Carrier TC-PAC01 Wiring

[kev1951]

I recently installed a Carrier thermostat, TC-PAC01. My question concerns the wire attached to the C terminal of the thermostat. To what terminal is the wire attached at the furnace? Details follow.

The TC-PAC01 replaces an old programmable thermostat which used batteries. I am running only heat (oil, forced air) with one zone, no AC. The old thermostat had only two wires attached, red to the Rh terminal and white to the W terminal. A third wire was present but not attached.




I would like to run the TC-PAC01 off the furnace’s 24V power and so attached the third wire to the TC-PAC01’s C terminal. However, at the furnace the third wire is not attached to any terminal and so the TC-PAC01 still requires batteries to operate.

At the furnace I have a Honeywell transformer with four terminals, two marked F to which yellow wires are attached. The other two terminals on the transformer are marked T and the red and white wires from the TC-PAC01 are attached there.

So, where do I attach the C wire from the thermostat?

Thanks for any help.

[Servicetech]

If you post photos, it would be easier for us to be able to help you.

[kev1951]

If you post photos, it would be easier for us to be able to help you.

Ok, here are some pics. (note: I have not attempted to upload pics to this site before; it looks like it worked, please let me know if it didn't.)

The first pics show the thermostat wiring. From top to bottom, the terminals are labelled as follows, with their status in my set-up in parentheses and then the Carrier description of each terminal:

Rc (jumpered to Rh) 24 VAC, from cooling equipment
Rh (red wire attached) 24 VAC, from heating equipment
W (white wire attached) Heating
C (third, previously unused wire attached) Common 24 VAC
G (empty) Fan
Y (empty) Cooling

Then there are some pics of the transformer. You can see the 4 terminals, two labelled F with yellow wires attached and two labelled T with the red and white wires attached. You can make out the third unattached wire.

[kev1951]

One more bit of info. Here are the Carrier wiring instructions. Note that I'm not running cooling so there is no separate cooling transformer. I'm wondering if I should disconnect the W wire and hook the C wire to that terminal on the transformer.

[HVAC]

The FF terminals are used for a safety devise most likely a cad cell flame sensor. As you already know there is not a connection for a C wire. You could just connect the green C wire to a ground connection. Find a good ground point around the terminal strip and connect the C wire to it. I would also suggest that you use a multi meter and verify which T terminal has 24vac and make sure that it is connected to the RH terminal on the Carrier TC-PAC01 thermostat.

[kev1951]

Thanks for your help HVAC. I haven't gotten it to work yet, but it may just be a question of finding the right ground point.

I also emailed my question to Carrier customer service. Instead of answering a simple wiring question Carrier told me to go ask a dealer. I regard that as completely inadequate customer support from a manufacturer and won't be buying another Carrier product.

The FF terminals are used for a safety devise most likely a cad cell flame sensor. As you already know there is not a connection for a C wire. You could just connect the green C wire to a ground connection. Find a good ground point around the terminal strip and connect the C wire to it. I would also suggest that you use a multi meter and verify which T terminal has 24vac and make sure that it is connected to the RH terminal on the Carrier TC-PAC01 thermostat.