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Discussion Starter · #1 · (Edited)
Are there any electricians out there? I salvaged(?) a dehumidifier that stopped working. I placed this thread in the ‘Tool” section because it is going to be used in a kiln if I can fix it. It’s fairly new but when it’s plugged in, it hums and then blows the circuit breaker. The compressor motor has a capacitor that I thought might have gone bad. Maybe the condenser’s motor bearings are locked up. Is there any way to check out a capacitor to see if it’s still good? I have more questions about the D/H in general, but I’ll take this one step at a time.

Thanks
 

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Caps are easy to test if you have a multimeter with the ability to measure capacitance. If you don't have one, you can always take the cap somewhere that does have one.
 

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Discussion Starter · #3 ·
Caps are easy to test if you have a multimeter with the ability to measure capacitance. If you don't have one, you can always take the cap somewhere that does have one.
I forgot to mention that I do have a meter; that was the whole point of this thread. How to test it is what has got me puzzled.
 

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djg said:
Are there any electricians out there? I salvaged(?) a dehumidifier that stopped working. I placed this thread in the ‘Tool” section because it is going to be used in a kiln if I can fix it. It’s fairly new but when it’s plugged in, it hums and then blows the circuit breaker. The compressor motor has a capacitor that I thought might have gone bad. Maybe the condenser’s motor bearings are locked up. Is there any way to check out a capacitor to see if it’s still good? I have more questions about the D/H in general, but I’ll take this one step at a time. Thanks
They are fairly easy to test with an old analog meter. First short out the two terminals to make sure it is discharged. Then with set the meter on the ohm scale put the leads on the capacitors terminals. You should see a complete circuit as the capacitor is charged by the ohm meters battery. As the capacitor is charged the ohm meter will go to infinity showing an open circuit. This will tell you the capacitor is not open or shorted. I used to do A/C work on the side and this procedure worked well for me. It is hard to do with a digital meter. Tom
 

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Discussion Starter · #5 ·
They are fairly easy to test with an old analog meter. First short out the two terminals to make sure it is discharged. Then with set the meter on the ohm scale put the leads on the capacitors terminals. You should see a complete circuit as the capacitor is charged by the ohm meters battery. As the capacitor is charged the ohm meter will go to infinity showing an open circuit. This will tell you the capacitor is not open or shorted. I used to do A/C work on the side and this procedure worked well for me. It is hard to do with a digital meter. Tom
I have an old analog VOM that I can did out. But as you can see from the photo, I have 3 terminals; 'Fan', 'Herm' and 'C'. Which is which?

The schematic lists them as 'S' (Start?), 'R' (Run?) and 'C' (Common?).
 

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puffessional Scrabbleist
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capacitance

This is a dual-cap and uses a common point (C) as the reference for both. It is possible to connect this up backwards and get bad results so be sure the polarity on the cap is followed. The C should be negative.


Anyone who works on old radios should have a capacitance checker on their bench. I have two if you are anywhere near Oregon but if you know anyone along this line in your area you might try them. For all intents and purposes the previously mentioned VOM method will tell you whether it is good or not.

These leak sometimes but in a new one it is almost unheard of. The two caps are not very close in size 4 vs 30 mfd) so if you had it reversed in that manner the smaller one would fill up quickly and possibly blow CKT BRKR.

The windings of the motor could have some problems. You said the bearings are frozen so I'm assuming it is frozen in place mechanically. Does it spin easily on the bench? Does it only lock up under power? It depends on how the thing is wired internally but an open winding on one side could cause it to lock up on the other side. The circuitry is looking for a varying impedance and with a stationary rotor it's constant.

I think you'll get your answer with the previous suggestions but if not you can look elsewhere with ease.
TonyM
 

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Discussion Starter · #7 ·
This is a dual-cap and uses a common point (C) as the reference for both. It is possible to connect this up backwards and get bad results so be sure the polarity on the cap is followed. The C should be negative.
So I check the resistance between C and Herm and then C and Fan. I should get some sort (Non Zero) of resistance reading?

Anyone who works on old radios should have a capacitance checker on their bench. I have two if you are anywhere near Oregon but if you know anyone along this line in your area you might try them. For all intents and purposes the previously mentioned VOM method will tell you whether it is good or not.

These leak sometimes but in a new one it is almost unheard of. The two caps are not very close in size 4 vs 30 mfd) so if you had it reversed in that manner the smaller one would fill up quickly and possibly blow CKT BRKR.
No visible External leaks. Maybe internal between the ....?
The tripping of the breaker occurred before I started to mess with the wiring. No chance of reversal.

The windings of the motor could have some problems. You said the bearings are frozen so I'm assuming it is frozen in place mechanically. Does it spin easily on the bench? Does it only lock up under power? It depends on how the thing is wired internally but an open winding on one side could cause it to lock up on the other side. The circuitry is looking for a varying impedance and with a stationary rotor it's constant.

