Wierd Compressor Problem

DanG · March 15, 2009, 11:18:16 AM

I can't seem to have any normal problems. They all seem to be something wierd and off the wall. :

When my air compressor comes on it starts out just fine, then slows down to the point that it will stall the motor after a few seconds. It is a conventional, belt driven unit with a 5hp motor, not one of those noisy direct drive things. Anyway, this problem started back in the fall when the weather started to cool down. I noticed that it would do this if the temp was below about 60 degrees, but was fine if it was over that. As an experiment, I set a hair dryer on it, blowing right on the compressor case, and found that it worked just fine when I heated it up that way. All winter, I've had that hair dryer sitting there, and I have to turn it on for about 5 minutes before I can run the compressor. :

I finally dug out the owner's manual, and it says to change the oil if this happens. I got some of the recommended oil and changed it, but it hasn't helped. It has gotten worse to the point that it won't run when the temp is near 80 degrees now, unless I run the hair dryer on it first.

I'm wondering if it could be the run capacitor on the motor? It has two capacitors on it. Would the run capacitor be the smaller of the two?

LeeB · March 15, 2009, 12:35:27 PM

I'll be interested to hear from somebody that knows what they are talking about, certainly not me, but rings, piston and cylinder walls pop up to me. How many years has it got on it? How much oil does it use. I had an old comprressor that did the same thing. Used oil like crazy and finally siezed up altogether. Never did take it apart because I wanted a new one. with an approved tank. My dad had put the thing together with odds and ends years before I inherited it. I used for about 10 more after that. Went through three motors on it.

tyb525 · March 15, 2009, 12:48:51 PM

Our old compress (5hp also, 80 gal, 1930's) will sometimes stick if it hasn't run in awhile. If you don't noticed that it is stuck, the motor pulley will spin and burn right through the belt. You have to turn the flywheel/pulley on the pump by hand to get it going.

I think it is less of a problem when there is new oil in it.

DanG, I wonder if there isn't enough oil getting on the cylinder walls? Not sure how the oil is delivered, might be one of the splash-type things like some small engines use.

Also, just a thought, I wonder if some air is getting past the piston and into the crankcase, therefore creating pressure when there shouldn't be? I think there would be a valve for this, but maybe it's plugged up?

Ironwood · March 15, 2009, 12:52:41 PM

If it runs fine for a few strokes and then dies out ,could there be back pressure being created? perhaps there is a valve sticking and heating helps give it some space? Just a thought. I am no compressor guy except knowing to buy older Quincy pressure oil feed units. The Quincy's have valves most/ some others use reed valves. How about the unloader? , is it functioning when the unit fininshes a run cycle? This would be the brief "pissst" you hear right after it shuts down (having reached max psi).

The non-compressor guy, Ironwood

DanG · March 15, 2009, 01:32:59 PM

This unit is about 7 or 8 years old. I would say that it is at the upper end of the "homeowner grade" spectrum. I'm pretty sure it has reed valves and a splash oiler. All functions seem normal except what I described, including taking a healthy "pisssst" on shutdown. :D

I have noticed if I bleed the pressure way down, it does ok because the compressor is warmed up by the time the back pressure builds up.

I'm worried that I'll forget to shut it off one day, and it'll come on at night and burn its motor up.

Haytrader · March 15, 2009, 02:51:14 PM

Are you heating close to the check valve?
That is what it sounds like to me.

scsmith42 · March 15, 2009, 03:10:26 PM

I would also check the check valve; I had one that had a similar problem several years ago and a new check valved solved the issue.

DanG · March 15, 2009, 03:42:09 PM

Where would the check valve be located? I have the hair dryer pointed at the side of the crankcase.

stonebroke · March 15, 2009, 04:09:35 PM

I had a freind witha similar problem. Try using all the air that is in the tank before you turn it on. Then the motor has minimal drag until it is warmed up.

Stonebroke

Dave Shepard · March 15, 2009, 04:13:31 PM

I'm guessing there is about a 1/2" pipe going from the compressor head to the tank. The check valve should be at that connection. It keeps the compressor from having to start under load, assuming your pressure switch is bleeding off the compressor head.

isawlogs · March 15, 2009, 05:56:02 PM

It must be in need of porting :P

olyman · March 15, 2009, 06:09:36 PM

Flip the belt off,plug it in,see if the motor slows down after a while with no load.If it acts up,could be start capacitor,start windings,governor contacts burnt,etc. Take to a motor shop to see if they can fix. If it dont act up, sounds as tho something wrong inside the compressor. Pffffft means the compressor is unloading before startup. With belt off,see if compressor turns at least a little,freely. Means no bearings hung up.Which if they are hung slightly, then the longer it ran, more load on motor, and would overheat the motor, shutting it down,if the overload aint working.

