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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22512
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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AC unit fan not kicking on?

Customer Question

AC unit fan not kicking on?
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.


Your issue will be likely be the defrost board. It controls the fan in winter...but it is responsible for ac in summer but no defrost. There is a test if you would like to do a hands on project..

Expert:  BillyHvac replied 1 year ago.

If you wish to proceed with the test just let me involves moving one wire

Customer: replied 1 year ago.
sec, typing atm. Thanks!
Expert:  BillyHvac replied 1 year ago.

Coming from the motor (if still color coded) is a purple wire that goes to a circuit board on a terminal you see this terminal?

Customer: replied 1 year ago.
Absolutely. Just to add since the initial "what have you done" field had a character limit here is the rest.We had a capacitor go out in the unit (45-5mfd) about a year or so ago and my father in law swapped it out for a 50-7.5. Didn't think it was a big deal since caps have a tolerance range and I'm used to working and swapping out components in TVs, motherboards, etc. May or may not be useful info.We swapped the fan motor and it did the exact same thing as the original -- has trouble kicking on but can be kickstarted to spin. So I swapped the capacitor with the spec'd one (45-5mfd). It kicked on once but didn't afterwards. I looked at the replacement motor specs and noticed the specs for running MFD were a little higher vs the original. Proceeding, I Installed the the original motor which matched the new capacitor's rating (5MFD) and it still will not kick on. When the compressor kicks on I can see the fan 'wobble', and if I kickstart the fan it engages and spins up. So based on these tests I assume both the motor and capacitor is OK.Will look at your previous comments and comment back. Thanks!
Expert:  BillyHvac replied 1 year ago.

on this unit there are few things that can cause this.

Capacitor - which you changed

Motor - which you changed

Defrost board - which is what I want to test.

Since you are tech savvy I assume you have a set of jumpers?

Customer: replied 1 year ago.
Purple from motor goes to this board. What do you need me to jump?
Expert:  BillyHvac replied 1 year ago.

At the bottom of board.

A purple comes from fan motor. DF2

A red comes from dual capacitor terminal C - DF1

We want to put a jumper on DF1 to Df2..then try unit.

Customer: replied 1 year ago.
Shorting DF1+DF2 made no difference. When the compressor kicks on see the fan "trying" to kick on but doesn't have enough juice to actually start it. The fan wobbles back and forth... initially from about .3cm and looked to gradually give to about 2cm clockwise to counter-clockwise but doesn't fully spin. Kickstarting it gets it going.
Expert:  BillyHvac replied 1 year ago.

Remove jumper.

Measure voltage as such -

one meter lead to DF2....other meter lead to contactor where black wire from motor attaches attaches.

Customer: replied 1 year ago.
One thing I will mention is I suspect a short somewhere but don't know how to diagnose it. When we were initially changing out the fan motor I noticed I slight charge on my hand when I touched the top of the fan assembly/circular protector. I was barefoot. Not sure if that helps. Will check voltages and post back. Thx
Expert:  BillyHvac replied 1 year ago.

also let me know if new motor wired te same or was a retrofit

Customer: replied 1 year ago.
243VAC on both DF1+DF2 to black. Original wiring is in place on original motor. Black+Purple+BROWN.
Expert:  BillyHvac replied 1 year ago.

And Brown is on Fan on dual capacitor?

Customer: replied 1 year ago.
Bingo!! (Hopefully!) The brown from the fan motor isn't connect to anything as the connector has broken off and was hanging freely in the mess of wires. Where do I hook it up?
Expert:  BillyHvac replied 1 year ago.

The brown wire goes to F (fan) on the dual capacitor

Customer: replied 1 year ago.
Strange. I had hooked up brown to the cap when I swapped it out. Apparently it broke in the processes. Tied it in temporarily and unit is booting up. Will post back.
Customer: replied 1 year ago.
First power on fan kicked on as needed. Will watch it for a bit and post back.
Expert:  BillyHvac replied 1 year ago.


Hope that is all it is. If it fires up and all is well just rate service and I will move off active list.

If you need more info just let me know.


Customer: replied 1 year ago.
Tested 3 more times and after getting the brown fan motor reconnected the fan kicked on as expected.For reference I'll give my piece...I think based on my tests it was in fact the capacitor that was bad all along. I believe during the cap switch the brown connector broke and caused the 45MFD not to fire on the motor which is why I saw the sub-par power to the motor but it wouldn't fully spin up unless kickstarted.Does this sound reasonable? Is the brown in fact the wire that handles startup (FAN on capacitor)?Awesome job helping me out man!! I'm going to leave this thread open for another 24hrs just to make sure we don't have any more issues but your help so far has been tremendous in diagnosing the [new] issue!! You definitely have a great review coming your way.
Customer: replied 1 year ago.
Bad news ugh.. After about an hour I walk out and the fan is not kicking on anymore. Its back to it's old ways.. when the compressor kicks on the fan hesitates and tries to spin up but doesn't fully get started. Kickstarting it gets it going. Need any additional readings?
Expert:  BillyHvac replied 1 year ago.

I would cut and crimp fresh fitting on brown wire and replace the capacitor (again).

There is a chance the cap or start windings have been compromised due to previous failed starts.

AND make sure the cap matches motor microfarad value.

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