AC fan motor won't spin without a push

[Brad54]

Got home tonight and the fan on the outside unit of the HVAC system wasn't spinning. Could hear everything humming, and what sounds like a high pressure line squealing, but no fan running.
It was 91 degrees inside the house. Hotter inside than outside at that point.

Checked the breakers, then went and stuck a long screwdriver through the fan guard and gave the fan a little push... it started spinning right away, got up to full-speed almost immediately, and ran enough to drop the temp down to 86 degrees.

Heard the high squealing/purging noise again, went and looked and the fan had stopped spinning. Gave it a shove with the screwdriver, got going again up to full speed in seconds.

I know if I call an HVAC guy, he's going to tell me I need an entirely new unit.

I'm thinking I just need a new motor.

Can anybody tell me why the motor isn't spinning anymore, and if replacing it will most likely be the fix for the AC system?

-Brad

 

[firworks]

You probably don't need a new motor. You probably need a new Start and or Run capacitor depending on your particular motor. They're pretty easy to buy and replace. Can you get a picture of the unit? Are there any access panels to get at the guts? Also you probably want to go hit the breaker in the house before getting all up in there unless you realllly trust your thermostat.

 

[BillK]

I know if I call an HVAC guy, he's going to tell me I need an entirely new unit.

That's a sad way to have to think of it.

 

[stimpy]

always kill the breaker before opening up a 240V unit and discharge the cap before touching anythign in there . as if the cap is good its discharge can kill you . have heard of several instances were people assumed it was a bad cap and it wasn't .

 

[Brad54]

Breakers I'm VERY familiar with, and never ever ever go in to anything when there's power to it.

Capacitors? Not so much.

 

[Ohmthis]

Brad, do you have meter? Most digital meters have a capacitance setting. Shut off power and wait 15-20 min to let the capacitor discharge. Mark and take the wires off. Set your meter to capacitance, place one lead on the c and the other on each terminal (assuming it's a dual cap). If it's out of range replace. There should be a size on the side of the capacitor.

 

[Rookie2]

google run capacitors. there are single units and dual, a/c suppliers won't sell to you unless you have an account.

 

[DC73]

You may not even need to test the capacitor. They tend to swell up when they fail, especially when they fail during the heat of summer. If the capacitor's case is bulging, it's a safe bet it needs to be replaced.

DC

 

[Rookie2]

you may be able to talk an a/c guy into selling it to you (they will bang you list or double ,I've paid $4cost to $15 2x list .
http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/

 

[Trey T]

Shops around Houston will sell to non-hvac contractor. Just check around your area

 

[crabjoe]

Grainger will sell retail too.

As for checking the cap, make your your meter can read farads. Also remove the wires before checking.

If you have Amazon Prime, you should be able to get one in 2 days. Depending on where you live, sometimes it's same day with Amazon Prime.

BTW, if you don't have a meter that can check capacitance, you might want to look into getting a Uni-T UT210E. It's under $40 on Amazon and it's a AC/DC True RMS clamp meter that can check capacitors too. The only things I wish this little meter had was in-rush and be able to read amps to 200 minimum... It does read to 100 amps which is more than enough to check running amps.

 

[Brad54]

I just went to Youtube and saw a couple videos on changing the run capacitor. Definitely something I can handle. (I installed retrofit motor control units on injection molding machines for about 9 months after graduating from college... Not the same thing, but at least I know how to deal with wires and electricity...)

I had a Grainger account about a decade ago and have bought from them. There's one close to me. I'll get into the unit tomorrow and see if there's obvious signs of the capacitor failing--leaking, bulging, etc. Hopefully there is, because I doubt I'll be able to test it.

I've got a good Snap-on multimeter, but my skill with it is limited to checking voltage, and checking continuity.

The motor runs strong and smooth once it's going. Doesn't have any noise like a bearing going bad, fan doesn't wobble at all like a bad bearing or worn shaft, and no obvious failures or anything going bad, at least on the top and sides of the motor where I can see it.

-Brad

 

[dogdad]

What's the difference between a "motor run" and a "motor start" capacitor?

 

[dogdog]

When my parent's unit went, I got their capacitors from this guy.... still running strong capacitor wise.... couldn't say the same thing for the Unit it self...

http://www.temcoindustrialpower.com/product_selection.html?p=start_capacitor_selection_guide

Good quality and price caps but COO might not digest too well with some....

 

[Ohmthis]

What's the difference between a "motor run" and a "motor start" capacitor?

Pretty much what it says. In a start capacitor motor there is a switch (usually centrifugal) that takes the boosting power of the capacitor out of the circuit when it is up to speed. On a run capacitor motor the capacitor is in the circuit the whole time it is running.

 

[Brad54]

Blowin' Cold!
Thanks guys. I couldn't have done this without you.
Ordered a new one from Granger, but it wouldn't be in until tomorrow. Drove to the plumbing and electrical supply house the next town over, and got the last one they had in stock--it had just come in that morning and wasn't even on the shelf yet.

It's a larger diameter than the one that was in it, but the bracket that held the old one in had been bent to be shorter and had a new fastener hole drilled in it. I unbent it, used the original hole and it was made for this diameter capacitor.

$25, 10 minutes to install.

I took the time to vacuum the dust, lint and... mystery fur off the condensor fins too. The back side was uniformly covered like the lint trap in my clothes drier, while the other three sides were about 80 covered but with a thinner layer.

Just one of those things I always meant to get around to, but never did.

Should help the machine work easier.

One last question: with the unit in the attic still doing its job, the outside unit got really hot; there isn't an over-pressure purge valve or anything, is there? Just wondering if I need to have the coolant topped off, since now that I know there was a problem, going back and thinking about it, this problem has been going on for a while.

-Brad

 

[brewchief]

Refrigerant levels shouldn't have been affected at all, there is an internal bypass that was probably opening. Water works best for cleaning the coil, hose pressure only, no power washers.

Sent from my XT1254 using Tapatalk

 

[theoldwizard1]

He is talking about the cooling FAN mounted above the compressor. It is small enough, it might not have any capacitors !!

• Kill the power to the unit
• Remove the top grate.
• Spin the fan by hand. Does it spin freely ? Any noise ?
• Add a few drops of light oil along the shaft where it enters the motor housing.

The cooling fan should be preety cheap and easy enough to install your self.

I had the same problem. Overheated the compressor and ... new A/C unit !

 

[DC73]

Just wondering if I need to have the coolant topped off, since now that I know there was a problem, going back and thinking about it, this problem has been going on for a while.

-Brad

If you have an infrared thermometer, you can do a quick test. When the unit is running and blowing cold air, measure the air temp coming out of a supply vent near the unit. Then measure the temperature at the return air grille. If you have a 17 to 20 degree differential between the two readings, the refrigerant level should be fine.

DC

 

[Brad54]

Don't have an infrared thermometer. Should probably be on my list of "things to get for the race car." Along with "Digital protractor."

Sadly, they are still on the Wish List.

-Brad