Chico · March 15, 2009, 07:07:22 PM

After you ck the motor which I don't think is the prob crack the bleed on it a liitle while it runs and see if that helps it if it does put a bleeder on it and a good water trap if you don't have one I think it's definately in the valves if it were cyl friction it would get worse in warmer temps instead of better imo I'm guessing you have a carbon or gumming prob possibly one of the reed valve diaphrams but I'm thinking clean your valves up and make sure it stays dry which I know condensation is a prob down there and I think your prob will be solved

Polly · March 15, 2009, 07:50:52 PM

i got an old old two cylinder compressor ,every once in a while i will pour a little oil in the air intake , i dont know exactly what it does but it seems to help :D :D :D

scsmith42 · March 15, 2009, 09:18:35 PM

Quote from: Dave Shepard on March 15, 2009, 04:13:31 PM
I'm guessing there is about a 1/2" pipe going from the compressor head to the tank. The check valve should be at that connection. It keeps the compressor from having to start under load, assuming your pressure switch is bleeding off the compressor head.

DanG, Dave answered your question. The check valve is usually built into the brass fitting that screws into your tank, that the main feed from the compressor attaches to. Basically it's designed to relieve the head pressure on the compressor when it starts up.

isawlogs · March 15, 2009, 10:01:25 PM

DanG , open the valve on the bottom of the tank , then start the compressor , this will put a light load on the motor if the compressor still acts up I would have the motor checked .

isawlogs · March 17, 2009, 08:00:42 AM

DanG , how are you coming along with the compressor ???

DanG · March 17, 2009, 08:57:53 AM

Marcel, you apparently don't have a clear understanding of how things go around here. :D :D I might get around to looking into it further sometimes this summer.

It hasn't been forgotton, though. Yesterday I let it get down to about 20 psi before turning it on with no heat on it. It ran like gangbusters until it reached 105 psi, then slowed dramatically but didn't stall out. I felt the compressor and the cylinder was warm but the crankcase still felt cold. When I apply heat to the crankcase, it runs like it did when new. As I said before, the troubleshooting guide describes the problem and says to change the oil as a remedy. Since I had not been changing the oil like I should, I think I may have a sludge buildup. I'm thinking about draining it and putting in some ATF, running it for a few minutes, then switching back to oil. I'll be cogitating about this for an indeterminate period before taking any action, unless the DanG thing quits altogether, which is usually what it takes to get me moving. :

:D :D

isawlogs · March 17, 2009, 01:24:23 PM

If it is the motor , Knowing how resourcefull you are , ;D pull it , and get yourself a stationary bike ;D, there is a belt there from the pedals to the wheel , chuck da wheel and put the belt to your compressor .. Now you have an option , you can try and con Leendaw into kettin' on that there contraption or sit on it youself and pedal yourself some air . :P
No thankin' necessary . ;)

David Freed · March 18, 2009, 07:17:41 PM

Quote from: DanG on March 17, 2009, 08:57:53 AM
Since I had not been changing the oil like I should, I think I may have a sludge buildup. I'm thinking about draining it and putting in some ATF, running it for a few minutes, then switching back to oil.

I don't know if this will help, but since you mentioned running light weight oil for a few minutes, I thought I would tell you my compressor story.

I let the crankcase run low on oil, and the compressor locked up when a friend stopped by to use some of my air tools. I took it apart and found one of the aluminum connecting rods had seized on the crankshaft. I had to heat the rod to get it to let go. I then began spraying WD-40 on it while it was still hot to get it to turn on the crank. It turned very hard to begin with, but slowly began to get easier. When it was turning real easy, I poured 3-in1 oil on it and turned it for a while, then ATF. I then washed everything with ether, coated it with 30 weight oil, and put it back together. It runs like nothing ever happened, but I'm sure its lifespan was shortened.

RSteiner · March 23, 2009, 08:45:20 PM

I have a compressor that has quirks similar to yours but a little less horsepowered unit.

On a compressor the size you have on the pressure switch there is usually a small tab sticking out of one side of the switch housing that presses on a small unloading valve much like the one on a car tire valve stem. This is connected to the pressure side of the compressor head, its purpose is to unload the pressure in the cylinders so that compressor does not have to start against any pressure. When this valve malfunctions the motor doesn't start right or turns a few times and kicks out on thermal overload.

You could also have a bad capacitor, when in doubt change them both. The motor may run fine without a load even with a bad capacitor. As for the reason why the hairdryer routine works is a bit of a mystery especially in Florida. You may want to try to inspect the reed valves and remove them so you can turn the compressor over by hand to see if there are any tight spots.

Good luck.

Randy