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Old 11-29-2012, 03:19 PM   #1
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Need help testing RTU transformer (Pics)


Hi there,

The problem: I have no power to a 1H/1C thermostat. I have checked the whole wire for a splice, short, etc and the wire is good. I have tested power with a multimeter to the red power connection and the green blower connection, and have manually spliced the power and blower wires to at least kick on the fan. Even with it spliced, it will not turn on the fan - The unit will not kick on.

What I have done: I have tested power on the roof top unit (It is a small carrier model) from the power in to the contactor and I get 120v on both sides of the contactor. In addition, I can manually kick on the compressor on this contactor (not going to do me much good as it is -22 celcius out). What I wanted to do was test the high and low side of the 24v transformer, which usually is not hard for me to do on the Lennox models we have here (90% are Lennox) but I'm unsure about this carrier, as it is different.

The carrier model is a 48-SS 1 heat 1 cool. Link HERE

If I understand correctly, there is a fault LED (seen in one of the pictures) - There is no flashes, but I am not sure if I have to manually start that LED somehow to test that.

What I need an answer to:
  1. Am I correct in starting my search at the transformer?
  2. Based on the pictures below... What the heck do I do???
Thanks guys!

Cam







Last edited by CamaLamaDD; 11-30-2012 at 10:33 AM. Reason: Solved problem
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Old 11-29-2012, 05:55 PM   #2
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Need help testing RTU transformer (Pics)


Check for 24 volts at R and C on the board.

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Old 11-29-2012, 09:06 PM   #3
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Need help testing RTU transformer (Pics)


Quote:
Originally Posted by CamaLamaDD View Post
Hi there,

The problem: I have no power to a 1H/1C thermostat. I have checked the whole wire for a splice, short, etc and the wire is good. I have tested power with a multimeter to the red power connection and the green blower connection, and have manually spliced the power and blower wires to at least kick on the fan. Even with it spliced, it will not turn on the fan - The unit will not kick on.

What I have done: I have tested power on the roof top unit (It is a small carrier model) from the power in to the contactor and I get 120v on both sides of the contactor. In addition, I can manually kick on the compressor on this contactor (not going to do me much good as it is -22 celcius out). What I wanted to do was test the high and low side of the 24v transformer, which usually is not hard for me to do on the Lennox models we have here (90% are Lennox) but I'm unsure about this carrier, as it is different.

The carrier model is a 48-SS 1 heat 1 cool. Link HERE

If I understand correctly, there is a fault LED (seen in one of the pictures) - There is no flashes, but I am not sure if I have to manually start that LED somehow to test that.

What I need an answer to:
  1. Am I correct in starting my search at the transformer?
  2. Based on the pictures below... What the heck do I do???
Thanks guys!

Cam





yes check for 120 volt going to transformer supply side then check for 24 volts on secondary side.... if you have the proper voltage on both sides of transformer..check for inline fuses..ben sr
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Old 11-30-2012, 10:31 AM   #4
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Need help testing RTU transformer (Pics)


Turns out it was a fuse, I must have shorted the red wire when I took the thermostat off the other day. Thanks Ben.
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