my luck first by connecting W R G Y to Nest without C. Will create C wire connection if no luck.

[Markjosephp]

Hello everyone,

I wanted to ensure that everything was covered here.

Thanks for looking into its wiring configuration, @HVAC.

@fjl128, I hope you've found the answer you're looking for. If you're still in need of assistance with the installation and setup, feel free to let us know. Also, here are some articles that would help:

• Install your Nest Thermostat.
• How to set up your Nest Thermostat

Best regards,
Mark