More Air Compressor Repair Help

[HomeTheaterMan]

Well, I'm officially stumped. I previously posted about my Kobalt 80 gallon compressor dying on me. It seems like a relatively simple device. I tested the switch and it is working properly. Power is coming through it as it should. I even bypassed the switch in my initial testing with the original motor. It's getting power to the motor, but the motor doesn't even attempt to spin. I can spin the pulley for the pump easily by hand, so the pump isn't locked up. The capacitors also tested good with my meter. So I assumed it had to be something inside the motor.

Well, I bought a new WEG motor which came with new capacitors and I got it installed tonight. I can't get this one to run either. It's like it's just completely dead, just like the old one. I've tried the thermal reset on both and that's not the issue. I wired it like it says on the sticker on the side and I've included pictures so that you all can double check to make sure I'm wiring it as it says. I hooked the blue and black wire to the hot black line. I hooked the yellow wire to the hot white leg. I hooked the brown wire to the red which is what the diagram seems to indicate. Then I hooked the green ground wire to the green screw at the bottom of the wire box (if that's what you call it) on the motor. Both the white and black hot wires are showing 122.8 volts on my meter where they connect to the corresponding wires on the motor. I just can't figure out why it won't even attempt to spin.

Any advice on where to go from here? I'm completely lost.

 

[Bert_]

The motor does not care if you have 120 volts. The motor needs 240 volts between line 1 and line 2.

You need to test between the two hot wires. Testing voltage to ground does not tell you anything useful.

 

[micromind]

The motor does not care if you have 120 volts. The motor needs 240 volts between line 1 and line 2.

You need to test between the two hot wires. Testing voltage to ground does not tell you anything useful.

I agree.

I suspect that there is 120 to ground on black and on white but 0 from black to white.

If so, look at the breaker feeding it. measure voltage between the two output screws on the breaker with it turned on. If it's 240 then the problem is from the breaker to the motor.

If it's zero then either the panel has problems or it's the wrong type of breaker.

A pic of the panel would help a lot.

 

[Bert_]

I agree.

I suspect that there is 120 to ground on black and on white but 0 from black to white.

If so, look at the breaker feeding it. measure voltage between the two output screws on the breaker with it turned on. If it's 240 then the problem is from the breaker to the motor.

If it's zero then either the panel has problems or it's the wrong type of breaker.

A pic of the panel would help a lot.

Bad breaker was my guess since he already tossed a pressure switch at it and it didn't stick.

But @HomeTheaterMan you really need to do some simple testing before guessing at a breaker.

 

[HomeTheaterMan]

So when you're saying check it across the white and black hot wires instead of to ground, are you just leaving the meter in volt mode and putting one lead to each hot wire?

 

[The Cobbler]

yes, measure voltage between both hot leads

 

[HomeTheaterMan]

Bad breaker was my guess since he already tossed a pressure switch at it and it didn't stick.

But @HomeTheaterMan you really need to do some simple testing before guessing at a breaker.

I didn't put a new switch on it, but I unhooked the switch and wired the hot wires directly to the motor wires and it didn't run.

I also have a disconnect right before the compressor. So I'll check it at the breaker. I just want to make sure I'm doing it correctly.

 

[HomeTheaterMan]

yes, measure voltage between both hot leads

Looks like I'm getting 9-10 volts coming into the hot wires at the switch when I'm doing that. So now I'm thinking it's got to be the breaker or the disconnect now. I'm going to pull the panel cover off and check at the breaker now.

 

[American Locomotive]

It's a little confusing, but for "240V" devices in the U.S., you have two "hot" legs of 120v. Without getting into the details, one leg is exactly the inverse of the other, so you can think of one being "120V" and the other being "-120V". So if you measure across both, you will get 240V, but if you measure them individually two ground/neutral, you will get 120V.

IF something is wrong with the breaker/pressure switch/wiring where you lose one leg, but the other leg is still fine, you will measure that 120v everywhere, because that 120v is still going into the motor's windings and out the other wire. It's just not flowing because there's a break.

That's why for 240v circuits, it's important to measure across both hot legs, because otherwise you won't have the full picture.

 

[The Cobbler]

check to see if the breaker is on opposing legs in the panel .

 

[Shoreline_]

If you dont have 240v leg to leg then check it at the breaker. Could have a bad breaker.

 

[HomeTheaterMan]

Thanks guys! I found the problem and I feel really dumb that I didn't identify this at the beginning. I just thought the motor was getting power since my non contact voltage tester was showing power, then the meter was if I checked each leg to ground. Turns out I wasn't getting power on both legs.

I started checking at the breaker and had 244.8v there. I moved to the disconnect box and had the correct voltage going in, but not coming out. I pulled the cover off and discovered there was a fuse on each leg and one was blown. It's been long enough since I put the disconnect box in that I forgot it was fused. I swapped this out and I'm back in business.

 

[Bert_]

Guessing you have a 30A fused disconnect.

For future reference most are not rated for 5hp. Anytime I install a breaker or fuse for a 5hp motor I would select at least 40 amp so you don't have nuisance trips like this.

 

[micromind]

The only time I install a fused disconnect kit when I actually need fused protection. Otherwise, stuff like this happens.

 

[HomeTheaterMan]

Guessing you have a 30A fused disconnect.

For future reference most are not rated for 5hp. Anytime I install a breaker or fuse for a 5hp motor I would select at least 40 amp so you don't have nuisance trips like this.

That is correct. It's a 30A fused disconnect. I've had this setup for years without an issue until now, but I'm wondering if I should go ahead and upgrade it.