What does it mean if the thermostat nest has no power to RC Wire? Ways to fix it

So one day, an error appears on your thermostat, and Nest has no power to RC wire. Also, along with this, there may be an E73 error on Nest.

Thermostat ​​Nest is an electronic thermostat with a wireless connection and programming function. Its main function is to optimize the operation of domestic heating systems. It has a learning function, i.e., in the first few weeks, the user sets the temperature manually, and then the thermostat adjusts the temperature according to their preferences. The thermostat is wired to the A/C system. Actually, it is the so-called control panel for the conditioning system. Like any other device, the Nest thermostat can fail without proper maintenance. Next, we will analyze the causes of malfunctions and the reasons why such errors as no power to the thermostat appear. Also, we will offer quick troubleshooting Nest thermostat steps.

Possible causes of this error

So, one day you discover that the A/C system is not working. You approach the Nest control panel and see that it indicates the error “no power to RC wire” detected with a link to nest.com e73. Here are the possible causes of this error:

• Lack of electricity in the house.
• Incorrect thermostat model.
• Wrong wire connection.
• The A/C switches may have been turned off by mistake while the system was running.
• Broken wire contacts on the control unit.
• Perhaps due to power outages or the A/C system’s work, a short circuit in the wires and the fuse blew.
• The drain system is too dirty with mold or dust.
• Voltage drop in the A/C system.

How to fix the issue of the Nest Thermostat having no power to RC wire?

Since the causes of the error when there is no power to the thermostat are different, the elimination of these malfunctions is also different and can be associated with different methods.

If you have the opportunity, then contact the company or person who has installed the thermostat or the entire A/C system for you, but be prepared that the service or troubleshooting may cost money. On the other hand, if your system has been installed recently, it could still be under warranty.

If you have installed your system yourself or want to try fixing this issue with your own efforts, follow the instructions below.

Attention! This manual assumes that you have experience with electrical systems. If you read the instructions and you did not understand much, it is better to contact a specialist.

What is RC wire?

The RC wire is the physical wire that is connected to the back of the Nest thermostat and is usually red in color. Voltage flows through the wire from the air conditioner to the thermostat. The Nest has batteries, so when there is no power on the Nest thermostat, this way, the control panel detects a malfunction of the A/C unit.

Check the RC wire connection

Before proceeding with the instructions, read them and prepare some tools like a multimeter, screwdriver, and side cutters.

To check the connection of the RC wire, follow the steps:

• Please, shut down the power to your A/C system by turning off the switch. Your system may have multiple switches, or you may turn off the switch in the electrical panel. If you do not know where the air conditioning switch is located in the electrical panel, contact a specialist.
• Remove the thermostat display from the wall mount. While holding the thermostat ring, gently turn it towards you opposite the wall.
• Press the latch on the RC wire to disconnect it.
• Press the latch with the * symbol and disconnect the usually black wire. If you do not have a connected wire at this position, disconnect the other wire at position C or Y1.
• Examine the exposed RC wire and black wire. They must not be corroded or polluted, broken or bent. Strip the RC wire and other wires if necessary.
• Connect the multimeter to the RC wire as plus and minus to the other wire. Use a multimeter to check for short circuits in the wires. Double check none of the wires are touching each other.
• Turn on the power.
• The voltage on the voltmeter display. It should be a 24V alternating current. If there is no voltage, the RC wire is broken somewhere on its length or in the air conditioning unit. If the voltage is lower, this may mean that the air conditioning unit is faulty.

• Turn off the power.
• Return the RC wire and the other wire to your contact points. Check that the wires are held tight.
• Return the Nest thermostat panel onto the wall mount.
• Turn on the power and wait until the thermostat is turned on. Check what it indicates.

If the E73 Error on Nest persists, go to the next guide.

Check the fuse on your A/C system

Your A/C system has a fuse that protects the system from various failures. And when it fails, then everything goes go wrong. It could be power fluctuations, short circuits of wires, malfunctions of the air system, or overheating of various elements of the air conditioning system. Especially in very hot weather, this fuse works most of the time, saving your system from serious damage. A broken fuse also leads to the Nest E73 error.

Follow the steps below to inspect or replace a fuse:

• Turn off the power A/C system. Make sure the power is off and the fans are off.
• Locate the control unit of your cooling system and remove the protective cover.
• Find the fuse on the board. It will be similar to the fuse used in cars. Usually, they are rated at 3A.

• Inspect this fuse for signs of blackening or burning. Just pull it out of the board and check if it is burned out. Check the fuse with a multimeter.
• If the fuse is broken, take it with you to the store and buy another one.
• Insert a new good fuse back into its position.
• Close the protective cover.
• Turn on the power to the A/C system.
• Look for the E73 Nest error on display.

If the E73 Error on Nest persists, go to the following guide.

Check the A/C filter

For stable operation, the A/C system must have good airflow. If the filter is clogged or dirty, then the air does not enter it as smoothly as it should. As a result, your system may break. Please refer to your system manufacturer's instructions for filter operating times and maintenance schedules to keep your A/C system running smoothly. Failure to follow this rule can also lead to error E73 on Nest.

To replace the filter, follow these guidelines:

1. Find an air filter for your A/C system. If you don't know where it is located in your system, check your A/C system manual or contact a specialist.
2. When you find the filter, inspect it for dust and dirt in its holes.
3. If the filter looks clogged, turn off the power on the A/C system. Then take it out and put in a new one.
4. Turn on the A/C system and check its operation.

If the E73 Error on Nest reappears, continue to the next guide.

Check the drain pipes and coolingcoils of your A/C system

During the operation of the A/C system, the drain pipes become clogged with debris, which leads to the pump’s shutdown. The system shuts down too and causes the “Nest thermostat no power” error. To fix this issue, follow these steps.

• Turn off the A/C system.
• Find the drain line for your A/C system. The drain line can be found in different places, depending on where your air conditioner is located, for example, in the attic or the back room.
• Locate the overflow switch. The condensate overflow switch may be located near the A/C system’s air handling unit or the condensate drain’s outlet. There is a little low-voltage cable leading to the controller that you can identify.

• Remove the switch, then check and clean it. After that, lift the condensate overflow switch and remove it from the PVC pipe, then wipe thoroughly with a tissue or cloth. If necessary, you can add a few drops of soap to the water. The overflow switch for the condensate line should have a small float at the base that can be easily moved up and down. If it doesn't work easily, then you need to call a specialist and replace the switch.

• Check the drain pipe for dirt or debris that could clog the drain line.
• If the pipe is dirty, clean it with a pipe cleaner. Then pour a glass of cleaning agent to remove the scale from the water.
• Flush the pipe with pure water and check if the water flows evenly. If the water does not flow evenly, then the drain pipe may be damaged or very clogged at the bottom. In this case, call a specialist.

• After cleaning the drain pipe, turn on the A/C system.

How to charge the Nest thermostat accumulators

Suppose you come home and find that your Nest thermostat is not powered. There is no indication on it, and when touched, it does not react. Probably the batteries in the thermostat are dead. Also, if there were no power for a long time through the RC wire, then with time, the thermostat would turn off due to a dead battery. After the power supply is restored via the RC cable, the battery will charge itself. But you can also charge it via USB charging. Follow these steps to charge your thermostat:

1. Take off the thermostat from the wall. While holding the thermostat ring, gently turn it towards you away from the wall.
2. On the back of the thermostat, you will see a USB connector. Connect it to the charger as you charge your smartphone. After a few hours, the batteries will be fully charged.
3. Slide the Nest thermostat panel back onto the wall mount.

If in the process of performing one of the guides you need help, it is better to contact the specialists.