Need help with motor on compressor

ldj · Jan 18, 2015

Yesterday my compressor wouldn't start, it just hummed. I gave it a little turn with hand and it took off. It started several times while it was using it. Today it won't start even giving it a little turn. I'm wondering about start capacitor. There are 2 capacitors on top of motor. One says
CD60B
230 VAC
150 uF
60 H
It has yellow wires. The other has black wires and says
CBB60
15 uF + - 5%
450VA 60Hz
Is there a way to check them, are they both start capacitors? How do I be sure they are discharged so I don't get bit? They don't have connectors. I would have to cut wires and put back with butt connectors.
Any ideas what is wrong will be appreciated.
Leo

Bob · Jan 18, 2015

In addition to the start cap, you could have low voltage/poor connection issues with the power to the motor, a failed centrifugal switch, or an open start winding.

The BIG one (150uF) is the start cap.

Look for discoloration, leakage, or swelling, as any of those signs would make it quite likely the cap has failed.

I would check by grabbing a spare cap from my collection of them, and sub it, which is the most reliable way to verify if the cap is the problem, but I'm gonna GUESS you don't have an assortment of them lying around?

They aren't real expensive if you have a motor shop in the area, or you can even rob one from a spare motor to test.

You are looking for one with AT LEAST as great of a voltage rating, and similar uF rating. For testing purposes, one with between half and double the uF rating will start them motor IF the old cap has failed.

As far as getting a shock, motor caps tend to self-discharge pretty quickly when power is removed, and some even have a resistor to hasten that process. Or, you can usually simply short across them with an insulated tool, but it sounds like your modern motor is set up to prevent that!

Give the caps a few minutes to discharge and wear gloves, you'll be FINE!

ldj · Jan 18, 2015

Bob,
Thanks very much. You win the bet, I don't have any capacitors laying around. You have given me what I need to know. I'll buy a capacitor and try it. However the old one looks good.

Bob · Jan 18, 2015

You CAN try checking it with an Ohmmeter, but the results will not necessarily prove that it function under load and start the motor.

That's why I suggested subbing it.
ONE way to try hurt yourself...

old · Jan 19, 2015

I had the same thing happen to my compressor this year. Motor is a G.E. if I remember right and found they have a start switch that can not be replaced or fixed. Had both caps checked at the local motor repair place and both checked good . Still have not replaced the motor since I have yet t to find one in my price range

jeffcat · Jan 19, 2015

Yup.. some motors only have a start cap and some motors have a run cap also. See this all of the time at work cause the motors run almost non stop. If they shut down sometimes they will not restart. Unplug the motor and short the two posts with a screw driver. If any charge is left you will hear a little SNAP. Most of the 120volt small motors have a 7.5mf cap for start.

Ted in NE-OH · Jan 19, 2015

The first thing I would do is blow out the motor
with compressed air.Their may be dirt in the
centrifugal starter switch. That does not cost
anything.

showcrop · Jan 19, 2015

on the machines that I used to work on it was the start switch 95% of the time.

buickanddeere · Jan 20, 2015

Replacement generic external starter switch.
http://www.reliance.com/mtr/stearns/cat902.pdf

ldj · Jan 20, 2015

I carefully cut the wires and took the capacitor out to take into town to have it checked. But I forgot to take it when I went to town. However when I got it out I touched the 2 wires together and got a bright spark and a loud crack. When I got back about 6 hour later I touched the wires again and got a small spark. Would this mean the capacitor is good or does it mean nothing.

buickanddeere · Jan 20, 2015

Sounds like that was a power factor correction "run" capacitor that is in good working order.
As previously stated the starter switch and start capacitors are suspect. 5 minutes with a ohm meter would find the problem(s).

ldj · Jan 20, 2015

(quoted from post at 21:56:36 01/20/15)
Sounds like that was a power factor correction "run" capacitor that is in good working order.
As previously stated the starter switch and start capacitors are suspect. 5 minutes with a ohm meter would find the problem(s).

