I have a small compressor that I use mainly for compressed air and small air tools. Recently it started buzzing instead of kicking on when the pressure drops. It doesn't do it all the time. Now, if I don't flip the switch when it starts buzzing it will throw the breaker. I have taken the belt off and the motor runs free and works perfectly with the pressure switch. I also turned the compressor pump pulley by hand and it has resistance but is no trouble turning. But, when I replace the belt and add the required tension it will kick on and just buzz. I sometimes can throw the switch off and back on and it will take off. But as time goes on it is getting worse. My question is, as I have no clue about compressors other than what comes out of the end of the hose, what is causing this, the pressure/ off-on switch, the pump, or the motor? I just bought a new compressor for the big shop and really don't want to buy a second one as this is the one I was using in the shop and moved to the assembly area for the air. I had one that worked fine but I gave it away a while back because it was a diaphram compressor and made enough noise to hear down the street with all the doors and windows closed and driving me nuts. Just to set the stage here, this compressor in question is about 30 years old, is a 1 HP with a 20 gallon tank, and when it pumps instead of buzzing will outwork the damn thing I gave away. Sooo.........any ideas from you compressor gurus?
You could have a bad capacitor on the motor, you can change them for pretty cheap.Its worth a shot. Also make sure that there is no pressure on the head when it is restarting,there should be a vent(blowdown) line that runs to the pressure switch. make sure when it comes up to pressure and shuts down that this line is venting the head pressure off.The shrader core that makes the hissing noise could have come loose and is not contacting the armature.
Also pop the cover off the pressure switch and look at your contacts, if they're really pitted you could be getting a poor connection, or if the armature of the solenoid is cracked or weak under the contact set it will do the same thing. The fact you can flick the switch on and off and get it to run makes me think the problems electrical, and in that switch.
Like Medler1 said, it could be the unloader that takes the head pressure off of the cylinders. There is usually a little one way valve that screws into the top of the tank, where the air goes in from the compressor, with a skinny little line that runs up to the switch. The idea is that when the tank comes up to pressure and the motor shuts down, this valve bleeds pressure off of the cylinder(s) so that the next time the compressor has to start the motor isn't fighting all that compression in they cylinders. It allows the motor to start spinning easier. Our compressor started doing exactly what you describe and we were blowing fuses left and right. Found that the unloader valve was sticking because some little debris was getting in there and jamming it open, so the full tank pressure was still on the head when it was trying to restart. Ended up the debris was the head gasket from the compressor, it was coming apart and junk was going down the line. Replaced the gasket, cleaned the unloader, and no more problems. Your problem could be something else, but this is one possibility. Don
I've had a number of compressors over the years, and two in the last five did exactly what you describe. Changed capacitors, motor was free, and the head unloader worked.... Nothing worked. Turns out it was the start winding switch in the motor, it burned out and wouldn't allow the motor to start with the aid of the start capacitor (s). Bad part was both motors were outdated so I had to buy a new one...
I had the same problem with outdated start winding switch. Went to a electric motor repair shop thay turned me on to a small universal solid state motor starter that wires in external. It saved my old table saw a few years ago. Ron
Ok, here's an update, I replaced the switch with a new unloader. Damn, had to refab everything. Now, it starts fine but when it gets up to 80 PSI it stops and starts making that same buzzing noise it did previously when it wouldn't start. I removed the belt and hand turned the pump pulley and it's smooth and easy with no drag. Is it possible that the motor is getting weak and when to pressure reaches the 80 PSI mark it gives up the ghost? Oh, now I can release the pressure in the tank and as soon as I get it back down to 50 or so it will then run again until around the 80 mark. If I don't hit the switch and turn it off in a few seconds it will trip the 20amp breaker. If used to go to 125 in no time at all. I'm determined to keep this old compressor so help.......................................
Do you have a way to check the amp draw at 80 psi ? This is going to be the next step and then check the name plate on the motor and see where your at. Normally on a compressor you can run slightly higher than name plate with the service factor. to find out how high you can take the amp draw on the name plate and multiply it by the service factor and thats as high as the motor will handle at its unload point. 13a x 1.15 sf = 14.95a for example.
Have that problem on mine. There should be a one way valve just upstream of the unloader valve. If that valve sticks open, the unloader can't do it's job, and the pump is too hard to turn. There should be zero pressure at the pump outlet, before the compressor gets switched on. Then the pump is easy to start. Understando ?
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