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Thermostat Problem - When I connect the Common Wire All Digits on the display...

Thermostat Problem - When I connect the Common Wire All Digits on the display...

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  #1  
Old 05-15-11, 05:48 PM
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Thermostat Problem - When I connect the Common Wire All Digits on the display...

So I have a thermostat problem. When I connect the common wire, all digits on the display light up. Recently I had a surge of power to my home causing the existing circuit board on my HVAC unit to catch fire. Being that I am very handy with computers I ordered a new circuit board online and proceed to install it.

Everything was going great until I went up to the thermostat and realized that I had a problem. When I look at the display on the Thermostat, everything is lit up, the time is 88:88 AM/PM the Temp is 88. This happens once I send power through the new circuit board. If I disconnect the common, it doesn't act all screwy (the unit does not communicate properly but it does not make the display lit up.

I could get the Heat/Fan/AC all working by jumping the wire at the board.

Here is a link to my thermostat, LuxProProducts

I did try a new thermostat but that did not help the situation. I've looked high and low on the web and haven't been able to find a solution. Hoping that some one here can help.
 
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Old 05-15-11, 06:46 PM
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check the voltage between R & C. should be no higher than 27ish Volts
 
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Old 05-15-11, 06:52 PM
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Thank you for the quick reply if it is higher than what do I do?
 
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Old 05-15-11, 06:55 PM
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replace the transformer. How long does it stay all lit up with common connected? Also, just to be sure, what terminal are you connecting common to?
 
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Old 05-15-11, 07:12 PM
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It stays all light like that until I Hard Reset the Thermostat and as soon as I turn power back on it goes back on.

As far as the terminal that I am connecting the common, I am not sure how to answer that. They are both connected to the "C".
 
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Old 05-15-11, 08:16 PM
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It stays all light like that until I Hard Reset the Thermostat and as soon as I turn power back on it goes back on.
You need to check the voltage then....
As far as the terminal that I am connecting the common, I am not sure how to answer that. They are both connected to the "C".
I was just checking to make sure you were not putting the common wire on RC at the stat.
 
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Old 05-16-11, 09:15 AM
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does your t-stat have batteries? If so when you diconnect the common does the tstat still act crazy?
 
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Old 05-16-11, 09:53 AM
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tell me how you wired the circuit board, i only care about the thermostat and condenser wires. make sure the tstat wires match with the circuit board. please state the color of the wire and what terminal(letter) its connected to
 
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Old 05-16-11, 04:49 PM
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Okay thank you all for the feedback. I went out and Bought a Multimeter. I set it to 2V (DC) and testing my skills out on a Battery got accurate readings for both a AA, and 9V. So I went to the Thermostat, removed the cover and Put one Needle on R and one on C. The Numbers were all over the place from .00- .34 It really did not stay in one place. From what I read that is probably Ambient Voltage. Am I doing the test correctly?

I took some pictures of both the Thermostat and Circuit Board all the wires seem to match up. The original person that wired it used the Yellow Wire for C and the Blue Wire for Y. I switched it on both ends just because, I didn't expect that to help and of course it didn't.











tell me how you wired the circuit board, i only care about the thermostat and condenser wires. make sure the tstat wires match with the circuit board. please state the color of the wire and what terminal(letter) its connected to
I have a picture coming soon hopefully but I did

C - Blue (More of a Cyan though)
Y - Yellow
R - Red
G - Green
W- White

does your t-stat have batteries? If so when you diconnect the common does the tstat still act crazy?
Yes it does have batteries, yes it stays all light up. That is until I Hard Reset it.
 

Last edited by Pandamine; 05-16-11 at 05:11 PM.
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Old 05-16-11, 05:14 PM
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Batteries are DC your furnace and home operate on AC your meter must be set accordingly. Also if you are checking at the furnace then the door switch must be pushed in.
 
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Old 05-16-11, 05:24 PM
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Ahh that was it. The Reading was 28.9

Originally Posted by hvactechfw View Post
Batteries are DC your furnace and home operate on AC your meter must be set accordingly. Also if you are checking at the furnace then the door switch must be pushed in.
 
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Old 05-16-11, 05:40 PM
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that's not horrible depending on the supply voltage to the transformer....You might just replace the thermostat with a quality Honeywell Stat.
 
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Old 05-16-11, 06:01 PM
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Thanks for all the advice, I'll run out tomorrow and pick one up. Are any Honeywell T-Stats better than others?

Originally Posted by hvactechfw View Post
that's not horrible depending on the supply voltage to the transformer....You might just replace the thermostat with a quality Honeywell Stat.
 
  #14  
Old 05-16-11, 06:30 PM
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nah dont bother. the problem is not your tstat. its the way you wired it. your wiring it like you have a heat pump, well u dont. see, your only supposed to be using 4 wires, looks like ur using 5. the four wire to the furnace should be r for red, g for green, y for yellow, and w for white. take the wire off "c" on the furnace circuit board. now you should see 2-wire somewhere around the furnace. this 2 wire(red and white) goes from the furnace to the condenser outside. hook the red wire to "C" and the white wire to "y" that should solve ur problem. and disconnect the wire going to c on the tstat.
 
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Old 05-16-11, 06:46 PM
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not correct ender. You can have C hooked up without having a heat pump. I'm assuming the op hs the ac wired in elsewhere and not at the board. which, then again may be part of the problem since the op said he switched blue and yellow.
 
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