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Air Compressor Issues (Solved)

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HodgePodgeGarage

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I’ve been lurking on this forum a long time for research and info, but just joined today because I have an issue and just can’t figure it out!

I bought a used 80 gallon, 5 HP, 220v, single stage compressor from an auction a while back. It was advertised as fully working and when I got it wired up at home, the motor immediately started smoking, would trip the thermal breaker within seconds, and, well, the motor was toast. Long story short I got my money back and got to keep the dead compressor.

I replaced the motor with a 5 HP Vevor motor with the same specs. Once that arrived, I hooked it up, and it would fill the tank to 80 PSI and then trip the thermal breaker on the new motor (no smoke). Deeper inspection into the compressor showed that the pump was quite worn out and it was blowing oil into the tank. Rather than rebuild the pump, I figured I’d just replace it with a McGraw two stage pump rated for a 5 HP 220V motor from Harbor Freight because I didn’t have much invested into the compressor and being that they’re rather simple machines, I figured that not much else could be wrong with it.

It took me a while to get everything together because I had to order a new belt, mount the pump head, modify the motor mount, and get a new compressor to tank hose. Got the belt first, changed the oil, ran it with no load to break everything in.

Now I have everything hooked up properly and it is tripping the thermal breaker on my motor once the tank gets up to around 40 psi. (not my circuit breaker at the electrical panel). I’m stumped! What else could be wrong? Could the pressure switch be bad? It’s the only thing besides the tank that’s not new now. Could my new motor be bad? The pressure switch is a Condor MDR 21-EA-11. I’m at a loss here and would love to get this thing up and running! There is significant pressure in the tank, so the only other thing I can think of is the gauge isn’t reading the pressure properly and it is reaching the cut off pressure set on the pressure switch, but I have tried adjusting the switch with no improvement. The pulley is sized per spec for the pump head.

Thank you!
 
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The Cobbler

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what size wire is running to the compressor,
is it wired to 240 volts & you're running it on 120 volts?
how many RPM's is the compressor spinning at ?
it won't be the pressure switch unless the gauge is wrong and the pressure switch isn;t cutting out, but even then, the pressure release should pop off if it's overpressuring.
 
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HodgePodgeGarage

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It is wired up to 220V with 10 gauge wiring and a 30 amp double pole breaker. The motor is a 3450 RPM motor. I’m not sure of the actual compressor pump RPM, but it is stated in the manual that it should be 1180 RPM with a 5.6” pulley (which I have).

The only other thing I can imagine it being is there’s a bit too much deflection in the belt, but I’m gonna need a small bottle jack or belt jack to get it any tighter. Doesn’t appear to be slipping.
 
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HodgePodgeGarage

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The Cobbler said:
a loose belt is not causing your issue.
what is the pulley size on the motor, and what size on the compressor ?
have you confirmed you have 240 volts at the motor?
Click to expand...
Pulley on the motor is 5.6”. Not sure of the compressor til I get home and can measure.

Have not confirmed 220 at the motor, but I have no reason to believe there isn’t 220 at the motor. I can verify with a multimeter tonight.
 
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mm08822

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Is it running in the correct rotation? Check directional arrows. The blades on the compressor pulley should blow air over the pump.
 
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whateg01

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May Pop said:
Perhaps it should have a 1725 rpm motor. So it’s spinning the pump to fast. Just a thought
Click to expand...
It has an 18" pulley so a 6" pulley on a 2 pole motor puts it right at that 1180 specified. The appears to be only 1 McGraw 5 HP compressor pump on the site.



Op,

Can you provide a link to the motor? When you say the same specs, which specs are you referring to? (Not saying you did, but some people might just look at the mounting holes for example.)

You seem unsure where the pressure gauge is right. Check it and see.
 
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mm08822

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I looked at the Vevor 5HP motors. Do you have a true 5hp motor or a 5HP-SPL.........A Vevor true 5 hp draws 25A while the SPL is only at 15A.

Pic of motor nameplate or link to motor is needed.
 
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PoorUB

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Yes! What is the amp draw on the motor?
A which pump did you buy from HF, item number? Never mind, I see it in another post.

I suspect ypu have one of those 5HP special motors that is really about 3HP, and trying to spin a honest 5HP pump.

At this point I would guess you need to change the motor pulley to one about half the size and slow the pump down so the motor can handle it, but interested on the motor specs!
 
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mm08822

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whateg01 said:
It has an 18" pulley so a 6" pulley on a 2 pole motor puts it right at that 1180 specified. The appears to be only 1 McGraw 5 HP compressor pump on the site.



Op,

Can you provide a link to the motor? When you say the same specs, which specs are you referring to? (Not saying you did, but some people might just look at the mounting holes for example.)

You seem unsure where the pressure gauge is right. Check it and see.
Click to expand...
I also found the manual on HF and agree OP does have the correct motor pulley
 
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mm08822

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PoorUB said:
Yes! What is the amp draw on the motor?
A which pump did you buy from HF, item number? Never mind, I see it in another post.

I suspect ypu have one of those 5HP special motors that is really about 3HP, and trying to spin a honest 5HP pump.

