Capacitors in A/C unit question

[Jim Stabe]

I have an old Night & Day 5 ton A/C unit and I believe the run capacitors are weak. I want to replace them but I cannot read the size markings on them. I also cannot read the model # of the A/C unit anymore so I can't call the factory. These are pretty big capacitors - about 7-8" long. Is there any way to determine the value of the capacitors by the case size?

 

[MikeLawrence]

No, but a multimeter should work.

Michael Lawrence, Lissco
www.thruwalls.com

NOTE: If there are three poles then the capacitor is a dual and you'll have to measure both sides.

 

[rickairmedic]

Jim can you get us a picture of the capacitor . On a 5 ton you are most likely going to be in the 50-60 MFD area . You can also get the make and model number off of the compressor and that should help a supply house to tell you what size capacitor you should have .


Rick

 

[Eggman]

1. Pull the disconnect on the unit (disconnecting all power from the condensing unit).
2. Look down inside the unit at the top of the compressor.
3. Write down the Brand, Model # and Serial # of the compressor.
4. Write down the model number and the serial # of the condensing unit itself.
5. Call a local hvac parts house and give them the information. They can look it up in their parts books and tell you what they are.

Then to check if they are weak or not:
1. Pull the disconnect on the unit (disconnecting all power from the condensing unit).
2. Remove the side cover plate just above where the power whip goes into the unit.
3. Disconnect the wires from the capacitors (take a picture in high definition for later reference)

DO NOT CROSS/SHORT THE TERMINALS ON THE CAPACITORS, YOU WILL SEE A VERY BRIGHT FLASH

4. Taking a muiltimeter, set it on uf (micro farads), take black lead and place it on one terminal, and the red one on the other terminal. (do this for each capacitor).
5. The reading from the meter should be within + or -10% of the number from the parts house.
6. Re-attach the wires per the picture, push the disconnect back in fully.

HTH,

Eggman

 

[Jim Stabe]

I'll take a look tonight when I get home and let you know what I find.

Thanks

 

[oldgoaly]

Jim
How old is the unit? some of the newer non-pcb capacitors are much smaller in size than older capacitors. Should be able to cross-reference the compressor numbers to find the suggested capacitor. tt

 

[Jim Stabe]

Jim
How old is the unit? some of the newer non-pcb capacitors are much smaller in size than older capacitors. Should be able to cross-reference the compressor numbers to find the suggested capacitor. tt

That's part of the problem, I can't read any of the numbers on the old capacitors

 

[harvero]

1.

Then to check if they are weak or not:
1. Pull the disconnect on the unit (disconnecting all power from the condensing unit).
2. Remove the side cover plate just above where the power whip goes into the unit.
3. Disconnect the wires from the capacitors (take a picture in high definition for later reference)

DO NOT CROSS/SHORT THE TERMINALS ON THE CAPACITORS, YOU WILL SEE A VERY BRIGHT FLASH

4. Taking a muiltimeter, set it on uf (micro farads), take black lead and place it on one terminal, and the red one on the other terminal. (do this for each capacitor).
5. The reading from the meter should be within + or -10% of the number from the parts house.
6. Re-attach the wires per the picture, push the disconnect back in fully.

HTH,

Eggman

How does that work if the cap weak or bad, then the capacitance of the device must be reduced or gone? Caps can short or open, but the electric motor caps I have replaced were always open or very weak.

 

[Eggman]

With the meter on microfarads, and each lead on a different terminal, the meter will tell you if its good, weak, or bad. For instance, if the capacitor is a 35 uf (microfarad) and when tested, it measures at 30 uf. It is outside of the limits for being good. + or - 10% would give you a range from 38.5 to 31.5 microfarads. Being at 30 uf, its weak, get a new one. The same goes when its at 39 or greater, its above the limits and weak as well. Many times they will read low on an older unit, thus using more energy/power than what it should be when its running. If it reads 0 (zero), then its obviously bad. Replace it. Will they still work slightly above and slightly below the limits, sure. But a low or high reading capacitor will cause a higher amp draw which may result in a compressor burnout over time if its not corrected soner than later.

HTH,

Eggman