Discharging Run Capacitors - Or NOT to discharge? :)

I had a few people ask me about discharging the run capacitors on HVAC equipment. I finally got a few clips saved up so I could make a demo of that.

First things first, I do NOT manually discharge the run capacitors on HVAC equipment. The reason being... you don't have to! If the system has been operating normally, once you disconnect line power, the run capacitor(s) will be discharged in a matter of seconds through the motor windings still attached to it.

The only way to even leave voltage applied to a Run Capacitor is to disconnect a wire from it while it was running.

In the video I demonstrate that there is no voltage across the terminals within seconds of shutting off the main power. Then I do a demonstration by disconnecting the brown wire to the fan motor while it is running to leave voltage in the run cap. Then shut down the main power and short the run capacitor with a screwdriver.
It creates a few sparks :)
Note that the sound of the arch was so loud, that it caused the camera mic gain to be reduced for a few seconds before it increased enough again to pick up the surrounding noises.


The units used in the video are 3 phase 460 volts. The condenser fan motors are the only single phase motor in the unit therefore the only run capacitors as well. The Compressors and blower motor are 3 phase.

Category:

Howto & Style

Tags:

• hvac
• air
• conditioning
• conditioner
• trane
• run
• capacitor

[2Bibleppl]

Okay, I have one of those piece of junk Goodman heat pumps. We purchased it new and it was installed in 08' Every year we have a capacitor to go bad. The tech put a "hard start' in and it has just happened again. Last night when the unit tried to come on the lights dimmed severly several times in a row to the point that it really concerned me. Tomorrow the tech comes back to try to figure out what the problem is. Any advice would be greatly appreciated. Thank you for your time and trouble.

[hackfreehvac]

@2Bibleppl

Lights dimming for more than a split second definitely would indicate that the compressor is not starting right away or at all.

Make sure all the high voltage wires are tight at the disconnect and at your main breaker panel.

A voltage drop may add to the problem. But it probably would have smoked the breaker/disconnect terminals by now if it ran like that for more than a year or so.

[findvoltage]

hi again, i ment run-start capacitor, as a single unit. if it does exist can you give me an example how it works, i know that two metal foil sheets hold a charge and relese that charge, but a normal start cap would malfunction if i used it for a run CAP. so what is the difference between the two, thanks

[hackfreehvac]

@findvoltage

Start capacitors are quite higher in capacitance, which applied to the same motor winding as the run cap allows much more current flow than the lower microfarad run cap.

The start cap is also in a plastic enclosure which is not going to reject the heat well either.

However, they are only used MOMENTARY via a potential relay for extra starting torque of a motor.

The run caps are designed to be in the the entire time the motor is running.

[2Bibleppl]

@hackfreehvac

Thank you so much, the two tech guys are here now and have found exactly what you just mentioned. Last night we turned the system off and used an infared suntech space heater in one room, we didn't want to take the chance of a fire because the first time it happened we woke to a fire, bad news there [ but no injuries] Thank you so very much for sharing your knowledge with us. Take care.

[als3lo]

it is trane ac

مكيف ترين 20 طن

[hackfreehvac]

@Marzec309

I figured as much. :-)

[Marzec309]

@hackfreehvac Agreed, connecting a large dc cap as in car audio when its drained can easily blow 200amp fuses. Not to mention weld the wires to the terminal of the cap. Car audio caps are in the range of 0.5 farad to 20 farad and even larger. Starter and run caps used on motors are in the range of 0.000005 farad(5uF) to 0.000040 farad(40uF). They are significantly larger.

[findvoltage]

@hackfreehvac thank you for your time it is very much appreciated.

[ToledoApplianceGuys]

thats so true