Connection from A/C unit to transformer

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  #1  
Old 06-17-03, 09:30 PM
PReeves
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Connection from A/C unit to transformer

I have a 9-yr old Comfortmaker central a/c unit. This past winter I changed out the transformer (in my case, a fan control center) in my furnace and thought I duplicated all the thermostat and a/c connections exactly, but maybe not. When I switched the thermostat to cool nothing happened and it burnt up the fan control center (i.e. no a/c, no heat and no furnace blower with the thermostat turned to "fan on"). I've just replaced the fan control center again.

I have two wires (basically thermostat wires) from the central a/c unit to the fan control center. One is connected to the yellow thermostat wire (cool) and the other is connected to a common connection on the fan control center. Does this sound correct?

Now, when I turn the thermostat to cool, there is a humming noise in the fan control center. Is that normal? I've only left it on for a couple seconds because I'm afraid I'll burn up the fan control center again. The a/c does not come on immediately, but I've read where the a/c fan may take about 20 seconds.
 
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  #2  
Old 06-18-03, 09:20 AM
Ed G
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It sounds like you have it wired correctly, but you seem to have a short between your yellow and common for the condensing unit. I would disconnect the two wires going to the condenser and ohm them out. It could be your contactor coil is shorted or the wires are nicked and touching. Why did you have to change the transformer in the first place? Did you find out why it shorted?
 
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Old 06-18-03, 10:57 AM
PReeves
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I changed the transformer in January after I re-lit the pilot light but forgot to replace the access cover and burned up the wiring. All wiring and transformer was replaced at that time. I have replaced the two wires between the condenser and transformer so I don't believe they are touching. When I disconnect the wires from the condenser and check the ohms, is there a particular reading I should be looking for?

Thanks for your reply.
 
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Old 06-18-03, 11:41 AM
Ed G
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Depends on the type of meter you use, you should get the resistance of the contactor coil. You could disconect the same wires at the CU and make sure you have no continuity. If when you ohm the the line out you get an open circuit it just means a safety is open, could be a time delay relay.
 
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Old 06-18-03, 12:55 PM
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A/C

????????????? on that last note. When you pulled the 2 wires off the transformer to the condenser.You did put them back the right way???? If not you can feed the leg down from the tstat and short it out that way????Not there just kicking it around ED
 
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Old 06-18-03, 01:13 PM
PReeves
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I've tried it both ways I thought it could be:

Red wire from condenser to yellow thermostat wire connection at transformer and white wire from condenser to common connection at transformer and vice versa.

Both result in a humming noise on transformer (and hot to the touch very quickly) but no immediate movement of a/c fan blades.

Could it be that either the red or white needs to go to some other connection on the transformer rather than the common connection? There are three other connections besides the yellow from the thermostat to the transformer i.e. green (furnace blower), white (heat), red (power? to heat & cool on thermostat).

Thanks for your help.
 
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Old 06-18-03, 06:36 PM
PReeves1
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I checked the ohms between the two a/c wires disconnected from the fan center using a Fluke 336 clampmeter. There was a tone and a reading of 1.0. The access panel on the a/c unit reads:

Model ACS036A2C1
Model FBA036GC1
Serial# L9724 35362
Mfr # NACS036A2C1
Rated voltage 208/230 PH1
Max fuse or ckt: BKR (HACR type in USA)
Min. Circuit Capacity: 19.3

Compressor HP: ---
Compressor PH: 1
Compressor FLA: ---
Compressor RLA: 14.4
Compressor LRA: 82
Fan HP: 1/5
Fan PH: 1
Fan FLA: 1.3
Fan RLA: ---
Fan RLA: 2.30

Hope this helps you help me. It's getting hot!
 
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Old 06-18-03, 08:36 PM
Ed G
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Ok after re-reading my last post it seems to make no sense, and I know what I was trying to say. Anyway. What you should do is take the thermostat wire from the transformer to the cond. unit and disconect it at the transformer and at the cond. unit. All wires should be free and not touching. Check all wires for continutity to each other. You should have none. If say the red and white, while disconected show continuity than you have a short, which will short out the hot and common of the transformer.

If you prove the wires to be free of shorts, than you must have it wired incorrectly.
 
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Old 06-19-03, 03:58 AM
PReeves1
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I disconnected both wires from the transformer and a/c unit. There is no continuity. Is it possible that it is normal for the a/c fan blades to not move immediately and for the transformer to hum as it is. Am I just not letting it go long enough to start?
 
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Old 06-19-03, 01:11 PM
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AC wire

IF you want just take the 2 wires that go to the outdoor unit and thats all no other wires on the transformer put them on the transformer and see if this will start the outdoor unit or not. Dont let it run long this way just want to find out if the wire and the relay there work. You can look and see if you have a time delay there also ED
 
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Old 06-19-03, 01:17 PM
PReeves
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I'll try that. Let me run this past you. I've been saying I have the white wire from the outdoor unit going to the "common" connection on the transformer because that connection is labeled "C". I'm now wondering if that is the cool power connection. I've wired my new thermostat like the old one I had when I replaced it this winter, with the Rh and Rc terminals jumpered at the thermostat. Right now, there is no wire from the thermostat to the "C" connection on the transformer. I do have a fifth thermostat wire (a blue one) that is not being used. Could it be that I need that blue wire to connect to Rc on the thermostat and to "C" on the transformer? That way, I would have the blue thermostat wire connected to the white wire going to the outdoor unit and the yellow thermostat wire connected to the red wire going to the outdoor unit. What do you think?
 
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Old 06-19-03, 02:31 PM
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C is common, RC and RH should be jumpered unless there is a transformer in the outdoor unit. C is not always hooked up at the tstat, many do not use it. when cooling is called for, power (24V from transformer, R terminal on fan center) is sent back from the tstat on Y, which either ties directly to one of the outdoor low voltage wires in a nut, or at the circuit board depending on the model. (if at the circuit board,this will also energize fan in HI) then outside to the contactor,possibly through a safety such as a floatswitch in a pump, or float switch in a pan, follow the wire physically. often times the low voltage signal will run through a time delay (which may be bad) or a low pressure switch (which would hold unit out if refrigerant is low) then the voltage goes to the contactor, pulling in the points , then back to C at the fan center. get a meter if you do not have one, and let's see where we are losing voltage.

forget the circuit board info....you have a fan center....
no board

burning out the fan center tells us there is a short, this would be in a load, not a switch.....

my best guess is the fan control......

remove the wires from the contactor and try it, will rule out a shorted coil on the outdoor contactor.

the fact you replaced the fan center leads me to believe the problem is there

does the fan work in the on position?

put a fuse in line on the R wire (3 amp), save your self some bucks

may have to get a tech out there.
 
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