Hi Folks,
I wish you thank you all for helping me do the above-mentioned transition successfully yesterday, particularly hvac1000. My new Honeywell VisionPRO 8000 can be powered by 3-AAA batteries or 24Vac. Currently,I am using 3-AAA batteries to power up the Honeywell thermostat and it works great. However, when the batteries run out of power, I have to install three new 3-AAA batteries that I do not mine.
However, there is an option to use 24Vac from the wall. According to the Honeywell VisionPRO 8000 manual, this is the common wire from the secondary side of the cooling transformer (if 2 transformers) which my system is. From the wiring diagram of the White-Rodgers 5-wire heating/cooling system, one of the wires RC goes to the cooling transformer in the wiring diagram. I assumed this was the wire that has to go the common C terminal on the Honeywell VisionPRO 8000. However, when I move this wire from the RC terminal on the Honeywell to the C terminal on the honeywell, everything being the same, the Honeywell VisionPRO 8000 does not power up when I remove the 3-AAA batteries from the Honeywell VisionPRO 8000. Currently five independent wires are going to the following terminals: RC, R, Y, G and white. The common C terminal is open and unit works excellently (both heating and cooling works with the current wiring with three 3-AAA batteries as my source of power for the Honeywell thermostat).
Any help will be greatly appreciated.

Thanks,
Eric.

1H/1C System (2 transformers)
Rc Power (cooling transformer) [1, 2]
R Power (heating transformer) [1, 2]
W Heat relay
Y Compressor contactor
G Fan relay
C 24VAC common [3, 4]
S1 Optional outdoor/remote sensor
S2 Optional outdoor/remote sensor


See [notes] below
[1] Power supply. Provide disconnect means and overload protection as required.
[2] Remove jumper for 2-transformer systems.
[3] Optional 24VAC common connection.
[4] Common connection must come from cooling transformer.

hvac1000.
I know this already and have the installation manuals. Either the 24Vac or battery could be optional power. In my current set up, the 24Vac is optional power as indicated in the thermostat installation manual. I just want to use the 24Vac so that I can avoid battery purchases if possible.

Thanks,
Eric.

Then feed the C terminal with a 24 volt COMMON source. If you read the instructions it says


C 24VAC common [3, 4]

Then it says


[3] Optional 24VAC common connection.
[4] Common connection must come from cooling transformer.

Now that is the way it is and this is the way I hook them up unless you have something wired incorrectly. IE find a unused wire in the thermostat wiring OR run a additional wire.

PS common is the negative side and you only have positive voltage at the thermostat now. You need a common leg from the other side of the cooling transformer brought to thermostat. IE find a unused wire in the thermostat cable or add a wire.

I do not have the skill to run an additional wire for the Common C. As an Electrotechnologist that has spent the last 15 years in the computer industry, I will not take chance with anything. The current wiring works for both cooling and heating, so I will leave it as is. On the other hand, I do not want to pay for this job.Anyway, if an additional wire has to be added, where is it coming from? My furnace and the electricity control panels are in the basemnt, my central air conditioner is outside and my thermostat wiring is in front of my living room.

Cheers,
Eric.

hvac1000,
I thought of putting a wire from the RC terminal on the thermostat plate to the C terminal on the thermostat plate.However, this sounded like shorting the two terminals. Since I have read about other people's demise in installing electronic thermostat's, I did not want to risk anything.
If this is incorrect, please give me your professional advice. May be, I do not understand what I am reading.

Thanks,
Eric.

Don't do it. Find the Y wire at the furnace. It should be connected to another tstat cable that heads outside and we'll go from there.

I am keeping everything as is because it works. I shall look into the 24Vac common connection if I feel it can safely be done.

Most of the time regular tstat wire does not have any extra wires to use. Pulling a extra wire can be a pain and I have had to do that many times.

hvac1000,
From the wiring diagram of the White-Rodgers 1E56W-309, there is a 24Vac line that goes to the Y-wire (cooling system) and G-wire(Fan relay) for the 5-wire, heating/cooling 2-transformer system that I have. In the absence of a common C wire, can I tap 24Vac from the Y-wire of the cooling system to use in the common C-terminal? Please note that in the wiring diagram, the Y and G wires are connected to a common 24Vac from the cooling transformer.

Thanks in advance,
Eric.

What I am trying to tell you to do (cell phone typing before) is to LOCATE the tstat cable going to the outside unit. It should be in the furnace. The furnace acts like a junction box between the tstat, the furnace and the outside unit.

In most cases the outside unit needs two wires to work. A Common and Y. That's the Common you need you need to connect to the VP common terminal.

What you need to do, is go to the furnace and LOCATE the two tstat cables going to it. One heads outside and one goes to the tstat.

Both Y and G are already being used as a + signal circuit FROM the thermostat to the Fan=G and the outside condenser=Y.

There is NO WAY to cheat and get the extra wire or connection you need without causing other MAJOR problems. Smarter people than you have already looked at all reasonable possibilities! BTW the Y and G are + power sources that send signals away from the thermostat and you need a - source that does not send a signal but allows completion of a 24 volt power supply for the thermostat. You need another wire which you do not have to complete the proper wiring of the thermostat if you want to use the 24 volts from the transformer to power the thermostat instead of using the battery's.

Nuff said and class on this subject is over for today. When you get your other wire run post back and we will direct you as to where to hook it up. Keep it simple is on the right track for the common side that you will need to connect your NEW wire to for the system to operate properly.

What you have now is a lot better than this guy.

hvac1000,
You have proofed being an HVAC tech again. I was just brain storming. I am not going to change my current wiring. It works excellently and this is the last time I am going to post on this. I am keeping everything as-is and again thanks a million for all the trouble and answers I got out of you.
Stay blessed and continue your good work.

Thanks a million again,
Eric.

NO problem.

From PM:

Quote:

---

Originally Posted by eosei

The Y-wire comes to the thermostat electrical plate. The Y-wire is connected to a 24Vac from the cooling transformer. The G-wire is also connected to the 24Vac from the cooling transformer also. However, I do not know if it is electrically safe to tap 24Vac from here to the common C-terminal.

Thanks,
Eric.

---

Rc is coming from one end of the secondary of the transformer. Y and G are coming from the stat. Y is Connected to Rc when there is a call for cool. G is connected to Rc when there is a call for fan. A call for cool automatically energises the fan.

What this means is that there is a wire from that transformer that is conncted to the outside unit and the fan relay. Since it's conncted to two things it's called COMMON. This is the point you need.

So you mean I can connect an 18 gauge wire from wire Y (connected to the cooling system) to the C-terminal on the thermostat plate and that should be able to power up the electronic thermostat in the absence of C-wire from the old White-Rogers 1E56W-309 thermostat.
Did I undestand your posting?

Thanks.
Eric.

no. that would be the same as jumping y to c on stat. You will need five stat wires from furnace to stat for stat to be powered by furnace transformer. If you only have four wires, your out of luck. The batterys in your stat will last for a long time, if you don't want to pull another wire, keep things as they are, and just change your batteries once a year.

You are right. I am just brain storming. Like I said before, my current wiring works for both heating and cooling with thermostat powered by 3-AAA batteries. I have five wires though not 4 as you suggested. These are RC, RH. Y, W and G. No common C wire.

Cheers,
Eric.

Mygirlsdad:

You were not paying attention to the entire thread. This is a TWO transformer system. Uses both Rc and Rh separately, not jumped together.

There is always a gotcha. Gotcha!