Nest E Thermostat & Taco Zone Controller (zvc404)
#1
07-13-18, 10:57 AM
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Nest E Thermostat & Taco Zone Controller (zvc404)
I am hoping for some HELP from experts as the Nest support stinks.
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.
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.
#2
07-13-18, 11:23 PM
Group Moderator
That zone controller was not designed or intended to run power stealing thermostats. The nest requires a certain amount of current flow which is not present in most zone controllers. I would only connect wifi thermostats to it using three wires which would include a C connection.
If you have three wires between the stat and the controller..... I can help you.
If you only have two wires you are pretty much out of luck,
If you have three wires between the stat and the controller..... I can help you.
If you only have two wires you are pretty much out of luck,
#3
07-14-18, 06:10 AM
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That would be unfortunate. NEST's compatibility checker claims a C wire is not required. The first NEST E that I have had for 6 months has worked fine using 4 wires without a common with this current set up. I am not sure what is different about this zone 2. Could it be how it is wired to the air handler and AC condenser?
#4
07-14-18, 07:42 AM
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Thank you so much for the help. I think I might have found the problem.
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?
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?
#5
07-14-18, 09:22 AM
Group Moderator
I missed the presence of A/C. When using the nest with A/C and heat...... the A/C powers the nest.... not the heating system.
There should be a Rc, G, and Y connection between the A/C and the stat. The current flow thru Y and Rc is what keeps the stat charged. There needs to be two additional wires that connect from Rh and W1 to the zone controller. The two heating wires will not connect to any of the A/C wires.
If you have a spare wire to the air handler.... you could add a C connection for maximum reliability.
There should be a Rc, G, and Y connection between the A/C and the stat. The current flow thru Y and Rc is what keeps the stat charged. There needs to be two additional wires that connect from Rh and W1 to the zone controller. The two heating wires will not connect to any of the A/C wires.
If you have a spare wire to the air handler.... you could add a C connection for maximum reliability.
#6
07-14-18, 10:55 AM
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Thanks!
Here is a diagram of the wiring from the AC Air Handler to the original Honeywell thermostat (attached). The only direct connection from the terminal in the air handler to the thermostat is the terminal Y to the thermostat R. The thermostat G and Y are attached to white jump wires (I think) in the air handler that I believe go to the mass of wires in the left side of the attached photo (which is up in real life but the photo was rotated. I also attached a photo of the air handler terminal (also rotated left).
I am not sure how power gets to the thermostat since there is no R connection from the air handler to the thermostat. There is no specific Rc and Rh slot on the NEST E, just an R. From your response, am I correct in saying that connecting a C wire would help? I have both a light blue and a brown wire that go from the air handler to the thermostat which are not used. Would connecting one of them to the C terminal on the air handler and to the C slot on the NEST E help?
Here is a diagram of the wiring from the AC Air Handler to the original Honeywell thermostat (attached). The only direct connection from the terminal in the air handler to the thermostat is the terminal Y to the thermostat R. The thermostat G and Y are attached to white jump wires (I think) in the air handler that I believe go to the mass of wires in the left side of the attached photo (which is up in real life but the photo was rotated. I also attached a photo of the air handler terminal (also rotated left).
I am not sure how power gets to the thermostat since there is no R connection from the air handler to the thermostat. There is no specific Rc and Rh slot on the NEST E, just an R. From your response, am I correct in saying that connecting a C wire would help? I have both a light blue and a brown wire that go from the air handler to the thermostat which are not used. Would connecting one of them to the C terminal on the air handler and to the C slot on the NEST E help?
#7
07-14-18, 12:31 PM
Group Moderator
Water trap wire ??? I'm not understanding your diagram.
There should not be any wire from Rc to Y.
The nest E is a stripped down version of the nest. I'd need to check and see if it can handle separate heat and A/C. The regular nests do.
There should not be any wire from Rc to Y.
The nest E is a stripped down version of the nest. I'd need to check and see if it can handle separate heat and A/C. The regular nests do.
#8
07-14-18, 01:56 PM
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I appreciate the help and apologize for the lack of knowledge on my end.
Here are two new pictures.
The first is the diagram again with the colors of the wires labelled. In the original and currently functioning wiring of the Honeywell thermostat, the red colored wire goes from the Y terminal on the air handler to the Rc. This can be seen on the sideways shot of the air handler terminal as well. The white wire goes from the white terminal on the thermostat to this "Water Trap Wire" (see below) not touching the air handler terminal at all but is connected by a wire nut. The green and yellow wires go from their respected terminals on the thermostat to wire nuts (skipping the terminal in the air handler) and form the wire nuts into the air handler (either into that mass or wires on the left or to the Zettler 24V black cubes in the air handler.
There is no wire of any color going from the air handler R terminal to the thermostat.
The next picture is of the white "Water Trap Wire" that leaves the air handler and is wired to a white rectangular bobber that must close a circuit when water collects in the black drip pan to the extent that the bobber floats.
The last two pictures are of the old Honeywell and new Nest E wiring. The NEST E only has one R terminal, not separate Rc and Rh slots like the NEST.
Here are two new pictures.
The first is the diagram again with the colors of the wires labelled. In the original and currently functioning wiring of the Honeywell thermostat, the red colored wire goes from the Y terminal on the air handler to the Rc. This can be seen on the sideways shot of the air handler terminal as well. The white wire goes from the white terminal on the thermostat to this "Water Trap Wire" (see below) not touching the air handler terminal at all but is connected by a wire nut. The green and yellow wires go from their respected terminals on the thermostat to wire nuts (skipping the terminal in the air handler) and form the wire nuts into the air handler (either into that mass or wires on the left or to the Zettler 24V black cubes in the air handler.
There is no wire of any color going from the air handler R terminal to the thermostat.
The next picture is of the white "Water Trap Wire" that leaves the air handler and is wired to a white rectangular bobber that must close a circuit when water collects in the black drip pan to the extent that the bobber floats.
The last two pictures are of the old Honeywell and new Nest E wiring. The NEST E only has one R terminal, not separate Rc and Rh slots like the NEST.
#9
07-15-18, 11:35 AM
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Well, looks like the NEST might have defeated me.
I attached the C wire and the NEST still gives an error for the red wire. It looks like it needs the red wire to be powered. There is over 20V between the red and the green, the red and the yellow wires, the red and the white, but just about 4V between the common and the red. There is no V between the other wires and the common.
I looked to see how the zone 1 thermostat is wired to the zone 1 air handler. It is wired normally with the correct colored wires to the correct location on the air handler terminal. I am not sure why the zone 2 air handler is so messed up.
Unless there are other thoughts, I am returning the NEST.
I attached the C wire and the NEST still gives an error for the red wire. It looks like it needs the red wire to be powered. There is over 20V between the red and the green, the red and the yellow wires, the red and the white, but just about 4V between the common and the red. There is no V between the other wires and the common.
I looked to see how the zone 1 thermostat is wired to the zone 1 air handler. It is wired normally with the correct colored wires to the correct location on the air handler terminal. I am not sure why the zone 2 air handler is so messed up.
Unless there are other thoughts, I am returning the NEST.
#10
07-15-18, 12:08 PM
Group Moderator
The Nest E is not designed for two systems. It will not work with two distinct 24vac sources.
The other nests would work fine here.
The nest E has caused more problems then it's worth.
The other nests would work fine here.
The nest E has caused more problems then it's worth.
