Thermostat wiring question (Heil heatpump and White-Rodgers stat)

Hello all, I'm hoping someone here can help.
I am attempting to replace my current thermostat (mercury type) with a White-Rodgers 1f82-261. The current stat is wired with 4 wires; red->'r', green->'g', yellow->'y' and orange->'o'. The new stat requires 24v power from the system which means I need to get the common side of the trans back to the stat. The cable at the wall has 7 wires in it. When I put a meter on the red and blue wires I show 24vac. I opened the panel on the heatpump (Heil) and the blue wire is not connected to anything so I'm left wondering how the circuit is being completed.
Do the control wires typically connect to something else (transformer?) between the heatpump and thermostat? I had assumed the transformer is located within the heatpump and the 24vac is supplied via the red wire to the stat which then determines which path it returns on. Is that correct? If so, I was thinking I could just connect the common side of the transformer to the blue wire and violla. Since I'm already showing a circuit with the blue and red, and the blue is not connected at the heatpump side, I'm stumped.
Any help is appreciated!
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Dave wrote:

Obviously, it is a different blue wire.
You are over your head and may be better off calling a professional before you let the magic smoke out of something.
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Yes, obviously, but I guess I didn't make it clear that I had already figured that out. My question was:
"Do the control wires typically connect to something else (transformer?) between the heatpump and thermostat? I had assumed the transformer is located within the heatpump and the 24vac is supplied via the red wire to the stat which then determines which path it returns on. Is that correct?"
What I'm getting at is do I need to start looking for a transformer outside of the heatpump that feeds the 24vac or are my assumptions correct about thermostat wiring in general and it's just that the wiring on this set-up completely jacked?
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Dave wrote:

No.
Yes.
Your wiring sounds fine, but you're looking in the wrong place. If the solution isn't obvious, please call a professional.
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Dave wrote:

The transformer is located in the air handler. The open end of the unused blue is probably just touching some sheet metal in the control section, thus grounding it. It shouldn't be tied in at the t-stat until it has been confirmed that it's connected to the transformer common. If the house burns because of your negligence your HO insurance may not cover it.
hvacrmedic
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Understood.
You're the only one here to inform me that the transformer is in the air handler. I had the same idea that the wire was grounding out somewhere and I capped it when I was looking at the heat pump end just to be sure. Since I was still showing a circuit, I knew there was a connection somewhere else, but didn't know where.
I ended up getting a non-power stealing stat, so I've managed a work around. I appreciate the info as it will come in handy if I ever come across this again.
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Dave wrote:

Hi, Reading this line, I think you need pro's help. Don't do it yourself. Tony

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Why are people so reluctant to answer a question? "Don't do it yourself" is not an answer to my question. At least explain why you think I shouldn't do it myself. Otherwise, why bother replying? I already know that calling a pro is an option so I'm no more enlightened about my situation than I was before I read your post.
Regardless, I ended up getting a stat that uses battery power. It's a Robertshaw 8600 and while it's not the most quality product I've ever handled, for $35 I can't complain. It works, is programmable (5/2) and has a backlight.
Thanks to those that offered help and information.
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Dave Not all brands use the same control system for heat pumps. Many have special wiring requirements. The common is often blue, but some use brown or black. The electrons don't really care what color insulation is on the wire, it just makes it easier to service.
R=red$ Volts Hot Y=Yellow=Compressor Contactor W=White=Strip Heat G=Green=Indoor Blower O=Orange=Reversing Valve Energised in Cool Mode B=Blue$ Volts Common
There may be other wires for service lites, but that is normal wiring for Heil.
R,W,G,B connect at the indoor unit, All 6 connect to the thermostat, All but G connect to the outdoor unit. If yoy don't keep the color code consistant, you could fry something. If there is a splice in the cable where there is a color change, you will most likely need a meter anf know how to use it.
Other brands like Rheem/Ruud, Amana, Weather King use completely different systems.
Setback thermostats work best when equipment is too big. If your heat pump is properly sized, you will not have enough capacity to do recovery, especially in heat mode.
How you heated your home without strips in extremely cold weather I don't know. You must live in a mild climate.
Stretch
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Right. :) I assume you are being facetious here. I'm familiar with electrical systems in general so I grasp the basic connection part. I've never delved into HVAC systems except for a prior stat replacement which worked right out of the gate. I haven't had to troubleshoot them or track their wiring down.

One word - Phoenix. ;) I used the heat about 5 times over the "winter" here, so a heat pump is mostly sufficient for the task. The problem I ran into is I wouldn't turn it on until it was about 60 inside and 30 outside, so it would have to run forever before it would start blowing something resembling tepid air.
Thanks for the informative reply!
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