I have a 2.5 HP 220 volt air compressor. The motor overheats and drops out on the resettable breaker/thermal limit after five minutes of run time. This problem has been getting gradually worse over five to ten years, and now the compressor shuts off before it can pressurize the tank completely.

My guess is that something is getting plugged up with debris and causing the motor to work too hard, but I'm basically just guessing. There's no real indication of anything wrong with the motor except it gets hot after a couple of minutes of run time. It starts and runs fine until it overheats.

The oil level in the compressor is fine.

Unfortunately, I don't know beans about compressors, so I don't know how to troubleshoot this problem.

 

That's what symptoms I saw developing. It was the pump that was failing. Not the motor driving it.

 

I’m unsure what is causing the problem. It is confusing when you say “problem has been getting gradually worse over five to ten years”. With a very gradual worsening of the problem over a long period of time, I’ve identified a few things you might want to check. Usually when a motor part is going bad, it fails within a shorter period of time than described. So your instincts of “something is getting plugged up” is sensible.

If you’re proficient in using a volt/amp meter, you might want to troubleshoot a possible electrical problem first. Low voltage can cause a motor to overheat thereby blowing a fuse or tripping a breaker. If you’ve added anything to that circuit over time, and its drawing amps simultaneously when operating your compressor, that might explain the problem or you could have an electrical issue unrelated to compressor. Readings should be taken on the line side without the compressor operating to assure your power supply is okay. If that checks out, take readings with compressor motor running (especially an amp reading just before it shuts down) as that will give you additional information before deciding any next steps. For example, if you find that amps are within limits set forth on nameplate, that might suggest a bad breaker since you probably have difficulty remembering how "hot" the motor got after running five minutes in past years. Be very careful if not familiar with electricity since 220 volts can be lethal or start a fire should both 110v hot legs go to ground.

From what you described, it doesn’t seem like a pressure regulator problem whereby the motor doesn’t cut-off (i.e., no mention of air pressure exceeding its cut-off point).

Some other things you might want to check: (i) air filter (if equipped) to assure it’s not clogged, and (ii) tank drain (may have an automatic drain or needs to be manually opened) to assure it’s not holding a large amount of water.

 

This is a belt driven oil based piston compressor.

I installed a separate 220 volt circuit for this compressor about 10 feet from the breaker box a few years ago. The problem existed before and after I added this plug in wiring outlet.

I'll have to check some of the things suggested. Thanks for the ideas.

And Rob, you are correct that the pressure doesn't exceed rated limits. It will shut off if it gets to the rated shut off pressure. Sometimes it will get to that rated pressure before the motor limit pops if the motor starts cold, but it will usually pop the second time after the motor starts when it's already warm.

 

I operated the drain valve while the compressor was operating ---- no water or moisture.


The air filters on this unit are minimal --- and at that one was missing.

The other more or less fell apart when I removed it.

That exposed the valves underneath the air filters, two sets of two valves each --- I'm supposing that indicates two cylinders.

The valve set that had had no filter was each opening. The other valve set was not opening, although they would open if I pushed on them with a screwdriver.

I'm guessing that might be the problem. The valves weren't firmly fixed in place like I would suppose they would be if they were controlled by a push rod. I could easily open them by pushing on them with a screwdriver.

Does that offer some meat for some further advice and ideas?

 

Your troubleshooting seems to rule out a power supply problem. Like you, my thoughts then turned to finding a restriction issue.

While difficult to judge what is normal vs. abnormal for running hot to the touch, it seems that your motor is excessively overheating causing the thermal switch to trip out as it is designed to do. Your last post about what you found with respect to the air filters makes me wonder if the problem might be a leaking head gasket seal rather than an air restriction issue. This might explain why your problem is gradually worsening over time as the seal deteriorates. This is also consistent with a motor overheating after running for 5 or so minutes. Another clue might be whether you know if it is taking much longer to pressurize the tank as it once did say a few years ago.

One other thing not specifically said. I’m assuming you’re not seeing any loss of pressure after the motor shuts off and no air is being dispensed. If not, I think this points us back to the motor.

Here are two links you might want to read to see if they provide any clue(s) in helping troubleshoot the problem: Compressor blowing head gasket on one head; Head gasket keeps blowing. A third link allows you to direct a specific question about your problem: Miscellaneous troubleshooting compressors; simple diagnosis and remedies to get.

That exhausts my ideas for trying to isolate the cause. I’m not an expert on air compressors as my limited knowledge comes from troubleshooting problems I’ve encountered with mine, and those involved non-motor related issues. I wish I could have been of more help. Good luck!

 

Thanks for your comments, Rob.

Now that your mention it, the air filter was contaminated with oil when I removed it. Not dripping, but there was definitely oil there after operating the compressor for only a couple of minutes. The other set of valves was dry.

I seem to remember that oil where it shouldn't be is a common symptom of a blown head gasket on cars, and perhaps that would explain why the valves weren't operating on that cylinder either. I'm guessing that indicates no compression and hence no suction to open the valves.

Hmmm.... a further thought: The air filter material was held in place by a bolt that went through the head and into the main body of the cylinder. I had to loosen up that bolt to pull out and inspect the air filter material, and I switched on the compressor after doing that to observe the valve action without tightening up the bolt again. I suppose that could have caused the head gasket to fail even if it hadn't failed before.

The air filter on the dead cylinder was contaminated with oil even before I switched on the compressor with the bolt loose, though.

 

I pulled the head off the compressor today. Frankly, I couldn't really tell if the head gasket had failed or not.

I ordered a new gasket from Sears, which was available despite the compressor being 25 years old.

I'll give it a shot and see if that solves the problem. My diagnostic skills on this kind of problem are small. One of the two cylinders wasn't causing the valves to open, which I suppose indicates no compression, and the same valves had some oil on them.

The valves for the other cylinder were visibly operating and were dry.

Is it likely that a blown head gasket will cause the motor to overheat?

 

Finding oil on valves on a compressor is never a good thing, in my opinion. Hopefully you just need to replace a valve plate.

(But in all honesty, I'm guessing rings. Where else would the oil be coming from?)

 

When I took the head off the valves looked perfectly fine to my inexperienced eyes.

The cylinder had no accumulated oil.

I seem to remember that a blown head gasket causes coolent to mix with oil in a car engine, so I was guessing a bad head gasket might cause no compression in that cylinder, causing the valves not to operate and cause oil to get in around the valves.

But from your comment it sounds like that probably isn't what's going on.

My diagnostic skills here range from minimal to pathetic.

 

A bad valve could easily cause the blow-thru. I don't know. I'm hoping you're right. Oil buildup is (in my opinion) not a good sign.

 

I had the same sort problem with my compressor. I ended giving to my buddy to fix, been a couple months now and my buddy still has it. I hope you get yours fixed soon, good luck!

 

typical small amounts of oil vapor may get to valves in compressors, they are actually run dry to get the rings to seat otherwise they may 'push oil' for a long period of time after being rebuilt/honed, ring end gap and cylinder/piston measurement also have an effect on the amount of oil getting by. liquid test your valves to make sure they are sealing, in a simple explanation it is opposing check valves in series..one lets it in the other lets it out and they are flow sensitive.