Air handler fan runs continuously, possible FDR? w/pics

Old 06-21-07, 11:29 AM
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Air handler fan runs continuously, possible FDR? w/pics


My heat pump indoor air handling unit occasionally stays running after the compressor and outdoor unit shuts off. When this happens, it will not stop until the breaker is turned off.

I removed the thermostat from the wall mount (my thermostat is detachable digital model) while the fan was running, to test if it was the thermostat - the fan kept running indefinitely, even without the thermostat electrically attached.

So, I'm thinking it's a sticking relay of some sort, possibly a fan delay relay.

The Indoor unit is a Carrier and the following is printed on the air handler unit:
Model No. FC4BNF030000ABAA
Product No. FC4BNF030

I removed the cover from the air handler unit to inspect, and I see that it has two possibilities.

Firstly is a circuit board with what appears to be a small relay onboard. Here is a picture:


Secondy I see two black relay-like items mounted on a separate plate which appear to be inline with the blower - one is labeled "Therm-o-disc":

For more context and more pictures, check out:

So, my questions:
1. Does this sound like a failed/failing relay? Where is it located?
2. Where might I purchase a replacement?

Thanks in advance,

Last edited by DragonWyatt; 06-21-07 at 11:47 AM. Reason: Completed post, inadvertently pressed 'save' too soon
Old 06-21-07, 12:49 PM
Ed Imeduc's Avatar
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Id say get a new fan control center. Robertshaw makes one for a OEM replacement for the Carrier. might try Johnstone Supply. If you can buy there
Old 06-21-07, 05:55 PM
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Fan relay on circuit board

maybe the problem. That black thing in the bottom right of the ciruit board maybe keepng the power on the fan motor until you kill all power.

You have a black lead connected to normally open (NO) and a blue lead from the electric heat package connected to normally closed (NC), but I see (the bottom) the blue wire means you are running the fan on medium speed.

Blue wire on NC comes from electric heat to make sure the fan is running whenever the electric heat is on.

Kill all power to the unit and take the blue wire off the NC terminal and see what happens.

Carrier part number for this board is CESO130003-01.

Need model number from electric heat package to get part numbers for "that" heater.

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