Cooling more than needed

[South159]

I need to verify that my nest gen 3 thermostat wiring is correct because I chanegd twonest gen 3 thermostat and I still have the same problem. When cooling, the thermostate always displays about 4 degrees higher termperature than what the room termperature really is. Therefore, the AC units ends running longer and making the rrom a lot colder. Once the unit stops, then the thermostat display the accurate room termperature, which lower than what it displays when the unit is cooling. I have a carrier high efficiency furnace model carrier model 58UVB100. My current thermostat wring is:

1. Yellow wire is connected to Y1.

2. Green wire is connected to G.

3. Red wire is connected to Rc.

4. White wire is connected to W1.

5. Blue wire is connected to *.

[alejandom]

Hi @South159,

Your wiring seems mostly correct based on the information you provided:

• Cooling (Y): Yellow wire to Y1 connects the thermostat's cooling signal to the furnace's air conditioner contactor.
• Fan (G): Green wire to G controls the furnace fan.
• Power (Rc & W): Red wire to Rc likely provides constant power to the thermostat, and the White wire to W1 seems to be your heating element control (although this can vary depending on the system).

However, the Blue wire connected to * might be causing the issue. Here's why:

• The Nest Gen 3 typically uses the W terminal for the second stage heating.* Since you mentioned a Carrier high-efficiency furnace (model 58UVB100), it likely only has single-stage heating. Having a wire connected to W might be confusing the Nest thermostat.*

Here's what you can try:

1. Disconnect the Blue wire from the * terminal. Cap off the bare end of the blue wire with a wire nut to prevent electrical shorts.

2. Test your system. Turn on your air conditioning and see if the temperature reading on the Nest becomes more accurate during cooling cycles. If it does, this indicates the blue wire was causing the issue.

Additional Considerations:

• Nest Thermostat Settings: Double-check your Nest settings to ensure it's configured for a single-stage heating system.
• Consult Carrier Manual: Refer to the manual for your Carrier furnace (model 58UVB100) to verify the functionality of the blue wire and if it should be connected at all in your setup.

If disconnecting the blue wire doesn't resolve the issue:

• There might be a different problem with your Nest thermostat or the air conditioning system itself.
• Consider contacting a qualified HVAC technician to diagnose the issue further.

By following these steps, you should be able to identify if the blue wire connection was causing the inaccurate temperature reading during cooling cycles. Remember, it's important to be cautious when dealing with electrical wiring. If you're not comfortable working with electrical connections, consult a qualified electrician for assistance.

Regards,

Mario.