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Kcrand36
Kcrand36, HVAC Mechanic
Category: HVAC
Satisfied Customers: 67
Experience:  Owner at Advantage Repair
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I attempted to replace a York thermostat with a Sensi WiFi

Customer Question

I attempted to replace a York thermostat with a Sensi WiFi digital and it didn't work so I put the old thermostat back. And now it doesn't work. No 24vac to thermostat. I double checked the wiring and it correct. I have a photo to go by.
Any suggestions?
Submitted: 1 year ago.
Category: HVAC
Expert:  Kcrand36 replied 1 year ago.

Hi Kenneth, I am Kevin. when you attempted to change the thermostat, did you power off the Air handler before doing so?

Customer: replied 1 year ago.
Expert:  Kcrand36 replied 1 year ago.

I tried pulling up your particular model number, but can't seem to find it. How old is your system? Heat Pump ? Split system, meaning you have an indoor blower unit?

Customer: replied 1 year ago.
I turned both AC and Furnace breakers off. It's about 15 years old and has an Inside air handler and a outside compressor unit.
Expert:  Kcrand36 replied 1 year ago.

now you are experiencing no power to the tstat correct?

Customer: replied 1 year ago.
I checked it with a meter, and also do not see the mercury switches "spark" when they make connection. My thermostat is a York T874g1170.
Expert:  Kcrand36 replied 1 year ago.

well, your right about that, your t874 is an antique in these days, what is the furnace model #? I think I would start there first.

Customer: replied 1 year ago.
It's a York Heat Pump with Heat Strips for aux/emergency heating. The circuit breaker is labeled "Furnace". Didn't mean to confuse you. I only have the single system outside.
Expert:  Kcrand36 replied 1 year ago.

ok, no problem, I was able to pull up the outdoor unit, or at least what I though so, and it did say Heat Pump. I would still like to see if we can get the model number off the indoor blower unit with the electric strips. That may be where are problem is.

Customer: replied 1 year ago.
I am sending you a pix of the nameplate.
Expert:  Kcrand36 replied 1 year ago.

both pictures you sent me are of the outdoor unit?

Customer: replied 1 year ago.
I sent 2 copies by mistake. My inside unit is in the attic and hard to get to.
Expert:  Kcrand36 replied 1 year ago.

unfortunately, I believe your problem is there. You may have blown a fuse if installed, or shorted the transformer.

Customer: replied 1 year ago.
Does the York Module supply the AC for the thermostat? Can I check on the Outside somewhere to locate this 24vac for the thermostat?
Expert:  Kcrand36 replied 1 year ago.

Usually, the thermostat power comes from the Air Handler, many mfr's are different, such as carrier, who sometimes use 2 transformers. Without knowing the model # ***** the air handler, I would not be able to tell you.

Customer: replied 1 year ago.
Is it logical to suspect this module, or could it be something else? My thermostat appears to be wired directly to this module. Here is a Pix of the module and the color code on the module corresponds to the wiring on the thermostat.
Expert:  Kcrand36 replied 1 year ago.

ok, I see the module, can you take a much wider picture of what other components may be installed?

Customer: replied 1 year ago.
but I will need to take the panel back off. Will take a few minutes. Can you wait?
Expert:  Kcrand36 replied 1 year ago.

certainly, I would rather fix this now if possible.

Customer: replied 1 year ago.
While your waiting here are a couple of pixs of the schematic on the cover panel.
Expert:  Kcrand36 replied 1 year ago.

do you have a voltmeter, and know how to test?

Expert:  Kcrand36 replied 1 year ago.

Kenneth, I think I have your answer......

Customer: replied 1 year ago.
Here are 5 pixs, hope they are of some help.
Expert:  Kcrand36 replied 1 year ago.

do you have voltmeter and can test for power on 2 terminals?

Customer: replied 1 year ago.
Expert:  Kcrand36 replied 1 year ago.

great, can you test on the yorkguard module, terminals R and B for voltage?

Customer: replied 1 year ago.
The unit is powered off, and I have Duke Energy Load control so it takes approx. 10-15 min. for the load control to time out and restore AC power to the unit.
Expert:  Kcrand36 replied 1 year ago.

if power is off to the outdoor unit, I am not concerned....... Only the indoor unit if that has been on, then we should know. But if you wish to wait the 15 minutes I don't have a problem.

Customer: replied 1 year ago.
The 2 units are powered from the same breakers. I cannot turn them on independently.
Expert:  Kcrand36 replied 1 year ago.

ok, just let me know when you have power to the outdoor unit.

Customer: replied 1 year ago.
OK. Just to verify, terminals R and B are the Red and Blue wires.
Expert:  Kcrand36 replied 1 year ago.

not sure of the colors, because they are field installed, but they are labeled R and B respectively on the module.

Expert:  Kcrand36 replied 1 year ago.

and we want to check R and B on the left side of the module, and then again the R and B on the bottom of the module.

Customer: replied 1 year ago.
No voltage AC or DC on R and B, or any of the terminals.
Expert:  Kcrand36 replied 1 year ago.

your problem comes from the air handler in the attic.... I'm sorry to give you that news, but you have to go there. I will send you a print .

Customer: replied 1 year ago.
I only see the terminal on the bottom left side. Please explain the R and B at the bottom.
Expert:  Kcrand36 replied 1 year ago.

I'm showing 6 terminals on the bottom, maybe hard wired to the (outdoor unit) then 3 pairs of wires for sensors (heat pump defrost control). to the right of those. The R and B are showing hard wired through the module via the print I sent you. If you can get up there and get the model # ***** that unit, maybe pull of a door to the electrical compartment, we might be able to determine the failed part.

Expert:  Kcrand36 replied 1 year ago.

I'm showing 6 terminals on the bottom, maybe hard wired to the (outdoor unit) then 3 pairs of wires for sensors (heat pump defrost control). to the right of those. The R and B are showing hard wired through the module via the print I sent you. If you can get up there and get the model # ***** that unit, maybe pull of a door to the electrical compartment, we might be able to determine the failed part.

Expert:  Kcrand36 replied 1 year ago.

Hi Kenneth, please don't forget to rate the service you have received. It is important to do so for the continued support. thank you

Kevin

Expert:  Kcrand36 replied 1 year ago.

Hi Kenneth, just following up to see how you have made out. Have you gotten your transformer/fan center replaced in the attic unit? If you still have a problem feel free to come back to the open call. If you have solved your problem, please take the time to rate the service you have received, so I may close the call on my end.

Thank you

Kevin. Happy Holidays!

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