Diagnosing electric components in an air handler - help needed!

Old 07-11-11, 03:14 PM
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Exclamation Diagnosing electric components in an air handler - help needed!

Our 6 yr. old Carrier system has been fabulous until yesterday when the air handler stopped blowing. I opened it up and found no problem w/the cooling side - freon flowed and chilled the evaporator nicely. So that told me we're good on the compressor end.

I thought the capacitor might be bad and put a new one in, but nothing changed. Since I'm beginning to run out of potentially bad parts, my guess is that it's the relay, but don't know. There's no float control that I'm aware of.

How can I figure out if it's the motor, relay(board), or transformer? I'm into it this far, so I'd like to fix it myself!

Thanks guys!
Old 07-12-11, 07:09 AM
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First you need a multimeter and basic electrical knowledge. Can u take a picture of the schematic. Is there a call for cooling? breaker?
Old 07-12-11, 05:49 PM
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Carrier air handlers usually have a simple circuit board with a blue wire from the fan connected to a normally open (NO) terminal.

To prove motor operation, I would turn off the breaker(s) to the air handler, unplug the blue fan wire from the NO terminal and plug it into the incoming power terminal (highlighted yellow in this example) along with the heavy black wire located there.

Y connectors are available at Radioshack.

As Broods has posted, basic electrical knowledge is required.

What is the air handler model number?
Old 07-14-11, 06:10 AM
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Unhappy Totally perplexed!

Thanks guys.

I went through a process of elimination and came up with the relay or relay board being the likely problem. Jumping the blue motor wire from the main feed, the fan runs. Disconnecting the capacitor and trying again, the motor wouldn't start, reconnecting again, it did - indicating a good cap. Voltage into the transformer: 230, output: 28. So to me, all that's left is a bad relay. However, I just installed a brand new HK61EA006 relay board and it didn't fix anything.

Here's the twist:
I have the relay carefully bi-passed w/a jumper wire from the main feed to the motor wire and the system works fine. In fact, the A/C unit itself responds to the thermostat and cycles on and off as expected. I find it hard to believe that the new board (purchased on-line) is bad, but I guess it's possible.
I must be missing something in my troubleshooting but don't know what! What can it be?
Old 07-15-11, 05:43 PM
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ensure the new board is wired correctly and that the blue wire you speak of is on the correct terminal on the control board or relay.

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