B&D. I'll check that out tomorrow. The cap that I cut loose and had the spark from is the one Bob said was the start cap. If I understand you, you say it is the run cap. Now, should I cut the other on loose and check it?

ldj · Jan 21, 2015

I checked the caps as in the link Bob posted. The cap with 230 v and 150 uF checks good. The cap with the 450 v and 15 uF checks bad. Another note is that cap didn't produce a spark when I was discharging it.

buickanddeere · Jan 21, 2015

(reply to post at 12:30:35 01/21/15)

Usually the run capacitor is an oil filled metal can and has a lower uf than the start capacitors. It's almost always connected to only the main windings.
A start capacitor is usually a cheaper electrolytic capacitor . Usually in a ceramic case and a paper looking cover under the terminals.
It's not unusual to find a start capacitor with the terminals burned off or the cap blown to bits.

ldj · Jan 21, 2015

Both of these are blue plastic and have what appears to be be cardboard under the connections, the 450v 15uF is about 1" shorter. It's the one that checks bad. If that is the run cap would that keep it from starting? The start switch looks good.

JMOR · Jan 21, 2015

(quoted from post at 15:38:42 01/21/15)
Both of these are blue plastic and have what appears to be be cardboard under the connections, the 450v 15uF is about 1" shorter. It's the one that checks bad. If that is the run cap would that keep it from starting? The start switch looks good.

hat link Bob posted showed more than one checking method. What did you use, applying voltage or ohmmeter?

ldj · Jan 21, 2015

(quoted from post at 16:20:18 01/21/15)

(quoted from post at 15:38:42 01/21/15)
Both of these are blue plastic and have what appears to be be cardboard under the connections, the 450v 15uF is about 1" shorter. It's the one that checks bad. If that is the run cap would that keep it from starting? The start switch looks good.

Click to expand...

hat link Bob posted showed more than one checking method. What did you use, applying voltage or ohmmeter?

Analog volt/ohmmeter

JMOR · Jan 21, 2015

(quoted from post at 17:47:44 01/21/15)

(quoted from post at 16:20:18 01/21/15)

(quoted from post at 15:38:42 01/21/15)
Both of these are blue plastic and have what appears to be be cardboard under the connections, the 450v 15uF is about 1" shorter. It's the one that checks bad. If that is the run cap would that keep it from starting? The start switch looks good.

Click to expand...

hat link Bob posted showed more than one checking method. What did you use, applying voltage or ohmmeter?

Click to expand...

Analog volt/ohmmeter

ine. Sounding more & more like the start switch. With a centrifugal start switch arrangement, it should start even with an open run cap.,

ldj · Jan 21, 2015

OK, The way I checked the start switch was visually looked in there and all springs are in place and I stuck screwdriver in there and the switch does move up against the springs and returns. I suppose there could more wrong with it than being tore up or stuck and not moving. I'll take motor apart so I can get to it. What should I look for?

JMOR · Jan 21, 2015

Make sure there is electrical continuity thru the electrical contacts of the switch.

ldj · Jan 21, 2015

I got switch out and it is good. At least I found which cap is start. A wire from switch goes to the 230v 150uF cap and I get continuity from switch to that wire. Of course I can't be sure the little arm on the switch that closed when it touches the centrifugal mechanism is closing and won't be able to tell until I put together. I'm thinking about bending it a little to make sure.

I won't be able to fool with it for a couple days. Thanks for info. so far.
L.D.

buickanddeere · Jan 22, 2015

(quoted from post at 15:38:42 01/21/15)
Both of these are blue plastic and have what appears to be be cardboard under the connections, the 450v 15uF is about 1" shorter. It's the one that checks bad. If that is the run cap would that keep it from starting? The start switch looks good.

It's a start cap with the cardboard that has failed.
I'm not 100% certain what you have there is a total of two caps, a run and a start? Or three caps with a run and two starts?
Replace all start caps with equal or higher voltage ratings and uF ratings. The higher the voltage rating the lower the chance the cap will blowup from a voltage spike. The higher the uF number the more starting torque the motor will have.
I'm fairly certain the 450V and 15uF is the run cap that is always powered up when the motor is running.
The run cap is the tin can with oil inside. The uF number will be lower than the start cap(s).
You need an ohm meter to check continuity of the start switch. By guess and by golly eyeballing an electrical circuit misses a lot of faults.

Need help with motor on compressor

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