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meteorman 04-03-2012 12:02 AM

Air Compressor Won't start
I have a Campbell Hausfeld electric air compressor. 7.5 hp built in 1993 that I just inherited. I have it all set up and am having trouble getting it going. I just moved it, and we had to lean it over in order to get it in and out of the truck. It's massive and heavy. I couldn't get it to start running, and fiddled with it. I ended up draining the oil from the compressor and a BUNCH drained out (like a gallon+) I am confused because it would only accept a quart when I refilled it. I'm not even sure if that is relevant to my current problem. I did get it to run and fill the 80 gallon tank up to full pressure. I then turned off the circuit, since I don't use it much. Now that I am trying to use it again- it won't start. Nothing, nada. just sits there, no noise, motor doesn't even try.

So I checked the power supply. it's getting 230 volts at the pressure switch. The switch is engaged and sending power to the circuit breaker (built into the compressor/not on the shop panel). The breaker is not tripped, I tripped it and reset it to check if it was working and it seems to be fine.
The motor turns easily and the compressor seems to turn over easily too.
I'm thinking it's either the motor or the capacitor. Any idea how to check those? the Red reset button does not seem to be tripped on the motor, and I can't push it.
This thing is overkill for me, and if I replace it, I'd get a much smaller unit, so it's not worth it to replace the motor.
Any ideas? is it fried? Should I have a service call for it? or just ditch it?

sublime2 04-03-2012 12:09 AM

Generally speaking, Oil filed compressors should never be laid on their side because oil can leak into areas of the motor where it shouldn't be.
They should always be kept upright.

meteorman 04-03-2012 12:12 AM

Would this keep the electric motor from turning on?
Is it toast or can it be salvaged?
I'm confused about where all the oil came from, was it WAY over full?

thanks for the response.

woodworkbykirk 04-03-2012 06:32 AM

could be the oil issue. the compressor's reset button may have tripped also. they typically have their own breaker on them to prevent burning out the motor

DexterII 04-03-2012 07:19 AM


Originally Posted by meteorman (Post 890781)
So I checked the power supply. it's getting 230 volts at the pressure switch. The switch is engaged and sending power to the circuit breaker (built into the compressor/not on the shop panel).

I am a little confused here. You have wires coming from a circuit breaker in your main panel to the pressure switch, and then to a "breaker" on the air compressor? I'm guessing, but believe that the thing you are calling a breaker is actually a magnetic starter, perhaps with a reset, and that the power should be going to this magnetic starter, and that a pair of control wires should run from the magnetic starter to the pressure switch. Do you have the manual for this air compressor, and are you sure that you have it connected properly? A 7-1/2 H.P. motor is pretty significant, especially considering that it sounds like you did not plan to incorporate a compressor this large into your shop; are your wires properly sized?

meteorman 04-03-2012 09:42 AM

My mistake, the 'circuit breaker' that I referred to is actually a magnetic starter. (i guess)
I have a 30 amp 230v dedicated circuit for the compressor. I have 12/3 romex supplying power to the compressor.
The compressor worked like this for 19 years. I didn't change anything about the wiring on the compressor, just ran a new supply line to it in the new shop.
Could the problem be in the magnetic starter? I don't see any visible burn marks or disconnected wires. Everything looks clean and solid.

I don't have a manual (that I can find) I have contacted Campbell Hausfeld for a copy of the manual.

??thanks for the responses.

DexterII 04-03-2012 09:50 AM

What does the motor tag say in regard to the number of amps at 230 volts? I am thinking that the full load amps, or FLA, for a 7-1/2 HP air compressor motor is closer to 40 than 30, and, regardless, it should be on something larger than 12 gauge wire; guessing here, but probably 8 gauge. Not being critical, just trying to help you get to the problem, but maybe it's a matter of 19 years on an undersized power supply having taken its toll on one or more of the components.

meteorman 04-03-2012 09:19 PM

The rating on the motor is 29 amps. I may need to upgrade the wire to #10, from what I read online, 10 is required for 30 amp service.

Would this keep the motor from running at all?
Could there be a problem with the magnetic starter? How would I check it?
Should I just take the the motor into a repair shop and have it checked?

DexterII 04-04-2012 07:12 AM

Please don't be offended, but I was just reading back through your post, something occurred to me, so I have to ask; how much pressure is in the tank right now? After you get the wiring upgraded, assuming that the tank pressure is down to the point that it should kick on, and that you are comfortable in doing so, I would check the voltage at the bottom of the magnetic starter, where the leads go to the motor. If you have power at that point, the problem is in the motor, and if no power at that point, the problem is in the source side, possibly the magntic starter or pressure switch, which we may be able to further diagnose, once you get to that point.

meteorman 04-04-2012 10:19 AM

I am not offended by any questions. I often miss the obvious, and my understanding of this stuff is limited.
The pressure in the tank is down to around 10psi, the pressure switch is engaged and sending power through it.
I will check the power after the magnetic starter. Thank you for your suggestion.

DexterII 04-04-2012 11:40 AM

By the way, just as a matter of a quick overview, on air compressors over say 1/2 to 1 HP and up, the current draw is such that if they were to provide direct switching of the line voltage, the points of the pressure switch would burn out in fairly short order. So, typically, the magnetic starter, in addition to providing thermal protection for the motor, acts as a relay. The power ovbiously comes into the top of the magnetic starter, and goes out the bottom of the starter to the motor. In between is a contactor, contolled by a magnetic coil, or electomagnet if you will, which is powered by one leg of the 220 line coming into the starter, which in turn passes through the pressure switch. So, in addition to checking the voltage at the bottom of the magnetic starter, you should hear a "click" when that contactor is energized.

meteorman 04-05-2012 01:32 PM

ok. I checked the voltage at the bottom of both legs of the magnetic starter or magnetic coils? There is power going in, but nothing coming out to the motor. So, I guess this is where the problem is.
Could this be because of the undersized wire?

DexterII 04-05-2012 01:53 PM

Don't take this as a green light to continue operating it that way, but I doubt it. Does the magnetic starter have a "reset" button? If so, press that, and try again. You said "the pressure switch is engaged and sending power through it", which I assumed to mean that you can see that the points are closed; is that correct? Did you hear the coil in the magnetic starter "click" when you turned the power on? Do you have an ohmmeter? If so, with the power off, disconnect the two wires going into the pressure switch, and check across those terminals, to make sure that you have continuity across the pressure switch.

DexterII 04-05-2012 03:10 PM

Just happened to think too that since it sounds like your problem is most likely in the starter, see if there is a make and model inside of it, and post that as well.

meteorman 04-05-2012 07:04 PM

Checked continuity at the pressure switch, it was fine.

There is No click when I put power to the compressor.
the magnetic starter is
Square D
Class 8911
Type DP504Z
Series A

FLA 40
240 7.5

don't see anything visibly wrong with the unit.
don't know how to check it, but I can see that I could remove it fairly easily. As long as I got the wires back in the right spots.

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