Register to reply

Capacitor Fail

by russ_watters
Tags: capacitor, fail
Share this thread:
russ_watters
#1
May28-11, 09:05 AM
Mentor
P: 22,300
So the starter capacitor in my AC condenser exploded a couple of days ago. I'm headed out to get a new one (found someone open!) and I'm just concerned that the failure could be just a symptom of a bigger problem like a bad compressor or fan motor (its a dual capacity capacitor that serves both). I bought a new fan motor accidentally(?) because at first I thought that was the problem. It was dark out, the fan was hot and humming but not spinning and I didn't open the control panel to find the blown cap.

Here's the thing: when the cap exploded, I heard it and went outside. The fan was spinning slowly, but laboring and the compressor was running. It took a few minutes before the fan stopped spinning and I'm a little concerned that leaving it on for 15 minutes or so could have damaged the other components.

I have a service appointment for Tues, but with some parts in hand I may be able to fix it myself. What I don't want is to blow another cap because the fan motor really was the problem when I have a spare fan motor sitting in my basement. On the other hand, if I install the new fan motor unnecessarily, I won't get my $100 back. Maybe I'll buy two caps...

Suggestions?
Phys.Org News Partner Engineering news on Phys.org
DIY glove-based tutor indicates muscle-memory potential
Tricorder XPRIZE: 10 teams advance in global competition to develop consumer-focused diagnostic device
Study shows local seismic isolation and damping methods provide optimal protection for essential computing equipment
Dmytry
#2
May28-11, 09:29 AM
P: 505
I would compare old motor versus new using multimeter. I.e. winding resistance, winding to case resistance must be infinite, the motor must be possible to turn manually, etc.
Especially, check the winding that is powered through the capacitor.

It is really hard to give the advice without knowing the circuit. Especially as you say that capacitor serves both fan and compressor motors, which implies some really strange circuitry.
TurtleMeister
#3
May28-11, 10:10 AM
TurtleMeister's Avatar
P: 757
Quote Quote by Dmytry View Post
It is really hard to give the advice without knowing the circuit. Especially as you say that capacitor serves both fan and compressor motors, which implies some really strange circuitry.
A dual run capacitor is just two capacitors in one case.

The fan motor has a thermal overload located in the main winding of the motor. If the overload is working properly it will shut off current to the motor before damage is done. Odds are the motor itself is ok - if it was the capacitor that initially failed. According to Wikipedia, run capacitors now have a limited shelf life due to the EPA requirement that PCBs not be used in their construction.

Chunkysalsa
#4
May28-11, 10:59 AM
P: 311
Capacitor Fail

My dad runs an AC company and a blown capacitor is one of the most common problems.
russ_watters
#5
May28-11, 11:03 AM
Mentor
P: 22,300
Thanks guys. The cap was cheap so I bought 2.
Dmytry
#6
May28-11, 11:38 AM
P: 505
Quote Quote by TurtleMeister View Post
A dual run capacitor is just two capacitors in one case.
Ahh. I was thinking it actually shared capacitors between motors

The fan motor has a thermal overload located in the main winding of the motor. If the overload is working properly it will shut off current to the motor before damage is done. Odds are the motor itself is ok - if it was the capacitor that initially failed. According to Wikipedia, run capacitors now have a limited shelf life due to the EPA requirement that PCBs not be used in their construction.
Yep... well since he got a new motor anyway, he could check old motor against new motor with multimeter to make sure it's ok.... won't hurt to make sure.

I think you won't kill the capacitor... the worst that can happen to capacitor is that the winding powered through that capacitor is shorted out, which could overheat capacitor eventually.

What is the capacitance?
russ_watters
#7
May28-11, 12:33 PM
Mentor
P: 22,300
Quote Quote by Dmytry View Post
What is the capacitance?
35/5 uf. Here's a pic of the wiring diagram for those interested.

It's in and seems to be working. The service contractor wanted $108 just to diagnose it. The capacitor cost $9.50 (and I got a spare). Thanks for the help, guys.
Attached Thumbnails
Wiring Diagram1.jpg  


Register to reply

Related Discussions
Fail blog photos General Discussion 214
Capacitor - Resistor || Capacitor - Capacitor AC circuit Introductory Physics Homework 0
FBI Fail! General Discussion 19
What does it mean to fail? General Discussion 5
Trying not to Fail... General Discussion 0