At this point I would guess you need to change the motor pulley to one about half the size and slow the pump down so the motor can handle it, but interested on the motor specs!
Click to expand...
And probably a shorter belt too.
 
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HodgePodgeGarage

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Ok. I’m back home and going to head out with my multimeter. Discovered mine was toast, so I had to run out and grab another.

My Vevor pump is the 5 HP SPL. This is the exact spec of the original Century AO Smith motor that was in my compressor when I got it. Yes, the pump was upgraded amidst all this (but recall the thermal breaker tripped on the new motor with the old pump head before I changed the pump out). It is possible I’ll need to change the motor out yet again. I’m not opposed to that if it is determined that it’s the issue. Just don’t want to throw money where it’s not needed.

This is the motor:

This is the pump head:

As mentioned above, the motor is 3450 RPM, which is properly spec’ed to the McGraw pump head’s needs (to put it at 1180 RPM with a 5.6” pulley).
 
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whateg01

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As mentioned above, you do not have a 5 HP motor. That's barely a 3 HP motor. I didn't look at the specs for the pump, but you might be able to slow it down with a smaller motor pulley to use it, but it's not really the right combination, no matter what you took off of the compressor.
 
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The Cobbler

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based on known pulley size , rpms etc, your compressor pulley is in the area of 16"?
a 5hp spl motor probably does not have enough power to spin it that fast under that load
you could try reducing the pump rpm to about 750 rpm by putting a 3.5" pulley on the motor and see if that does anything.
I am also still interested in voltage at the motor, is this an existing or new circuit that was run? there's been several threads where people think they have 240 but only have 120.
edit, previous poster posted as I was typing.
 
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HodgePodgeGarage

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I have just verified that there is 240V at the pressure switch on both sides of the switch, as well as at the connection to the motor.

So, I guess I need to be looking at the bigger motor, eh? I have no problem getting a different motor. I upgraded the pump head in the middle of this project, so if that is the likely culprit, then I’m willing to change it out.

The motor I have now is the same as the original motor, but due to issues with the original pump, I upgraded that mid project.

This appears to be a true 5 HP, 22 Amps, and a 7/8” shaft (I’ll get a new pulley). I did not realize that until you all mentioned that above, so thank you (this is my first big compressor).

Is there anything else I should check before attempting to get the bigger motor?

Thanks!
 
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HodgePodgeGarage

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The Cobbler said:
based on known pulley size , rpms etc, your compressor pulley is in the area of 16"?
a 5hp spl motor probably does not have enough power to spin it that fast under that load
you could try reducing the pump rpm to about 750 rpm by putting a 3/5" pulley on the motor and see if that does anything.
I am also still interested in voltage at the motor, is this an existing or new circuit that was run? there's been several threads where people think they have 240 but only have 120.
edit, previous poster posted as I was typing.
Click to expand...
Just measured and the compressor pulley is 16.5” edge to edge, so I would imagine the surface the belt rides in is 16”. It has a pretty large lip.

It seems from others in this thread, and yourself, that the motor is not correct for this pump, so I’d rather swap out the motor for the proper one. I just checked and I’m still in the return window for the motor too, so that makes it even easier to make the switch to the proper motor.
 
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HodgePodgeGarage

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hans109h said:
The fact that both motors overheated on different loads points to improper wiring. Can you confirm voltage and wiring to both hots, not neutral?
Click to expand...

That’s what I would think also, but I have verified the voltage is correct. I can double check.

I wired the outlet myself, and verified by my uncle, who is a commercial electrician before I closed it all up. I’m confident in my wiring but it’s always possible a mistake was made.
 
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HodgePodgeGarage

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Just for kicks, I connected my pressure gauge from my engine cylinder compression testing kit to the tank outlet and the pressure matches the gauge on the pressure switch.

So I think it’s narrowed down to either a bad pressure switch or incorrect motor. Idk if a bad pressure switch could create these issues though, or if it’s even possible it’s bad?
 
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HodgePodgeGarage

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hans109h said:
I am leaning to agree that you'll need to upgrade the motor then. You did put oil in the pumps?
Click to expand...
Yes. Put oil in the pump, ran for 45 minutes with no load per instructions I found online (no issues with the motor with no load), and then changed the oil. Detergent free SAE 30 compressor oil.
 
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whateg01

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HodgePodgeGarage said:
....

So I think it’s narrowed down to either a bad pressure switch or incorrect motor. Idk if a bad pressure switch could create these issues though, or if it’s even possible it’s bad?
Click to expand...
Your pressure switch is not causing the motor to trip its overload. The motor is overheating because it's working too hard to try to turn the pump that fast.
 
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HodgePodgeGarage

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🤦‍♂️🤦‍♂️🤦‍♂️

Out of curiosity, I just pulled the compressor back out from the wall and looked at the motor late with the info. They sent me a 2 HP SPL and not the 5 HP SPL I ordered!!! They look exactly the same and have the same frame, so I didn’t even notice.

Processed a return and it’s going back tomorrow.

Going to order the true 5 HP and a 7/8” pulley to replace since I upgraded the pump in the process of all of this.

Thanks for all of your help. I’ll report back when it’s all said and done!
 
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