Nest – No Power to RH or RC wire detected

Quick little article on my findings.  So, last week, my Nest Thermostat starting acting up.  It would shut down and the screen would go black.  The AC would not crank up and it was hot in my house.

I know this in not IT or Security related, but is technology related and thought and hoped it would help someone.

When I looked at the screen, it would give me that infamous “no power to RH (or RC) wire detected”.

I swapped the RC with the RH will the same results.  ADT had installed it for me as part of my upgraded alarm system so I called them to service it.  After scheduling and waiting for them to arrive, the guy called me and told me that they do not handle wiring but rather ONLY the Nest Thermostat itself.  I was back to square 1.

• I called Nest support and although the lady was very nice, no go on the Nest Thermostat. They did offer to replace it if it was a bad unit even though I have had it for years.
• I swapped the RH and RC cables as I stated above which did nothing.
• I tried to remove the Nest Thermostat and charge it with a Micro USB cable.  The air would turn on for a few minutes then shut off.
• Purchased a new Nest Thermostat and installed it (used the same base plate though).  The issue continued so I returned it.

I then realized that my AC has a shutoff valve (see below).  The purpose of this valve is the following:  If the water starts to fill on the bottom tube (horizontal), it will raise a floater (inside the vertical tube) and once that occurs, contact is made and the shut off valve engages.  This function kills power to the…… you guessed it RC or RH wire.

Turns out there was nothing wrong with my wiring inside the house, there was nothing wrong with the thermostat and “nothing” wrong with my AC.  However, the drain line was massively clogged.  Thankfully, we have set it up in a way that I can close a valve (so no water backs up into the AC unit itself) and connect a standard garden hose and flush the line myself saving me anywhere from $150.00 to $300.00 of the AC guy coming out to do so.  Once I did the flush, the AC has been humming along.

Hope this helps someone and is able to save you money