Thermostat wiring question

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  #1  
Old 10-01-07, 01:44 PM
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Thermostat wiring question

My thermostat does not work properly. I bought a new one from the homedepot. When I opened the old one, I found the white and blue wires on the thermostat were wired together into the W terminal. Is that normal? There is a B terminal on the old one. Here are the connections.

Red wire -- R terminal (jumpered with Rc)
Yellow -- Y terminal
Green -- G terminal
White & Blue -- W terminal.

B and O terminals are free.

I have electric heating (Bryant) and a compressor (rheem) for cooling.
 
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Old 10-01-07, 05:03 PM
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Make sure that the wires are on the same terminal designations on the furnace. I'd hazard to guess that because you use electric heat, the two wires under W go to the heating contactor and the fan contactor. Normally a gas furnace takes care of it's own fan start.
 
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Old 10-01-07, 05:43 PM
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Originally Posted by gremlin View Post
Make sure that the wires are on the same terminal designations on the furnace. I'd hazard to guess that because you use electric heat, the two wires under W go to the heating contactor and the fan contactor. Normally a gas furnace takes care of it's own fan start.

Some systems need an electric heat subbase [translation- auto fan with a call for heat] while others bring the fan on at a lower speed via an electric heat sequencer. What stat did you buy at HD?
 
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Old 10-02-07, 07:02 AM
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I opened the furnace and looked at the wire connections. The diagram shows three heatstrips. The yellow wire from thermostat connects to a contactor which has a 120-vac wire to the top heatstrip. The blue wire from thermostat connects to a contactor which has two 120-vac wires to the middle and bottom heatstrips separately. looks like a pretty odd design, why can't all heatstrips be controlled by one wire from the thermostat.
I bought a Honeywell thermostat from HD. It says OK for a/c, heating, and heatpump. Do you think I need a special type of thermostat for the design?
 
  #5  
Old 10-02-07, 07:24 AM
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A picture would help. But it sounds like whoever wired this was thinking 2 stage electric heat. Anyway, it appears to be ok to wire the blue and white wires to the "w" terminal.

Yes, all heat strips could be controlled by one wire if you wanted to do that. But don't change anything for now.

Be sure the stat is programmed for electric heat rather than heat pump.
 
  #6  
Old 10-03-07, 06:51 AM
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Sorry I couldn't get the picture to my PC because of some software problem.

I think you're right. It looks like a 2-stage electric heat, but one stage failed. I connected only the white wire to the W terminal on the stat, stat calling for heat, fan started, but no hot air at all after a while. The 120vac power went through the contact going to the top heatstrip, but there is no continuity between two terminals of the top heatstrip when I tested it with a meter. When I connect the blue wire also to the W terminal on the stat, stat calling for heat, fan started, and hot air came out in less than a minute. There are continuity between the two terminals of the each bottom heatstrip. The hot air reached about 120F and stayed around that eventually (room temperature was around 80 at the test), I hope that's OK.

The contactor connected to the blue wire in the furnace is a weird kind. All its terminals have 120vac when heating is not running, the power goes to the heatstrip terminals, but the two heatstrips it connects to are both off. When the blue wire got 24vac, the contactor did some magic to turn on the heatstrips. Is that contactor OK?

I'll make sure the stat is programmed for electric heat. Thank you!
 
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Old 10-03-07, 07:58 AM
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Wink

There is a B terminal on the old one.
[QUOTEThe contactor connected to the blue wire in the furnace is a weird kind. All its terminals have 120vac when heating is not running, the power goes to the heatstrip terminals, but the two heatstrips it connects to are both off. When the blue wire got 24vac, the contactor did some magic to turn on the heatstrips. Is that contactor OK?
][/QUOTE]
Do you have a heatpump here or not?????

The 120vac power went through the contact going to the top heatstrip, but there is no continuity between two terminals of the top heatstrip when I tested it with a meter.
With electric heat across the terminals when on you should have 220V . when the power to them is off you should read 110V to ground
If you Ohm it out and no continuity on the coil . There is a small fuse in the element that can be out.

When the blue wire got 24vac, the contactor did some magic to turn on the heatstrips. Is that contactor OK?
 
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Old 10-03-07, 08:37 AM
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Ed,
Your replay actually resolved the clouds in my mind about the contactor (I called it "weird kind"). Yes, there is 110V to ground on all terminals of the bottom two heatstips when heating is not running. It must be 220V when on (I haven't measured the voltage when heater running).

I didn't see fuses, I bet it's inside the heatstrip enclosure. I don't want to mess with it. I'll call a technician for it later.

No. I don't have a heatpump. The B terminal on the old stat was not connected to anywhere. I first thought it might be for blue wire, but after some reading, I figured out it's for heatpump.

Thank you very much!
 
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