blower fan doesnt start - Page 1
Forum section: electronics / repair

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 09:24:29 pm
content: I have an ac unit that works fine but the blower doesn't start spinning unless I spin it. I know this sounds like it would be a bad start capacitor but I checked what I believe to be the start capacitor and it is very close to its rating. once it spins up it also isn't as fast as it was originally. I'm not sure how this type of motors works exactly but could it be stuck in its start cycle so it wont spin up or the other way around. any suggestions will be taken its really humid and I need some cool air

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 09:32:55 pm
content: another note is the fan will not spin at all on low. I'm thinking its possibly the thermal cutoff is partially open or something so its passing some current but not enough to get it spinning. he motor also gets pretty warm as well

author: Gyro
author_rank: Super Contributor
timestamp: May 15, 2020, 09:37:21 pm
content: Is it a start capacitor or a run capacitor? What's the type and value / rating.Edit: Given that I'm off to a nice cool bed...It it is a start capacitor then it will be a short duty cycle bipolar electrolytic, switched out by a centrifugal switch on the motor armature. Motor run capacitors are Polypropylene film continuously rated ones (with just 3 wires coming out of the motor winding).Motor capacitors deteriorate over time - they may still show an approximately correct capacitance value but the ESR will have increased to the point where they just can't pass the current anymore. Given the low cost (and apparent desperation!), just change it. If it fixes the problem, you'll be happy. If not then you have a more complex problem that will be harder to find and fix anyway. Play the odds.

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 09:50:38 pm
content: im not sure if its a start or run, its a 2.2uf. its the top one in the pic

author: Gyro
author_rank: Super Contributor
timestamp: May 15, 2020, 09:56:42 pm
content: At that low value, it's a run capacitor. See my edit above.PS. That sounds like a very small cap for what sounds like quite a big fan, check around and make sure there isn't another bigger one connected to the motor windings (there looks like a bigger one underneath it). Change them both if it's a variable speed fan.

author: ArthurDent
author_rank: Super Contributor
timestamp: May 15, 2020, 09:57:06 pm
content: Have you checked to see if the bearings have run dry? The oil can dry out to a near varnish consistency. If you get the fan running and turn the AC off, does the fan stop fairly quickly or spin several seconds to a stop like it should. Just last night I had to re-oil the sleeve bearings in an portable fan.

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 10:20:39 pm
content: Quote from: ArthurDent on May 15, 2020, 09:57:06 pmI know you need an actual ESR meter to test it properly but if I measured it with a normal resistance meter what would I expect

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 10:21:31 pm
content: Quote from: ArthurDent on May 15, 2020, 09:57:06 pmwell when I spin it up if I spin it the wrong way and I turn it off it will spin for minutes

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 10:30:42 pm
content: would this be an appropriate capacitor replacement. the original is actually 2.5 uf and I have a 2.2uf

author: wilfred
author_rank: Super Contributor
timestamp: May 15, 2020, 11:12:30 pm
content: Quote from: CoopedUp on May 15, 2020, 09:32:55 pmThermal cutoffs don't partially open. They cutoff. I think you may have a winding that has burned out. I'd check for continuity on the coils. I'm assuming doesn't spin at all on low means it does on other speeds. And the comment "well when I spin it up if I spin it the wrong way and I turn it off it will spin for minutes " means the bearings and/or lubrication are OK.Trying a new capacitor is cheap and easy if you have a spare or can get one quickly. But it might be you need the smallest spare part that includes a new motor.I had a fan that showed similar symptoms including running warm and that is about the extent of my experience. I tried a new capacitor and it was ineffective. Hope you have better luck.

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 15, 2020, 11:22:56 pm
content: i tried a new cap and it didn't change anything. guess that means something else is up. ill try and get the motor out and open it up to further inspect

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 16, 2020, 12:27:01 am
content: i took the motor out and used it on its own, it seemed to work just fine... it started perfectly fine on high and medium but it wouldn't start itself on low. another thing is there is 4 settings for fan speed on the controller as in high med low and then none of the above which I assume that's off but it keeps spinning at full speed. could this be a problem?

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 16, 2020, 12:35:26 am
content: it's definitely the motor. I'm going to briefly glance at how much they cost and just buy a new ac unit