"No power to Rc wire detected" E73.

[CDF1]

Doing research here this post has occurred several times but are all closed.  The answers are not fixing the problem.  This has happened daily for me for several days now.  Works fine and then error message and system turns off the AC.  My fix has been wiggle the wire a little at the connector and turn off the AC unit breaker.  It works again for a bit and then nothing.  I have used a lot of Next thermostats and this is the first of this problem.  The thermostat has been installed on a new unit since March of this year.  Nothing has changed.  Please help.

[tgdtouchton]

I know I'm late to the game here, but here's something I found while installing a couple of Nest thermostats today.  The fuse in question is for the low voltage circuit that supplies roughly 24VAC.  On my system the fuse is on a small circuit board inside the HVAC unit.  It's not installed in a normal fuse holder, it's installed using two female spade terminals.  In my situation the fuse was corrected inserted in one of the terminals but was not in the other.  It was laying on the terminal which allowed it to make an intermittent connection.  With temperature changes (this is in my attic) and vibration the connection between the fuse and the circuit board was not reliable.  If the fuse is blown you will have a constant E73 error.  There is no low voltage.  But, if you're still having intermittent issues, this is something to look into.

[KBA1]

Yes,  it was the float switch!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat

[Jude0907]

Where do I kind the float switch

[Jude0907]

Find not kind

[Nandor]

I believe you have to look up your AC model specific manual because that could be diferent in each case. It is likely accessible from outside and generally should be a part of the moisture precipitation flow out line/system. Mine is at the lower right corner of the AC (Train) where the drain line coming out and before goes to the pump which then push it outside 

[Nandor]

TRANE not Train 🙂

[Tampabay2263]

I was having the same issue. Sounds dumb but I got really pi$$ed and started hitting the float switch against the side of my unit. All of a sudden my AC started working again. I trouble shot everything mentioned here. ZERO water back up so I’m thinking the float switch itself is taking a crap. Hope this helps

[KBA1]

Yes,  it was the float switch!!!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat

[GB4]

And I'd add to that the float switch that shuts off the power to the thermostat. I had the same no power until adjusting and emptying the float switch.

[KBA1]

Yes,  it was the float switch! The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat

[KBA1]

Yes,  it was the float switch!!!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat. 

[QueenOfCars]

I have the Nest 3rd Gen eLearning and got the e73 error code. Needless to say, I was hot and bothered. 😂  This fixed my problem. It was just a matter of charging it via a USB cable just like charging a cell phone. https://support.google.com/googlenest/answer/9245516?hl=en

[KBA1]

Yes,  it was the float switch! The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat. 

[Nelson83]

I need air conditioning now….

[tate_Hebert]

Same exact problem here but I have voltage on the Rc wire. I checked it with a volt meter. I receive an error that there is no power on the Rc wire, but there is. The wire is straight and not corroded. 

[KBA1]

Yes,  it was the float switch!!!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat..

[MOB999]

same problem, I also checked it with a volt meter. Error that there is no power on the Rc wire, but there is.

???

[KBA1]

Yes,  it was the float switch!!!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat...

[KBA1]

Yes,  it was the float switch!!!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat.....

[Nandor]

Apparently, the 3rd gen Nest is a piece of garbage. It does not learn/do anything, except try to make you a HAVAC expert :). That could be useful but for that much the money really annoying. Might be you should be grateful for it. I went through all, from resetting to manual, changing the drain system to copper (so can not be clogged like cheap plastic tubes) taking Nest offline,  you name it. My original Nest from ~6 years ago worked offline without any problem and did what I set flawlessly until its battery died. That is solid proof of nothing wrong with the wires. Since then changed the battery, and requested repair/replacement reinstalled it, then after a while took the float switch out, etc. But the problem still exists. I have a Trane (2 stages cool 2 stages heat system) with a fancy and useless air filtration that zaps the bugs but does not clean the air (took out that one too). All this useless over-engineering is meant to be frequently repaired by professionals so every quarter of the year you can shell out a few hundred bucks. I will simplify the problem as much as possible and ignore/replace the nest altogether. I just can't imagine how much trouble is caused by the other google home automation systems which might be able to lock you out/or keep you locked in enforcing house arrest 🙂 

[KBA1]

Yes,  it was the float switch!  The main drain line that drains the AC from the unit to outside the house was clogged backing up water in the drain causing the float switch to activate. Once I cleaned out the drain line all is working fine and the Nest Code "E73 wiring report" cleared on my Nest 3rd Gen Learning thermostat...

