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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Honeywell T874R Thermostat with One Setpoint Lever.

Customer Question

I have a Honeywell T874R Thermostat with
One Setpoint Lever. I am wondering if it has the correct wiring to upgrade it to a more modern WiFi one. I was looking specifically at the Honeywell RTH6500WF.
The last time I replaced a thermostat (in a different home), it was one that required batteries, so power wasn't an issue.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Uploading a couple pictures of the unit w/o the cover
Customer: replied 1 year ago.
Expert:  gotoman for ac replied 1 year ago.

Looking at front of thermostat. You have an Emergency heat light. You should have a common wire on thermostat. So you will be fine with the 6500. Remove front of thermostat and let me know if you have common or C wire.. Russ

Customer: replied 1 year ago.
Nothing labeled a C, so I'm guessing the namong convention changed at some point.
Customer: replied 1 year ago.
Found this old diagram online
Expert:  gotoman for ac replied 1 year ago.

Wire new thermostats this way.

Red to R

Orange to O

Yellow to Y

Green to G

Blue to C

White to AUX/W2