Heat Pump/Honeywell T-stat Wiring Questions


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Old 06-21-11, 05:08 AM
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Heat Pump/Honeywell T-stat Wiring Questions

Hi guys, been searching around looking for an answer but figured I'd better run things by the experts.

I'm helping a friend out - She has a heat pump and an outdoor AC unit. I'm really not familiar with her system, so I can't provide any details at this time.
She came home to a old Honeywell T8411R thermostat with a blank screen. I figured the stat had run it's course and a new one would fix things. I was attempting to replace the old with a new Honeywell RTH2510 battery powered stat.

Wiring is as follows:

Wire----Old Terminal
Green------G
Blue-------C
Red--------R
Yellow-----Y and jumped to W1
White-----W2 and jumped to E
Orange----O
The L and B terminals were not used

My research tells me I need to check for 24V across C and R to ensure it was the old T-stat that went. I won't be able to get into the house again until this coming weekend.

I wired the new T-stat as follows, with no luck.
Wire --------New Terminal
Orange--------O
Yellow--------Y
Red-----------R with jumper to RC in place
Green--------G
White-------W/Aux
I taped off the Blue wire

Any idea on where I went wrong with this install?
Thanks in advance for any help you guys can provide. I appreciate it.
 
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Old 06-21-11, 07:32 AM
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You do have it wired correct. I'd check for power as you said. If you don't have power, then you need to go to the furnace/air handler and go from there.

FIY, the new stat does not have "Emergency Heat" switch. If you got the power back, best to keep the old stat since it has that switch, and it's non-program.
 
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Old 06-21-11, 08:54 AM
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Thanks for the quick feedback.

To start, I'll check for power at the wall. I was under the impression that the blue wire provided power to the thermostat, but if using a battery powered one does it matter? Or does this signify a bigger issue at the furnace/handler?

I'll head back to the store and find a programmable T-stat that will work with emergency heat.
 
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Old 06-21-11, 09:31 AM
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R and your power and C is common. R will also run the equipment. So if you have no power on R then the system won't run.

HP is best to "Set it and forget it" but if you put it on HOLD, and the RTH7500/7600 will work.
 
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Old 06-27-11, 07:26 AM
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I checked for power across R and C (red and blue wires) and came up with zero. I'm assuming that there is supposed to be power there at all times. Not sure where to go from here? Time to call a pro?

Thank you.
 
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Old 06-27-11, 07:45 AM
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If you don't have power...it's normally a pretty easy fix. Up where the air handler is, go and trace the stat wires....normally they'll go to a simple connection box of some sort or directly into the air handler. There should be a way to follow them til you find the transformer that provides the voltage. Some of them are fused, some aren't. Either way it's a pretty cheap fix if thats the problem.


I'm a bit confused...but then I'm not a thermostat expert like Jay. Seems like by taping off the blue you lost 1/2 your circuit? But since you checked the wires themselves...guess it's not an issue. I believe this is an A/C voltage as well (?? I think?)...make sure your meter is set right.

Also...just to get to the basics....did you check all the breakers/fuses in the panel? You could be doing a lot for no gain.
 
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Old 06-27-11, 11:28 AM
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Yes, I had the multimeter set to AC voltage, and I first ensured that none of the breakers had been tripped.

I'll take a look at the air handler electronics later on tonight to get an idea of a fuse block there that may be the culprit.
Thanks again guys.
 
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Old 06-27-11, 11:35 AM
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It's not really a fuse block I don't think...it's wired right at the xformer...not sure if its on the input or output side. Thats just from my reading here.

Find the xfmr...check the input for 120..then check the output.
 
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Old 06-27-11, 02:22 PM
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If you are reading on R and C hooked up on the old stat, then you need to trace back like Gunguy pointed out.

Some brand has fuse, and others don't on the low voltage side of the system. Check to make sure the air handler has power to it.
 
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Old 07-11-11, 05:33 AM
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I got in the crawlspace over the weekend and checked the following:
1. No power at R and C at the terminal block on the air handler.
2. No power across the terminals labeled 24V and C at the AH
3. I checked the breaker box to make sure it wasn't a bad breaker. Power is good there.
4. The fuse at the transformer also checked out good

What I didn't check was to make sure there was power at the transformer. I'll have to get back under there.

Thanks again.
Jay
 
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Old 07-11-11, 06:21 AM
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Check power going into the unit. At the transformer and after the transformer.
 
 

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