Nest E Thermostat Error E195

nesthelp

I am hoping for some HELP from experts as the Nest support was unable to help.

I just purchased and tried to install a second Nest E thermostat and only get an e195 error (no power to the R wire). I have a gas furnace and AC system with 4 wires (no c wire) and the furnace has a Taco Zone Controller (zvc404) with three thermostats and a water heater. The zone 1 thermostat is the first Nest E which has worked fine for 6 months. The new one is in zone 2. The water heater is zone 4.



What I have tried:
1. The new Nest E works fine if installed in zone 1 (the first Nest E location).
2. The old Nest E thermostat from zone 1 also does not work in zone 2 if installed there (even if the zone 1 thermostat is disconnected when trying zone 2).
3. My old Honeywell thermostat works fine in zone 2.
4. The fuse in the Taco zone Controller seems fine.
5. I get the same reading on a volt meter between the red and white wires at the thermostat for both the zone 1 Nest E and the zone 2 Nest E. It seems to be between 20-30.
6. I get the same reading on a volt meter between the red and white wires at the Taco zone Controller in zone 1 and zone 2.

I cannot understand why the Nest E will not work and the Nest support offered no suggestions. Any help would be greatly appreciated.

Jamie Hall

A couple of thoughts, mostly off the top of my head -- since I have never installed a Nest and hopefully never will.

Keep in mind that the Nest needs to have power. In your setup, with only the two wires feeding it and no independent power or return, it's not the happiest camper, but it will usually work.

So. First thing I'd look at is the voltage between the TT terminals on Zones 1 and 2 with the Nests connected. You should read somewhere around 24 volts. Then have both Nests call for heat; you should read close to 0 volts. You can put your old Honeywell back on and try it, too; you should get the same results.

If that's OK, are you sure -- really absolutely positively sure -- that the R wire for thermostat 2 is reading 24 volts to common -- not the white wire -- both at the controller and at the thermostat? If that result is ambiguous, or if you have no access to common at the thermostat, try switching the white and red wires at either the controller or the thermostat. It is possible that somewhere in the wiring the red and white got crossed; it would make no difference to the old Honeywell, which is a nice simple switch, but it would make all the difference to the Nest.

nesthelp

Thank you so much for the help.

I have measured the voltage at the different wires in the thermostat. From red to white 28; from red to yellow 22; from red to green 28. I have no common wire to measure to at the thermostat.

I then traced the brown cord with 6 wires (yellow, red, white, green, and two unused ones - brown and light blue) which goes into the wall from the zone 2 thermostat. I followed this brown wire back into the wall with a camera and it goes to the air handler before going to the furnace.

The air handler is a Freedom Air AHXWY800A1. I traced the individual wires from the thermostat to where they connect to the air handler and they seem screwy to me.
Red -> Yellow slot in air handler terminal
Yellow -> a wire cap to a wire that goes into air handler
White -> a wire cap which connects it to the water trap shut off wire
Green -> a wire cap to a wire that goes into air handler
Light Blue -> not used
Brown -> not used

The air handler terminal has a C (common slot). It sends wires out of the air handler to the water trap shut off wire and another thermostat multiple wire.

I am guessing that because the wires are mixed up at the air handler to the thermostat that is why I am having issues?

Jamie Hall

"I am guessing that because the wires are mixed up at the air handler to the thermostat that is why I am having issues? "

Most likely... but you may have a bit of a time between the various controls and units on figuring out which wire really should go where -- and I'm not about to second guess over the internet!