The air compressor bogs down.
By that, I mean that that the air compressor starts normally, it begins to build pressure in the tank, but at a certain point, the compressor motor begins to slow down. The compressor motor begins to labor, the compressor motor slows, the sound changes, and the buildup of air pressure in the tank either stops completely, or slows substantially.
Sometimes, when an air compressor bogs down, that process causes a problem with the power. The motor may pull too many amps, and the circuit breaker lets go. Or, the on-compressor thermal cut out will shut down the compressor due to motor overheating.
Older pancake style air compressor
What do you do when an air compressor bogs down?
Diagnosis of the problem may not be that easy.
Many things might be the cause. A list of the most common reasons why an air compressor bogs down follows:
- Use of a too small extension cord to power the compressor. If an extension cord is being used, remove it, and plug the air compressor power cord directly into the wall socket to see if that helps.
- Use of a power bar to power the compressor. Same advice. Remove the power bar from the power supply and see if that helps.
- Too many other power-drawing appliances on the same circuit as the feed to the compressor. Ideally, an air compressor should be powered from a socket that leads directly back to a 15 amp (minimum) or a 20 amp breaker or fuse at the panel. If other appliances are in the line that feeds the compressor, shut them all down, and test the compressor again.
- The compressor unloader valve has failed. To test this, open the tank drain and let all of the air out of the tank. This will emulate the unloader valve function, and at the same time, remove water buildup in the tank. Close the drain and power up the compressor to test. If the compressor starts easily and runs up to cut out pressure, it’s time to service or replace the unloader valve.
More comprehensive checks when an air compressor bogs down on start up.
The previous checks are simple. There is one more that you should do before getting to the more complex checks noted below.
If the compressor is belt driven, remove the belt (power cord out please) and turn the pump sheave by hand. If it turns relatively easily with no binding, that helps eliminate the pump as the cause.
Most frequent cause of an air compressor bogging down!
The reality is that the most frequent cause of an air compressor bogging down on start up is a failing start capacitor. It’s now time to test this component. See the page on this site about how to do that.
If the start capacitor checks out, and your compressor has a run capacitor, check that one next. If either is not up to snuff, they must be replaced.
Now it’s decision time. Do you take your compressor motor to an electric motor shop for a load check, or do you tear down the pump to see what’s what? Your rotating of the pump sheave may help. If there was any hint that the pump may be malfunctioning mechanically, tear down the pump to check the piston rings, intake and pressure valves, and general condition of the pump innards.
If you feel that the compressor pump is OK, and the power supply to the motor and the motor caps are good, it may be time to pay for a motor load test.
If you opt for tearing down the compressor pump, depending on the age of the compressor and level of use (ie; did you forget to put oil in a lubed compressor?) you may want to replace the piston ring, valve plate and ALL gaskets to ensure that when you reassemble the pump, none of these items can be an issue for some time.
Make sure when you install the valve plate that it right side up, else your compressor pump will not work.
One last thing. Know the duty cycle of your air compressor and make sure you run the compressor within this time frame. Over use of the compressor can, too, be a factor in why an air compressor bogs down.
Bill, I have a speedaire 120V 2HP compressor. (1NNF4) Anyway it bogs down pretty quickly. When I got it it would not start at all so I replaced the starter capacitor. It would then start, but bog down so I thought maybe the run capacitor and I replace that too. It runs a little longer but then bogs at maybe 10 lbs or less and never really builds much pressure. It will stop turning. The pumps rotates freely and will move by hand even when bogging down. The motor runs great without a belt. I pulled the check valve and… Read more »
Have an old (1995) Campbell Hausfeld 2 stage compressor. Motor runs great, had it rewound couple years ago. With the belt removed the compressor turns by hand well. Trouble is it builds to about 80psi and then slows and screams, belt slips, motor continues to run but belt slips and I unplug.
Any advise?
I recently acquired a new to me vintage Kellogg American B321 compressor. I replaced the belt, the wiring to the motor, and put on a new pressure switch. Plugged her in and she started first try! Amazing. I have not gone into the guts of the compressor yet, change the oil, etc. because I wanted to see what I was working with first. She runs great until around 45 psi — then it bogs down. At around 50 psi I turned it off as it was sounding rough. I drained the air, did the same test and realized it was… Read more »
Hi, looking for some help and advice on my compair holman lt10 cummins compressor. it is running on full load for approx 10 ins and then cuts out completely.If anyone can help i would be grateful.
Mid 90’s Chicago pneumatic diesel 185 cfm rotary screw compressor bogging down after ~20 secs of run time. You can start it again immediately and it bogs down quicker. It doesn’t have any fluid level or heat sensors other than the gauges for safety cut off. Oil separator element isn’t clogged. Would this be an unloading valve issue?
I have a craftsman 191.158210 when I start it it runs fine and then bogs down about a minute. I let the air out that has built up and run it again, it still bogs down. What can I do
Craftsman 2 HP 230V 106.154780 compressor. Starts and runs but bogs down as soon as some pressure builds, then motor reset button sparks on and off. I disconnected everything but motor and compressor. Runs fine with no load, just blowing air from tank and small compressor head fitting. If I put my fingers over outlet from tank and small fitting in the head, pressure will build for 15 seconds then bogs down, I see a spark at the reset button, tries to speed up again, but immediately bogs down. It will just keep doing this but won’t build more pressure.… Read more »
I have a speedway 60 gallon 3 hp oil filled. When it get to around 100 psi it starts making noise like it’s freezing up. It’s hardwired 20 amp 10 gauge wire. The pump turns easy by hand and you can hear it compress air. I don’t know if it’s the motor or the pump
My 60 gal compressor starts fine, may run a little slow, but as it reaches 70 or 80 psi it labors real bad, and squeals very loud as it acts like its seizing up, after approximately 30 seconds or so it manages to push through it and continues to fill. As I use it the pressure drops normally and when the pump kicks back on the same thing happens. Surely these exact symptoms are a true indicator of what is wrong, can you diagnose this acurately based on my info ?