Where is transformer?

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Old 07-19-19, 04:20 PM
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Where is transformer?

Google search says either in the furnace or outdoor condenser. Furnace is Carrier Infinity and condenser is Carrier XL 12. Thank you.

Problem is no power on the therrmostat red wire. I got a wifi thermostat that ran a month and now the error message. Google search shows these wifi thermostats draw higher current than the non-wifi verion. I am suspecting a burnt out transforer. Thank you.
 
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Old 07-19-19, 05:04 PM
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Transformer is in the furnace control panel. You also have a 3 amp fuse that is plugged into the circuit board. Look at the fuse first. Make sure you install the blower door panel correctly, there is an interlock switch that needs to be engaged.
 
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Old 07-19-19, 07:43 PM
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Thank you, 57TinkerMan. Exactly as you said, the fuse was blown. That fuse protected everything. Replaced it, and put the old thermostat back. All is working well.
 
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Old 07-19-19, 09:12 PM
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That is very strange. There may be a higher load than normal on that three amp fuse causing it to blow with the wifi stat. The only way to know for sure is to measure the current draw thru the R (red) wire.
 
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Old 07-20-19, 11:09 AM
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I just talked to google about their Nest thermostat. They said it draws only 100-200 mA of current. I cannot see how this little current can blow a 3A fuse.

Assuming 24V transformer triggers AC (or heater) contactor and blower contactor, when both get turned on at the same time, they will draw about 2A. 3A seems to be too close to actual current. Can I up it to 4A?

A related question. As a contactor gets old in age, will it draw more current?
 
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Old 07-20-19, 11:33 AM
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Hi, if the 3 Amp was the original then thats what should be there. Check the wiring Dia. to be sure.
Geo
 
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Old 07-20-19, 12:15 PM
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OK, I will keep the OEM fuse rating. AC is running well so far. Initially I was suspecting the wifi thermostat drawing excessive current. I am not sure any more. As you suggested, I need to check ohms between wires and contactor coils. Thank you.
 
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