Needs help on thermostat wiring


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Old 10-04-13, 10:19 AM
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Needs help on thermostat wiring

I have an Amana 11 year old 3.5 ton system. Here is the problem:
Room temp (80 degree), I set thermostat at 76 degree & system at AUTO, nothing turned on. set system to FAN only, in house blower turned on, but not outside condenser. Checked contactor,24V was not there, push the button in, condenser turned ON. To my limited knowledge, this may be a Thermostat problem, it is a 11 years old Honeywell. I have a spare thermostat at home, also about 10-12 years old, but different type. wiring is a little different, here is my question:
Current one on the wall has (R,W,Y,G,C,B,O) first 5 wires connected, not B & O. The spare thermostat has (R,W,Y,G,Rc,B,O) terminals. Looks like the difference is Rc and C, are these 2 the same ?? please help.
 
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Old 10-04-13, 11:46 AM
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To test the wiring at the thermostat connect the red, green and yellow wires all together. The indoor fan should run as well as the outdoors condensing unit. If the condensing unit does not run then check for 24 volts AC at the contactor coil connections. If no 24 volts then the wiring is bad somewhere.

The Rc connection on the other thermostat should have a jumper connecting it to the R terminal. Do NOT connect Rc and C together.
 
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Old 10-04-13, 12:46 PM
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Thanks, You know what, I didn't see that little jumper between R and Rc. Called my wife at home to check, she said the jumper is there. pretty small, I missed it. Anyway, I am going to take off early Today and go home to try that 3 wires test. Now I am thinking that spare T-stat I have is from my old house, at least 12 years old, it is the old round type T-stat, may be it only needs 4 wires, so can I not to connect that C wire ? only connect R,W,Y,G ?
 
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Old 10-04-13, 03:05 PM
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OK, I connected those 3 wires together, everything up and running. So this means I have a bad thermostat ? If that is the case, Can I use that old 4-wire thermostat to replace the bad 5-wire thermostat ? at least for a few days until I get a new one. Thanks.
 
 

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