Replacing AC Capacitor

[grumpy0374]

AC working one day and not the next. Fan and heat strip work as they should, but ac compressor won't cut in.
Checked on roof, found ac start capacitor had a bit of oil residue.
Ordered new capacitor for both to be on safe side. This is for a 7 year old Dometic Penguin 2 unit'
Question concerns "shorting" the capacitor to remove. Everything I have read states to "short" the capacitor with a screwdriver to discharge it. But when one does this will there be any indication, like "sparking" to let one know that it is discharged?
All power was cut to rig, ac breaker off, and transfer switch off. When I crossed the tabs on capacitors nothing happened, so I'm just wondering if they are truly "discharged" before I handle them.
I do all my own maintaince, but have never run across replacing capacitor, and just want to be on the safe side.
Grumpy

[valleyduo]

Originally Posted by grumpy0374

AC working one day and not the next. Fan and heat strip work as they should, but ac compressor won't cut in.
Checked on roof, found ac start capacitor had a bit of oil residue.
Ordered new capacitor for both to be on safe side. This is for a 7 year old Dometic Penguin 2 unit'
Question concerns "shorting" the capacitor to remove. Everything I have read states to "short" the capacitor with a screwdriver to discharge it. But when one does this will there be any indication, like "sparking" to let one know that it is discharged?
All power was cut to rig, ac breaker off, and transfer switch off. When I crossed the tabs on capacitors nothing happened, so I'm just wondering if they are truly "discharged" before I handle them.
I do all my own maintaince, but have never run across replacing capacitor, and just want to be on the safe side.
Grumpy

Capacitors work like batteries to a point but most lack the ability to store power long term. They were likely discharged before you were tinkering with them.

[grumpy0374]

Thanks.
Going to be careful when removing them, rubber handle screwdriver, rubber handle long nose pliers to hold them.
Had visions of the cartoon character getting "zapped" .
Grumpy

[valleyduo]

Safety first always. I always double check with a volt meter before working on anything like that.

[johnbryanpeters]

Electrical engineer here.

Yes, short the capacitor after turning off power. It may or may not spark depending on charge state.

[grumpy0374]

I agree, but to check them, you have to remove the wires, and handle the capacitor. Everything I've read says do not handle unless discharged first.
Kind of like what comes first, the chicken or the egg. What to do first, handle and check with a meter, or discharge and than handle to check with a meter. The compartment where their located is small, and hard to connect meter without removing the capacitor.
Just don't want to handle if their still holding a charge.
Grumpy

[grumpy0374]

Originally Posted by johnbryanpeters

Electrical engineer here.

Yes, short the capacitor after turning off power. It may or may not spark depending on charge state.

Thank you sir...was hoping to get a someone with an electrical backround.
New capacitors delivered today.
Grumpy

[Bama Rambler]

There are several reasons that the cap may already be discharged when you go to remove it. The failure could be a short and that will discharge it. Sometimes the circuit that it's tied into will discharge it over time. Also some caps come with discharge resistors so over a period of time they will discharge the cap once power is removed.

Once you short the terminals with your favorite device (screwdriver, etc.), even if you don't get a spark, the cap is discharged. I usually short them a couple of times just to be sure.

[grumpy0374]

Thanks for the input everyone. Hoping it is just the capacitor. Everything else controlled by thermostat works, fan, heat strip, furnace. Just ac compressor won't kick on.
Here's hoping an 80 buck fix will do it, rather than a new ac unit.
Grumpy

[cavie]

Throwing a charged cap to your buddy in the electronics class was a favorite past time. Yes short before removing. It won't hurt you but it will make you hurt yourself if you don't discharge it. Sometimes sparks sometimes not.

[Iwannacamp]

I am not an electrical engineer. I claim no great knowledge...except cussing and eating. The official manual says to discharge the capacitor with and analog OHM meter. As the story goes.... you can damage the cap by shoring it...IE diode or something.

FWIW. Disconnect the shore power and turn off main breaker. The shock from the stored capacitor will not kill you. My experience is 30+ years HVAC service.

[rockfordroo]

Originally Posted by Iwannacamp

I am not an electrical engineer. I claim no great knowledge...except cussing and eating. The official manual says to discharge the capacitor with and analog OHM meter. As the story goes.... you can damage the cap by shoring it...IE diode or something.

FWIW. Disconnect the shore power and turn off main breaker. The shock from the stored capacitor will not kill you. My experience is 30+ years HVAC service.

He's replacing the cap anyway, so who cares?

Navy electrician here. Never heard of shorting a cap will damage it. TV repairmen (when we used to have them) used to do it all the time.

[Iwannacamp]

Originally Posted by rockfordroo

He's replacing the cap anyway, so who cares?

Navy electrician here. Never heard of shorting a cap will damage it. TV repairmen (when we used to have them) used to do it all the time.

Not always replacing.

Both right?
https://www.marsdelivers.com/wps/wcm...34cae8-mltrC81

You know what they say about... we always did it that way.

[SecretSquirrel]

It's not the shock from a charged cap the hurts so much (obviously there are some out there that can, before someone goes off on that) but the reaction to it. i.e. Falling off the roof.