I thought possibly the bearings were locked, hence the tripping. I have not removed the motor's housing yet. I thought I'd check the most obvious? thing first, the capacitor.

I think you'll get your answer with the previous suggestions but if not you can look elsewhere with ease.
TonyM
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djg said:
I have an old analog VOM that I can did out. But as you can see from the photo, I have 3 terminals; 'Fan', 'Herm' and 'C'. Which is which? The schematic lists them as 'S' (Start?), 'R' (Run?) and 'C' (Common?).
As Tonym said that's a dual capacitor. It is used for both the fan and compressor. To test the one for the compressor use the one labeled C and I don't remember from the drawing but the one NOT labeled fan. I believe it was labeled Herm.
Tom
 

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Discussion Starter · #9 ·
I found a video that explained what you were saying. Both capacitors appear to be fine. The question is can the motor/capacitor be now hooked to the lead of a power cord to see if the motor is any good?
 

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djg said:
I found a video that explained what you were saying. Both capacitors appear to be fine. The question is can the motor/capacitor be now hooked to the lead of a power cord to see if the motor is any good?
I though you had already tested it with everything hook up and suspected a bad capacitor.
Tom
 

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Caps are easy to test if you have a multimeter with the ability to measure capacitance. If you don't have one, you can always take the cap somewhere that does have one.
If he does not have a multi-meter, he can always charge it, leave it on the bench for a couple of minutes and then grab the terminals with both hands. The success will be directly proportional to the surprise. :shifty:
 

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Discussion Starter · #12 ·
I though you had already tested it with everything hook up and suspected a bad capacitor.
Tom
No, maybe I didn't make it clear. That was the point of this thread; I didn't know how to check it. Now that I know the capacitor is good, I need to check the motor.
 

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caps

If everything looks right and it still blows I'd suspect the two caps are wired wrong and the smaller cap is trying to do the job of the larger one and is charging too quickly. This can be incorrect and still have the ground reference correct. 30ufd is a big capacitor and is being used to start the motor. You can fudge on the specs a little but 4 for 30 will cause problems. The other is probably just a noise filter so it doesn't mess with the radio when it spins.

Good Luck
TonyM
 

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Discussion Starter · #14 ·
If everything looks right and it still blows I'd suspect the two caps are wired wrong and the smaller cap is trying to do the job of the larger one and is charging too quickly. This can be incorrect and still have the ground reference correct. 30ufd is a big capacitor and is being used to start the motor. You can fudge on the specs a little but 4 for 30 will cause problems. The other is probably just a noise filter so it doesn't mess with the radio when it spins.

Good Luck
TonyM
It blew the breaker before I even messed with the wiring. Impossible to have them crossed. What I want to do is hook the motor/capacitor up separate of any other garbage to see if the motor will run.
 

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djg said:
It blew the breaker before I even messed with the wiring. Impossible to have them crossed. What I want to do is hook the motor/capacitor up separate of any other garbage to see if the motor will run.
Use your meter to check the resistance of the motor windings. I would suspect one of the two is open or a stuck compressor. Measure the resistance between the common and the terminal the capacitor is connected to and between the common and the other terminal (run windings).
Tom
 

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TonyM said:
If everything looks right and it still blows I'd suspect the two caps are wired wrong and the smaller cap is trying to do the job of the larger one and is charging too quickly. This can be incorrect and still have the ground reference correct. 30ufd is a big capacitor and is being used to start the motor. You can fudge on the specs a little but 4 for 30 will cause problems. The other is probably just a noise filter so it doesn't mess with the radio when it spins. Good Luck TonyM
The 4ufd is connected to the fan.
Tom
 

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puffessional Scrabbleist
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windings

Looks like it is connected correctly. Sometimes motors get frozen in place if stored in a damp location. The high iron content will rust and create a "short" blowing the ckt brkr. Make sure the motor turns freely. You can pull it apart but it's not all that easy. It depends on the quality of the motor.

TonyM
 

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TonyM said:
Looks like it is connected correctly. Sometimes motors get frozen in place if stored in a damp location. The high iron content will rust and create a "short" blowing the ckt brkr. Make sure the motor turns freely. You can pull it apart but it's not all that easy. It depends on the quality of the motor. TonyM
Tony, it's basically a air condition compressor. It is hermetically sealed like a refrigerator compressor/motor. No way to try and turn it or disassemble it.
Tom
 

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Discussion Starter · #19 ·
Tony, it's basically a air condition compressor. It is hermetically sealed like a refrigerator compressor/motor. No way to try and turn it or disassemble it.
Tom
The D/H was being used on a daily basis when it went bad; not a storage issue. And yes it appears to be a sealed unit so I can't rotate the shaft (as you already stated).

I will take some readings today and get back to you.

Thanks Everyone
 

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unsure if the motor will run without hte pcb connections - doubt it. motor also appears to have multiple speeds, with hi and low switches feeding the connections. from what is shown, a switch controls the compressor, which may be stuck on. a motor will have difficulty starting under load and will trip breaker.
 
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