Trying to install this thermostat in place of the old one that was there.
I turned off the breaker at the panel, got all the wires correct. The old thermostat had a jumper wire between RH and RC that I didn’t carry over as per the instructions. Put all the wires in and flipped the breaker back on - and nothing. Tried it all again a few times - nothing. Don’t have my meter on my to check the red wire power but the breaker isn’t tripped or anything.
By “nothing” do you mean that the thermostat is not powering up? Or that it is powered but not turning on the HVAC when expected? I’m guessing you mean it is not powering up, correct?
So that we can best assist, please post a photo of the thermostat wiring.
Thanks, looks fine unless there is a short from broken sheathing somewhere I can’t see, which would be pretty rare.
I’m guessing it was a standard 24VAC system, but just to confirm can you verify the model of the old thermostat?
It was a pro T701 which online says it’s 24v
Without a meter to test the power, we’ll need to check another way. If you reinstall the old thermostat, does it power on without batteries? It is important to test without any batteries.
If not, check wiring at HVAC to ensure C-wire is connected. It is possible the old thermostat was just running on battery power.
So before installing I checked the old thermostat without batteries and it remained on. I needed to do this to find which breaker controlled the thermostat because most aren’t labelled. The first breaker I tried turned off the thermostat power so I assumed I got lucky. I then did the install and didn’t get electrocuted or anything so assume that was in fact the correct breaker.
When I didn’t get power to the new thermostat I did re-connect the old one with just the red wire and blue wire, with no additional jumper. It did not power on when I turned the breaker back on. I didn’t try it with the jumper also, assuming the two wires alone would at least give it signs of power.
When I didn’t get power to the new thermostat I did re-connect the old one with just the red wire and blue wire, with no additional jumper. It did not power on when I turned the breaker back on. I didn’t try it with the jumper also, assuming the two wires alone would at least give it signs of power.
This is important. If you have already tested and reinstalled the old thermostat, and it too is now not receiving power, that means that the issue is indeed the power source. It should power on with the R and C wires connected to the R and C terminals, which I think is how you tested, correct?
You might try again with the jumper just to be 100%
It is possible that there is a blown fuse within the HVAC system. If any wiring changes had been made while there was power on the circuit or if there were any wiring shorts at some point when power was applied then this is likely.
Sometimes there will be power switches on or near the HVAC system as well, just in case it is relevant.
I would triple check the main power panel and make sure all of the breakers are in the on position. I know you mentioned doing this but it would be best case cause.
If power is successfully delivered to the HVAC system but the thermostats are not receiving 24VAC, that suggests an internal fuse is blown or damage to the wiring. You can visually inspect the wiring, but may need an HVAC tech to diagnose if the problem is internal.
All the fuses inside the hvac are good. Breakers are all on. No voltage coming from the red wire.
Actually scratch that, I think I’m getting 28v ac from the red wire.
Aaaand I solved it.
I had the yellow wire going into Y and the blue wire going into C (like pictured in this thread) when it turns out that the yellow wire was common ground, not blue. That’s also why I wasn’t getting a power reading on the red wire because my black lead wasn’t on the actual ground wire.
Now I just hope the blue wire is indeed supposed to be hooked up to Y.
But the weird thing is going back and looking at the pictures I took of the original wiring, blue was definitely going into C and yellow into Y. ???
Given the confusion here I would recommend looking at the HVAC end at the terminals to see if you can positively trace and identify the wire connecting to the C terminal there.
It would be very odd for the yellow to be used for this, but not impossible, and some installers may be either inexperienced and unaware or unconcerned with color coding the wiring.
Well the unit is not actually cooling when set to cool. This makes me thing the wiring is still messed up somehow.
I went back to the hvac on the roof to check on the wires at the source. There they are:
Yellow = Y
Blue = Y2
BROWN = C
I hadn’t had the brown wire hooked up at all, as it wasn’t(?!) connected to the old thermostat.
I also confirmed at the HVAC unit that the color of wires did not change from the pcb connector to the wires running to the thermostat in the house.
I went down and swapped the wires in the thermostat to match the hvac unit.
With this new configuration the power is working, but either it’s not getting cold or the t40K sensor isn’t responding properly?
That wiring means that brown should be connected to C at the thermostat. Your HVAC has two stages of cooling.
but either it’s not getting cold or the t40K sensor isn’t responding properly?
To clarify, are you having trouble getting the cool stages to kick on, or the air blowing is not cold?
Make sure that with all the changes that your thermostat is configured appropriately based on the type of HVAC, number of stages, etc. You can find that configuration by visiting the thermostat page in Alarm.com and navigating to Advanced Configuration
