i went to the cafe today ready for some paint prep work but instead i spent the whole day helping my father reroute some wires for the nest thermostat. the cafe has a roof-mounted air conditioner for cooling and a basement gas furnace for heating. first step was figuring out a key to decipher how the wires from the AC and the furnace connect into the existing thermostats. and i say thermostats because even though the wires go through two thermostats, only one of them actually worked. though the AC unit is new, the HVAC installers never ran a common wire since the previous thermostat didn't need it. however, the nest thermostat does require a common to have enough electricity to run the background when neither the AC or furnace are on.
i already checked, and the old furnace in the basement doesn't have a common connector. however, i was pretty confident that the AC on the roof would have a common, so we climbed up to check. luckily even though they didn't run a common wire, they still pulled a 6 wire cable and were just using 3 of them, so we could use one of the spare wires to be the common.
opening the AC control panel, i was happy to see there was a spot on the board for a common wire. however, the rest of the wiring confused me. downstairs, the previous thermostat only used 3 wires, but in the control panel 4 wires were connected. even more mysterious, the wire for the Y call (grey) wasn't connected to the Y call spot on the board, but instead spliced to some other wire that disappears further inside the AC. the wire used for the Y call on the thermostat (white) was connected to the W call on the AC board. also the R call was jumped to something called the OCC which i'd never seen before. confusing wire notwithstanding, it seemed to work so i left everything as is after connecting the common wire (orange).
i rode the motorcycle to belmont around 1:40pm to look for some equipment, including a box of wiring nuts and a drilling spade. when i returned to the cafe we took a break so i could have some lunch. i brought my torx screw along with my father's fired TYT radio so he could open it up and see what was fried inside. there were a few suspicious spots, but everything everthing looked normal, no major damage. we could've also checked the other side of the circuit board but the amount of screws needed to be removed made it too much of a hassle.
back on the thermostat installation, we secured the wall mounting plate and drilled a 1-1/2" diameter hole into the sheet rock wall. since the existing wires from the AC and furnace were too short to reach the other side of the doorway (where we wanted to mount the nest), we had to pull new wires. we used a length of ethernet cable. all we had to do was snake the wire from the doorway up into the ceiling, a distance of about 2 yards, but that seemed to be the hardest thing we had to do. we tried it from bottom to top, then top to bottom, but finally managed to snake it successfully going from bottom to top. i spliced together the heating/cooling wires with the ethernet cable using wiring nuts.
i popped in the nest thermostat but nothing happened, it remained dark. maybe we made a wiring mistake, or maybe the battery in the termostat was dead. the nest has a usb port (for debugging purposes) so i connected it to a usb charger. it lit up with the familiar nest logo, so at the very least the thermostat was okay.
putting the woke nest back on the wall mount, it was able to go through the initial setup, but when it ran the wiring diagnostics, it said there was no Rc or Rh wires. that made no sense, so i tried to fix it by disconnecting wires. first, all the AC wires (Y, G, Rc), but that didn't do anything, it still said something was wrong, this time just the Rh since it couldn't see Rc. could it be the common wire? i disconnected the common and put started the nest, and this time it didn't give me any errors. i reconnected all the AC wires as well, the AC worked fine too. so the common wire was the culprit. but without a common, how can the thermostat charge itself? but the nest seemed to be very happy without a common, never once complained. we even saw it was recharging itself, so it was definitely getting power from somewhere, we just don't know where. we decided to left everything as is for the time being.
i finally left the cafe by 5:20pm, my parents were about to close up shop anyway. i went home and took a shower. doing all that ceiling work, some bits of ceiling panel fell into my hair. while shampooing, some debris fell into my eye. i tried washing it out but it was no use. it actually got me a little panicked and i was seriously thinking about going to the emergency room to see if they could dislodge the debris. it took the rest of the evening before it finally cleared, after i kept washing my eye intermittently in the bathroom sink.