Tuesday 2 February 2021

Carrier FA4CNF024 Intermittent Blower Fails to Start

Hello All,

I have a Carrier FA4CNF024 where the blower motor intermittently fails to come on when called. It appears to be a bad connection, cold solder joint, sticking relay, etc because when this occurs I can smack the side of the unit and the blower immediately comes on. The issue appears to be related to the control board/wiring (as opposed to the blower motor itself) as I can open only the top panel and very lightly tap the wiring / control board (far from the blower itself) and the motor will start running. So far been I've been unsuccessful in troubleshooting the issue since even attempting to backprobe the connector at the board with my meter probe is enough to cause the blower to come on (this is how I discovered this behavior in the first place). I pulled the board and looked it over under magnification for cold solder joints, but everything looks. I may go over all joints on the board just to rule that out completely. I've also checked that all crimps look good and I've cleaned up all pins and connectors with a little file and put dielectric grease on all of the connections. Unfortunately the problem remains. One thing to note is that I have been unable to get the blower motor to STOP working from a running state by jiggling the same wires and tapping on the control board (this behavior makes me lean to a sticking relay on the board).

I can't stand throwing parts at an issues without proper troubleshooting and a real diagnosis, however I think I'm at the point where I don't have much choice and may try replacing the relays (or entire board - depending on price). However, before doing so I figured it would be worthwhile to get the thoughts of others. Who knows maybe this is a common issue with this unit that most pros have seen a hundred times?

Any thoughts or ideas are appreciated. Thank you. -Thomas


source https://hvac-talk.com/vbb/showthread.php?2226273-Carrier-FA4CNF024-Intermittent-Blower-Fails-to-Start&goto=newpost

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