diagnose my air compressor

[Haywire]

My compressor got rained on. What it's doing is this. If the tank is empty and you turn it on, it pumps up to 150psi like normal. If it's got 75 in it, it acts like the motor doesn't have enough power to get the pump going. It turns over a couple times and hums like it's locked up.

What do ya think?
Ian

 

[vwnotrunning]

Your unloader is not functioning. Typically there are two types. One is just a check valve at the tank inlet with a bleeder orfice hole. Some use a valve / solenoid activated by the pressure switch. Both options allow the air to bleed off between the compressor and the tank. Then the compressor starts with no pressure to minimize the startup load.

 

[RobertBrown]

Your unloader is not functioning. Typically there are two types. One is just a check valve at the tank inlet with a bleeder orfice hole. Some use a valve / solenoid activated by the pressure switch. Both options allow the air to bleed off between the compressor and the tank. Then the compressor starts with no pressure to minimize the startup load.

x2
When the pressure switch cuts the motor off, you sould hear a Ssssssss as the air trapped between the motor and the check valve is released. I don't know why rain would cause this to fail but I agree vnotrunning. It sounds like the unloader is not working. Typically, it's a shrader valve on the switch, sort of like the valve on your car tire.

 

[dex3361]

The unloader valve relieves the pressure off of the head of the air compressor so it will be easier to get rolling. Graingers has them fairly cheap.
Unloader Valves Yours is likely one the ones listed as a load genie.

 

[5030]

.......... and easy to replace and cheap, compared to the motor which you'll burn the start windings out of doing what you are doing......

 

[bindian]

Tap on it lightly with a hammer or a block of wood. Spray some lubricant on it and try it again.
hugs, Brandi

 

[Haywire]

Thanks... I'll check it out this weekend.

Ian

 

[jinman]

A few more random things. . .

You aren't running it off an extension cord are you? Many extension cords are 16 gage wire. None of my compressors will run off of a long extension cord unless I use the one with 12 gage wire. Even then, the compressors are hard starting. If I were you, I'd try another power outlet also. If your outlet is not making good contact, you could be loading down the connection and maybe even causing heat build-up in your wall socket or wiring. There's a remote chance that you need a fresh/new starting capacitor too. Those are usually a snap to change on an air compressor.

 

[Bird]

I thought the first four replies sounded right . . . . . except I couldn't figure out how getting rained on could cause that; maybe just a coincidence that it happened after a rain.

But now I think Jim (jinman) has a couple of very likely culprits.

 

[mbrule]

yep, what everybody else said.

Then, don't leave it out in the rain.... LOL

 

[Haywire]

Well, the unloader doesn't seem to be the problem. I can turn it off when it's pumping up from zero and hear it release. I was running it off an extension cord, but that's never been a problem before. Today I was trying it on a 12ga cord with the same results. The electric switch that turns it on has air coming to it from the tank. I bypassed that though with no change.

I'm thinking this leaves the motor or the starting cap on the motor.

Ian

 

[bindian]

Well, the unloader doesn't seem to be the problem. I can turn it off when it's pumping up from zero and hear it release. I was running it off an extension cord, but that's never been a problem before. Today I was trying it on a 12ga cord with the same results. The electric switch that turns it on has air coming to it from the tank. I bypassed that though with no change.

I'm thinking this leaves the motor or the starting cap on the motor.

Ian

Ian,
With the unit at room temperature, turn the compressor on and fill the tank. Turn it off and bleed the air pressure to zero in the tank. Turn the compressor on. If it does the same rumming thing, it is the motor or capacitor. If you can (carefully) spin the belt or pulley a little to help it turn and it starts running, it is the starting capacitor.
If your motor is real hot to touch, it might be going out. If the motor is just warm and helping it start does not work, I would change whatever is cheaper. Which is probably the starting capacitor.
hugs, Brandi

 

[RobertBrown]

A few more random things. . .

You aren't running it off an extension cord are you? Many extension cords are 16 gage wire. None of my compressors will run off of a long extension cord unless I use the one with 12 gage wire. Even then, the compressors are hard starting. If I were you, I'd try another power outlet also. If your outlet is not making good contact, you could be loading down the connection and maybe even causing heat build-up in your wall socket or wiring. There's a remote chance that you need a fresh/new starting capacitor too. Those are usually a snap to change on an air compressor.

Good point
I've had this problem a few times myself. The voltage will vary where I live and sometimes a 12/2 x50' will work and sometimes not. My compressor has a circuit breaker that activates and kills the voltage when the motor bogs down. Even though it's a portable I keep it near the outet and run hose instead of cord. If its a long ways, I use my generator.

 

[Haywire]

And... drum roll please....

I go back out there again and it runs like a champ as if nothing ever happened. :confused3:

 

[Bird]

And... drum roll please....

I go back out there again and it runs like a champ as if nothing ever happened. :confused3:

I'm not sure whether that's good . . . or . . . bad.:laughing: When any of my equipment doesn't act right, and then later it does, without me finding and fixing the problem, I tend to worry about when is it going to do it again.:laughing: In your case, I'm now betting on the start capacitor, and of course that's nothing more than a wild guess on my part.

 

[Haywire]

True. It'll probably flake out on me in the middle of something a few weeks from now. LOL

Ian

 

[5030]

A little word of caution. The electrolytic capacator(s ) in a 220/1 motor (to excite the start windings) can knock you on your arse right now and possibly kill you if you have a weak heart. Be absolutely sure the capacitor(s) are completely discharged before getting your fingers on the lugs.

Some capacators will have dropping resistors across the hot terminals, some don't. Either way, be sure to short across the lugs with a screwdeiver prior to fiddling in there.

 

[jinman]

You know, it could be something simple like the pressure switch contacts. If it got wet, they could have corroded a bit. Low current starts were no problem, but high load starts would take more current than could be provided across the contact resistance. Now that it has cycled a few times, the switch contacts are probably making better. The best analogy I can come up with is dirty battery terminals. Like Bird said, it will probably act up again.

 

[SPYDERLK]

Perhaps it was the switch that energizes the starter winding. It could have been sticking OFF and failing to connect the starter winding. These switches are normally ON when the motor is stopped and then disconnect centrifugally as the motor starts.
larry

 

[kelloggguy]

Always run an air hose and not an extension cord.