How to safely discharge a HVAC start/run capacitor?

[dmccarty]

We heat the house with a wood stove, but last week, when the temperatures were down in single digits and the highs were in the low/mid 20s, the wood stove could not keep up with the cold. That meant the living room was at 72 instead of 80 and the Wifey was not happy. :laughing: I wanted to kickup the heat in the house so I turned on the heat pump which ran for a few minutes and then made a rather scary loud noise. :shocked: I went out side and the fan had stopped running so we turned off the heat pump. Emergency heat works but the fan will not start. Last time this happened was during a heat streak where we had 100 plus temperatures for well over a week. The cause was a bad start/run capacitor. I looked at the capacitor and it is not bulging like the one during the high heat conditions.

I have the service manual and I want to test the capacitor but I need to safely discharge the capacitor. The manual says to discharge with a 20-30 ohm resistor. Is there another way?

I have read some information on the Internet on how to do this, but I trust the TBN Brain trust far more than some article written by who knows who posted on the Internet. :laughing::laughing::laughing:

I really don't want to get lit up by a capacitor the size of a beer can. :shocked::shocked::shocked:

Thanks,
Dan

 

[k0ua]

We heat the house with a wood stove, but last week, when the temperatures were down in single digits and the highs were in the low/mid 20s, the wood stove could not keep up with the cold. That meant the living room was at 72 instead of 80 and the Wifey was not happy. :laughing: I wanted to kickup the heat in the house so I turned on the heat pump which ran for a few minutes and then made a rather scary loud noise. :shocked: I went out side and the fan had stopped running so we turned off the heat pump. Emergency heat works but the fan will not start. Last time this happened was during a heat streak where we had 100 plus temperatures for well over a week. The cause was a bad start/run capacitor. I looked at the capacitor and it is not bulging like the one during the high heat conditions.

I have the service manual and I want to test the capacitor but I need to safely discharge the capacitor. The manual says to discharge with a 20-30 ohm resistor. Is there another way?

I have read some information on the Internet on how to do this, but I trust the TBN Brain trust far more than some article written by who knows who posted on the Internet. :laughing::laughing::laughing:

I really don't want to get lit up by a capacitor the size of a beer can. :shocked::shocked::shocked:

Thanks,
Dan

To be honest with you, I think the danger is not all that great. If concerned, measure for voltage with your VOM. I doubt there is any, but it won't hurt to find out.. If you do find several hundred volts. Then take a resistor with a good set of insulated pliers and put it across the terminals. It will fall in in hurry. I have just used a screwdriver too. Might not be as good for the cap, but I can't say that I have ruined any by using that method.. I have repaired and worked on electronics for around 50 years.. Including many lethal circuits. but a cap disconnected from a circuit never worried me all that much.

 

[Sprinklerman]

if the emergency heat was on , the fan outside wouldnt be running , its using resistance heat coil on the inside unit.

 

[kenmac]

Not sure the cap is your problem ,but ,I'll answer the question about the cap... I discharge mine with a screwdriver,etc, To test,,, set the volt meter to ohms scale. connect to the C and to fan terminal.. then move to the herm terminal Your meter will also discharge the cap.. It will charge it and discharge it.. To read what the cap is putting out, you need a cap tester

 

[Eric Salop]

There can be quite a high charge left on a capacitor if you happen to disconnect at the peak of the mains cycle.
It's often enough to give quite a loud crack when the screwdriver blade touches both terminals. It can certainly make you jump and may even erode away a bit of the capacitor terminal (and your screwdriver). It is the easiest way though.

Many homes do have a low value resistor that is capable of discharging very high currents - the heating element in an electric tea kettle (with the switch on).

One other point if you are checking with a voltmeter to see if a capacitor is charged :
Although in use the capacitor is on an ac supply, once you disconnect the supply you will need to set the voltmeter to read dc voltage to check for any remaining charge.

 

[Loadstar]

Like others say lay a screw driver on it. There are capacitors made in America that I suggest over china maypops. They are Titan HD capacitors. China capacitors are garbage.
Attached a photo of a nice capacitor blowout for your entertainment.

 

[Leejohn]

Just toss it to your 6'5", 300lbs older brother and run like h-----. Go ahead and call the heating man, a back hoe man because you might not have a heating system left when you get back.

 

[murphy1244]

Just toss it to your 6'5", 300lbs older brother and run like h-----. Go ahead and call the heating man, a back hoe man because you might not have a heating system left when you get back.

I was going to say that I'd just toss it to my partner and yell catch.

 

[antlers125]

Just curious, what type of Heat Pump do you have that works in single digit temps?

 

[dmccarty]

if the emergency heat was on , the fan outside wouldnt be running , its using resistance heat coil on the inside unit.

Correct, that is why we ran the Emergency heat. The sad thing was the Emergency heat did not raise the heat in the house very fast. I think we expected the heat to rise like it does with the wood stove. :confused3::laughing: This was the first time we have used the Emergency heat other than to test the system years ago.

Later,
Dan