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Source of stray voltage?

2424 Views 7 Replies 3 Participants Last post by  gene2
Goodman HP: (RV energized in cool mode), for some reason, the orange wire is getting 18 volts when system calls for heat with stat connected, and 12v when faceplate is removed and R&Y are tied together.

  • Checked wiring all appears good.
  • Checked wires and disconnected to see if there was a possible short..none
  • Checked did a continuity test on the appropriate prongs of the stat and all was as it should be. (battery powered, but also has a c terminal)
  • Took a new stat off the truck (honeywell t6110 with h.p capabilities w/o aux heat) energized system in heat mode & again, 18v to o wire in heat mode
Now here is the another kicker:

  • kept tstat2 backplate connected, and pigtailed tstat1 to r,w,y,c & O wires at the heat pump.
  • energized heat mode. I read 0volts between o&c at the h/p board and 0 volts at backplate2, and got the correct readings between r&c, as well as y&c.
Any ideas why I am getting a voltage reading when stats are inside the home as opposed to outside? Some may say who cares if you are getting 12v or even 18v, but the bottom line is that the rv is getting energized in heat mode.

Also, some people may cringe at the prospect of energizing and de-energizing a heat pump a bunch of times... The high voltage at the h.p was disconnected. ;)
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Try removing the Defrost Circuit Board. I have found many times a defective CB can cause such strangeness.
If that doesn't help, disconnect all thermostat cables to Tstsat, Indoor & Outdoor then run a megohmeter between all wires. I would do that before buying a circuit board.
If you don't have the problem when you use the old stat by wiring it up at the outside unit. It tends to indicate that the problem is in the wires from the stat location.
If you don't have the problem when you use the old stat by wiring it up at the outside unit. It tends to indicate that the problem is in the wires from the stat location.
The thing about the wiring at the stat is that I kept the back plate of t-stat2 connected while "using" t-stat one at the heat pump.

At that point, I got normal readings both on the wires to the hp and normal readings on back plate-2. That is what has me stumped. If the wiring was faulty, wouldn't you expect to have the same problem?

I tried several wiring configurations: (hardwired wires at stat, wired r @ the a/h to y to the heat pump and kept the stat wires out of the circuit, and always there was voltage on the o wire). I never even thought about by-passing the defrost board on the heat pump.... Not only should I say thanks to Gene, but Thanks a lot:thumbup:.

Well, I left the o-wire as a temporary fix, but thanks to B.T. and Gene, I have some better ideas.
Sometimes. The wires in the wall can be shorting when the stat is on. but, when you remove the stat, it takes just enough pressure off the wires. that they no longer touch,
I am returning on Monday. Again, thanks for the input. I don't like to use anybody as a crutch, but it's nice to have someplace to go to when being stumped. Sometimes, the manufacturer tech guys, and local supply guys just aren't sure themselves.

Always learning..:)
I also forgot, sometimes a sub base will have a faulty diode allowing feedback. Not applicable in this case though.

Even us old guys get stumped sometimes. The factory techs are limited by diagnosing over the phone.

There is always something new to learn in this trade even on the older proven technologys. The new technology coming everyday presents even more challenges.

That's what I enjoy on forums like this. An exchange of ideas & solutions.
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