Problematic Harbor Freight Compressor


tomwassmer
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You say, of course it's problematic, you got it from HF! Well, I would typically say the same, however this compressor was given to me and has been working great for years. It's their 10 gallon model. I was filling the tank up today and heard the sound of it change and it now it will not fill the tank more than 50 psi. I did not change any settings on it before this happened. I'm not sure how many of you are familiar with their pumps themselves, but the oil filler cap has a little hole in it (it's maybe a 16th inch diameter). I'm not sure what it's for but I did notice that there is quite a bit of air escaping through that hole when the pump is running to try and fill the tank. If I put my finger on it and it seems as though the tank will fill over 50psi with it blocked. I took the cap apart to see if there is any clue as to what the purpose of the hole is, but I can't figure out what it's for. Any ideas (other than go buy a new compressor!)?

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probaly is your unloader valve. Google "pressure switch unloader" I have the same problem with

my compressor it wont fill above 90psi Im gonna replace my pressure switch soon. the hiss after

your compressor shuts off is the air unloading in the lines. In most cases the check valve spring

is worn out or does not seat well there's also many youtube videos that explain the fix.

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Thanks, RobJeffKing! You just helped me fix my Porter Cable pancake!

The unloader valve on my 10 year old Porter Cable pancake has similar intermittent issues. If it's open, it takes forever for the compressor to recharge. I have to manually blip it on and off to get the valve to close and the unit operating normally.

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Thanks for the responses. It's funny you mentioned that unloader valve. That valve was the reason it was given to me in the first place. It was pumping the tank up and then letting all the air out when the compressor shut off. I got that all squared away. The current problem is not happening when the compressor kicks off. It never even gets up to the pressure that trips the pressure switch to shut the compressor off. The comp. would run all day (until it blows up) if I let it, trying to reach that target pressure but it would never get over 50 psi.

Beech, I tried spraying all the different parts and connections with soapy water and found a couple minor leaks which I suspect have been there for quite some time. I think I'm trying to find a bigger leak. Actually, I just had a thought. Going back to the change in sound I heard, maybe the piston in the pump blew some sort of ring (like in an engine) and there really is no air leak in any of the other components. Maybe all the pump is capapble of now is around 50 psi. Does that sounds like a feasible explaination?

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My compressor will not pump up past 90 psi and will hold that pressure for weeks and slowly leak. Ive checked

every connection and the only one that leaks is the unloader (on the side of the pressure switch) the leak goes away after

a certain amount of air has escaped with the compressor off. The increased pressure while running is

driving the air past the weak spring or the bad seal so the compressor never obtains the cutoff pressure. I have ordered

my new switch this morning and will post back the results soon. In the mean time does your compressor hold its pressure at 50 psi? You might only find the leak at 50 psi or more. If your rings have failed in one cylinder the leak would still be contained the other piston should still pump up the tank it would just take longer. Did you

replace your pressure switch ?

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This is turning into a head-scratcher. Of course I'm not at home right now so I can't sit down and look at my unloader valve. I thought my thinking was straight as to the function of that valve, which was why I was not even considering it as a possible cause of the problem. Now I'm guessing I was wrong. I do have another compressor that works, so maybe I'll try to rig the components of that one to see if I can get the HF one working. I just can't see spending much on a low quality compressor without being sure of the problem.

Also, it's just a one cylinder compressor.

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Tommy, I'm thinking that you may have hit on the solution when you said the sound change may have been in the piston. If you have a weak o-ring that will only withstand 50 psi before it fails, then you will get the same results you described, in a one cylinder compressor.

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  • 3 weeks later...

Thanks to all who contributed to this one. I finally took it apart last night and was looking for a big problem like a cracked cylinder or something along those lines, something that I can point to and say, "AH HA, THAT'S IT!" I did find the problem, and at first it wasn't too obvious till I spotted it. There's a little reed that opens when the piston is on it's way up to push air into the tank and closes on the way back down as the cylinder pulls air in though the filter. That reed is missing a little piece in the center, therefore allowing the cylinder to pull back in SOME of the air it just expelled into the tank. That's why it can only get to a certain PSI and no higher. Problem solved..now to find a replacement reed!

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