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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22090
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I am trying to install a RTF 9580WF Thermostat on a Trane

Customer Question

I am trying to install a RTF 9580WF Thermostat on a Trane HVAC system. I have confirmed a C wire is connected at the FAU. I am completing the install in basic method. Red-Red, Green-Green, White-White, Yellow-Yellow. Com (blue)- Com (blue).
Upon completion I have no power to the thermostat. Help.....
Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.

Hello, do you have a volt meter?

Expert:  BillyHvac replied 1 year ago.

Hello,

This is likely a blown fuse in the unit on the circuit board or inline from the transformer. The fuse on board would be a blade type fuse like found in a car. If inline it is a small tube fuse in the wire off transformer. Is this a YCD unit?

Customer: replied 1 year ago.
The system is still working with old thermostat. The blue (C) wire was not connected with the current Thermostat but is connected to the Com on the FAU. It feels like it has juice in it.So to reiterate. Red-Red, Green-Green-White-White, Yellow-Yellow, C (blue) was not connected on thermostat but connected at FAU. Unit is running with old thermostat put back on. Not with new one (with C wire connected).
Expert:  BillyHvac replied 1 year ago.

so C is NOT connected in the wifi stat? Or you had C connected at unit and at thermostat yet it did not power up?

Customer: replied 1 year ago.
When I had the connected to both the Thermostat and the FAU it did not work (all other wires connected as well). I removed the new thermostat and reinstalled the old (no C wire) and unit is working fine.
Expert:  BillyHvac replied 1 year ago.

thank you. And at the unit...the blue wire is actually attached to a C terminal?

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

And is there a rc rh in thermostat (wifi) connected with a short jumper?

Customer: replied 1 year ago.
Only thing I can think is that maybe the blue wire has a break in it. I have a line tester that I can test it. I thought it must be something with the setup but sounds like I got that part right.On the unit, the C line is also powering another thermostat for a zone on same system.
Expert:  BillyHvac replied 1 year ago.

is there a zone control box?

Customer: replied 1 year ago.
Must be but I don't know what that is. It has 2 zones.
Expert:  BillyHvac replied 1 year ago.

ok, we need to trace the thermostat wire from the furnace...if zoned..it goes to a zone panel first..then the the stat.

Customer: replied 1 year ago.
for reference, I tried it on another unit (3 in our house) that is not zoned and I confirmed the blue wire was connected to the C terminal. Still did not work when all wires connected (including C)
Expert:  BillyHvac replied 1 year ago.

a zone panel is where we need to check for thermostat wiring...furnace wires to panel...then panel wires to thermostats

Customer: replied 1 year ago.
OK. I'll check but not until morning. It is 102 here right now. Not going into attic again til it cools....I can pick this up after. I am still confused as the other unit was not zoned and it still did not work.....
Expert:  BillyHvac replied 1 year ago.

once I know what zone panel you have I can direct further

Customer: replied 1 year ago.
Can I pick this up tomorrow?
Expert:  BillyHvac replied 1 year ago.

because power for thermostats comes from the panel...not the furnace...at furnace you are looking at zone panel wiring..not thermostat....the furnace wires to the panel....then all thermostats connect to the panel on similiar terminals like found in furnace...tommorrow is fine

Customer: replied 1 year ago.
sir
Expert:  BillyHvac replied 1 year ago.

just keep this on your end until tomorrow or it will force a response from my end. Just hold until you are ready tomorrow.

Billy

Customer: replied 1 year ago.
OK. NOW I GET IT!ZTech Box. Photo attached. Wire from FAU coming in and connected to 24v on upper right. Unconnected Blue wire on opposite side. There is no 24v on opposite side (12v lower left), do I jump the Blue Com wire over to the 24v on the right side?
Expert:  BillyHvac replied 1 year ago.

Ok we are close now...unfortunately I could not blow the pic up clearly..does it just say Ztech?

Expert:  BillyHvac replied 1 year ago.

where the thermostat attaches...do you have 24v R and 24v C?

Customer: replied 1 year ago.
It says is is a 2 Zone cControl with Smart Vent Here is a better pictureModel (I think) @ or Z C82
Expert:  BillyHvac replied 1 year ago.

far right upper corner blue and black wire...do they go by themselves to a transformer?

And on left side do you see com?

Customer: replied 1 year ago.
Upper Right:Power - Blue Wire to FAU 24C Black Wire Junped to Zone 2 RHOn Thermostat Side (Left)Com- S485 12v / GND / D+ / D-I took better pictures if that would help.
Expert:  BillyHvac replied 1 year ago.

ok, your thermostat C wires need to connect to the 24c black wire. You can install one wire and then wire nut others to it. Or if you see a 24v c or com on the board we can use that.

Customer: replied 1 year ago.
working on it. Thought I connected. Still nothing. Going back up
Customer: replied 1 year ago.
Ok. I got connected to the upper right 24C PWR on FAU side (All blue wires on my photo - the Black wire is 24R). I have power to the Thermostat but it is pulsing on and off. 5 seconds on, then off.
Customer: replied 1 year ago.
Here is wiring diagram. I am connected to upper right 24v Com. Not sure why pulsing.
Expert:  BillyHvac replied 1 year ago.

does the blue wire go to the furnace or to a different transformer?