Can you help me fix my air compressor?

[Fastback]

OK, so I am in the middle of a huge project and my air compressor decides to take a dump on me, and I NEED this thing back ASAP!

I have a 17 (+/-) year old Campbell Housefield 80 gallon unit with a 7.5HP magnetek motor that is 220 Volt single phase.

I found it with a blown breaker today and when I kicked it back on it just hummed. I removed the covers from all of the starters and caps (5 in total) and found one of the caps mounted on the side with oil on the top, so in a frantic run into the city I found another unit with the same rating (But it is a bit taller)

IT STILL HUMS, but it does try n move some but it gets hot.

Is my motor junk or could it be one of the other starters/switches on the motors housing?

I really dont want to spend the $1000 to replace this motor, does anyone know if they are able to be rebuilt?

Here is a photo of the tag on the motor, if it helps?

 

[Rockaholic555]

Why not lookup a small engine shop or an air compressor service location and give them a call and see what idea they might have? A lot of times you can get some good advice and sometimes find a good resource for parts.

Sorry, I'm no compressor genius just my 2 cents.

 

[Warrenator]

Disconnect the belt, see if it will start without a load. If it runs fine unloaded, it might be the centrifugal switch, there are two windings in the motor, a start winding and a run winding, the centrifugal switch is a little spring loaded gizmo under the end cap with weights that spin out and deenergize the start winding once the motor is spinning. You can just clean the contacts of that with a little piece of paper or a q-tip and some contact cleaner. Otherwise, you can use a capacitor checker (might be one built into your handy multimeter) and check the caps. Also, make sure you are getting full voltage to the motor, your pressure switch is switching a lot of power and the contacts get burned, if only one of the contacts is burned then it might not start, just hum. Good Luck!!!!!

 

[hofferwood]

Disconnect the belt, see if it will start without a load. If it runs fine unloaded, it might be the centrifugal switch, there are two windings in the motor, a start winding and a run winding, the centrifugal switch is a little spring loaded gizmo under the end cap with weights that spin out and deenergize the start winding once the motor is spinning. You can just clean the contacts of that with a little piece of paper or a q-tip and some contact cleaner. Otherwise, you can use a capacitor checker (might be one built into your handy multimeter) and check the caps. Also, make sure you are getting full voltage to the motor, your pressure switch is switching a lot of power and the contacts get burned, if only one of the contacts is burned then it might not start, just hum. Good Luck!!!!!

What Warrenator said,
But give the motor a spin before applying power. The start cap basically tells it which way to turn.
Chuck

 

[Fastback]

Great advice I will try that after dinner!

 

[Fastback]

OK, I tried cleaning the points and removing the belt with no real change. It hums and turns over real slow, but when I kill power it spins down and does not lock up.

I am wondering if the two silver caps when out at the same time? I only changed the one with the oil on top of it, but when I took it out I discharged it with a screw driver and saw/heard an arc.

Also, I unhooked the one I did not change and powered it on with no difference from when it was connected.

So just now I tried to discharge either of them again with no arc at all??

Here is a pic of the caps if it helps

 

[Fastback]

Well, I went out and tried to use my Ohm meter to load up the caps, interestingly the new cap did not charge at the same rate as the other sister unit, or even the old one that I took out with oil on top.

So, I put the oil topped unit back with no real change in results, but I did bump the motor over with the switch several times and it took off, so the motor is good, it just wont start from a dead stop.

I think I am going to try n track down a matching pair of new starter caps for it tomorrow, the new one I got today states the same specs but has a different form factor, and I just dont trust it.

At least we know the motors "Run capacitors" seem to be working and the motor is good.

I will update when I have more info.

 

[OccupantRJ]

Something may be between the contact points of the internal motor starting switch. I bought a "bad" motor one time that had a thread used to lash windings together caught between the contacts. It had your symptoms. I've dealt with a few single phase motors, but I've never seen that many caps on one before.

 

[Charles (in GA)]

If the centrifugal switch which is INTERNAL in the motor is stuck, this will be the symptom. It it probably that, since you have proved the motor will come up to speed once you give it a whirl. Switch is not resetting to the low speed, contact closed position.

Charles