[Nandor]

I fight with Nest for ~a year on and off. My AC system is a 2-stage heat 2-stage cool fancy self-detecting air cleaner, humidity sensor-controlled system.

1) Everything worked fine for ~3 years until my first 3rd gen NEST run out of battery. This means the Nest was compatible with my AC. Then got all the problems described here. 

2) steps I did: a) changed battery. b) regularly cleaned humidity sensor/switch c) sent back the unit for replacement-repair to Google. c) got the fixed unit back installed and set everything again from the beginning. d) all problems returned sooner or later. e) took out the fancy air cleaning system. f) took out some of the wires from the base. g) regularly took out the unit from the wall base and every time reset the date and all info required for operation. h) let the unit update itself then disconnect from the internet basically nothing worked. i) at the end, I wanted to replace it with a Honeywell unit, but what was recommended turned out not compatible with my AC. 

3) Then I set it on manual as a non-programmable nonlearning unit with the humidity sensor switch hanging out from its setting. https://www.google.com/search?q=how+to+put+nest+on+manual&sxsrf=AOaemvI5cd44XcutrtCluhu-wUgrO06KwA%3... 

and https://support.google.com/googlenest/answer/9209007?hl=en#set-schedule&zippy=%2Cturn-off-auto-sched... 

Since then it does what I want, when I want, and keep the temperature as long as I want for over a month now without any problems and all the time. Now I have a fancy-looking but stupid thermostat which actually works and I am its master :). I think we have to decide how much smart things we really need

[Lisaoloughlin35]

I am having this same issue tonight- all day. Works for about 10 minutes after I manually charge it or shut down and re start.

[Nandor]

Hi Lisa, the problem could be originated from multiple sources, and all the fixes I tried worked temporarily only. The extra I did at the very beginning is that changed the AC unit drain pipe (which goes to the pump) to copper instead of plastic, so it is can not be clogged. The only solution for me which is still working OK is taking it to manual. Try this (assuming you do not need a new battery);

1) once it is back "normally" eliminate its internet connection. IF Nest still has it the schedule will reset.

2) go with the set on the manual protocol (kill the schedule). Make sure to go through with all steps in the right order because if not it will be unsuccessful. Write it down, and go through it in one fluent series one after the other because sometimes the Nest "returns" without completing it fully and that in exchange reset its "schedule" in the next cycle. I actually never set any schedule on it from the beginning.

3) take out the humidity switch I just duct-taped it to the AC outside its holder, so it is can not be "flooded"

4) make sure that IF you have a fancy self-detecting Air Cleaner System it is clean or take out that one too. I keep the front (lighted sensor) piece in its place so all electrical is there, but took out the internal parts Now shows clean air at all times (use regular filters instead).

5) Once on manual and the "learning" capacity disabled should work OK as described

6) If still does not WORKS as You want it, send your Nest back to Google for a replacement unit, then set it to manual when first you reinstall it. Good luck. Mine still does what I want and when I want it :). 

Nandor

[Nandor]

Depending on your AC model, there still could be numerous choices like a problem with the nest plate itself (it did work for someone to get a new one from Google), battery or the Nest software interprets things wrongly. If you trace back on this conversation (my previous answers)  you will see that went through almost all the recommended fixes, BUT nothing worked for a longer time than putting the Nest thermostat on the full manual link copied here from above (if not working, try it on the original answer):

3) Then I set it on manual as a non-programmable nonlearning unit with the humidity sensor switch hanging out from its setting. https://www.google.com/search?q=how+to+put+nest+on+manual&sxsrf=AOaemvI5cd44XcutrtCluhu-wUgrO06KwA%3... 

and https://support.google.com/googlenest/answer/9209007?hl=en#set-schedule&zippy=%2Cturn-off-auto-sched... 

This might need to be repeated when for example power outage resets the Nest to defaults and it will try to run the AC as Google imagined 🙂 

[Hudtime]

I have checked the float. Nonissue.  I have checked the wire connection. No issue.  Still have e73.  What next?

[Lisaoloughlin35]

Sorry I can’t help. The vlogged drain was Mt problem and I flush the tubes monthly. Good luck - you may need tech assistance 

[GB4]

Agree.