Troubleshooting air compressor

[vandersmash]

I was given a 10-year-old air Craftsman Air Compressor last year that wasn't working properly. So far, I've replaced both capacitors and the pressure switch and resealed all the leaky air fittings. It will run and build pressure, but not the proper pressure. It's supposed to cut off at 150psi, but it will only make it as high as 110-120psi. That's not all, though. It also won't restart at all. If I unplug it and come back to it later and plug it in, it will run again, but it will only make it up to about 80psi and still won't restart when it discharges. I've tried to look up more info on the compressor, but the model number is conveniently scratched off (see picture). Any ideas about what I should try next?

 

[larry4406]

Welcome!

My guess is that the unloader is not working and/or you may have an issue with the check valve between the compressor outlet and the tank.

 

[vandersmash]

I'll give that a shot. Thanks.

 

[The Cobbler]

It's supposed to cut off at 150psi, but it will only make it as high as 110-120psi. That's not all, though. It also won't restart at all. If I unplug it and come back to it later and plug it in, it will run again, but it will only make it up to about 80psi and still won't restart when it discharges.

first thing is compare your pressure to a known accurate gauge .. that set point is (usually) adjustable in the pressure switch . don't rely on an unknown pressure gauge
not restarting, does it try to start or just does nothing?

 

[finn]

The check valve was leaking on my little 30 year old PC pancake compressor. It healed before I got around to buying a new one or I burned out the windings because of the high current draw when starting.

This thread reminds me that I should order a new check valve.

 

[vandersmash]

first thing is compare your pressure to a known accurate gauge .. that set point is (usually) adjustable in the pressure switch . don't rely on an unknown pressure gauge
not restarting, does it try to start or just does nothing?

It just does nothing.

 

[The Cobbler]

sounds like either a bad pressure switch or a bad connection .

 

[finn]

It just does nothing.

Take the cover off the pressure switch. The switch on my well pump fell apart once. It was pretty obvious when I looked at it with the cover off.

 

[Shoreline_]

You replaced the pressure switch did you adjust the pressure to the desired cutoff setting? Turn that ***** in so it never turns off. Run it. When you get to 140 psi back off the adjustment until the compressor stops. Turn forward a smidge. Done.

 

[Buckaroo5]

Also having trouble with a 20+ year old Craftsman 6HP 30 gal 150 psi compressor with AO Smith motor. It will start at low pressure and build pressure appropriately but will not restart when it drops below the lower pressure set point (around 110 psi). It tries to start maybe 3 times (a few revolutions) and then trips the breaker. I have checked both capacitors and they are good. I am hearing a hiss when it shuts off so I think the unloader is working. I suppose the next step is the check valve, right? Is there a way to confirm it is bad or do I just replace it and see what happens?

Sears Parts Direct says check valve no longer available, part AC-0631. Maybe this is the part I need (A19712) but Craftsman not called out. Under Black & Decker, very close to my model number (mine 919-167310 vs 919-16732 Type listed)?

https://www.jackssmallengines.com/jacks-parts-lookup/part/devilbiss/a19712?gad_source=1&gad_campaignid=16705372762&gbraid=0aaaaad_uacipmqmeykqad0nlcws3phojq&gclid=cjwkcajwuuprbhaneiwa2ji8etbyrye86gb5mxk9skrkqnhve8uewfetstvy4azhbt2yx8v4rv_cfxocox8qavd_bwe

 

[Buckaroo5]

Jack's confirmed A1972 was correct part but not in stock with no replenishment date from DeWalt. Ordered one from Ebay although likely a knock-off.

 

[Beerhippie]

Also having trouble with a 20+ year old Craftsman 6HP 30 gal 150 psi compressor with AO Smith motor. It will start at low pressure and build pressure appropriately but will not restart when it drops below the lower pressure set point (around 110 psi). It tries to start maybe 3 times (a few revolutions) and then trips the breaker. I have checked both capacitors and they are good. I am hearing a hiss when it shuts off so I think the unloader is working. I suppose the next step is the check valve, right? Is there a way to confirm it is bad or do I just replace it and see what happens?

Sears Parts Direct says check valve no longer available, part AC-0631. Maybe this is the part I need (A19712) but Craftsman not called out. Under Black & Decker, very close to my model number (mine 919-167310 vs 919-16732 Type listed)?

https://www.jackssmallengines.com/jacks-parts-lookup/part/devilbiss/a19712?gad_source=1&gad_campaignid=16705372762&gbraid=0aaaaad_uacipmqmeykqad0nlcws3phojq&gclid=cjwkcajwuuprbhaneiwa2ji8etbyrye86gb5mxk9skrkqnhve8uewfetstvy4azhbt2yx8v4rv_cfxocox8qavd_bwe

Unloader valve. Classic symptoms.

 

[Buckaroo5]

Unloader valve. Classic symptoms.

Ok - replaced the check valve and did not fix it. So I replaced the pressure switch and the unloader valve and still having the same problem.....stumbles/won't start & pops the breaker when pressure is high. Won't start unless I relieve the pressure. Ugh.......I guess I need to go back to the motor capacitor, right? I tested it and convinced myself it was good but what's left?

 

[The Cobbler]

Ok - replaced the check valve and did not fix it

I had a Craftsman compressor that wouldn't start under load. same as you the cap was fine.
I installed a cold start valve on it, here , see post 15 https://www.garagejournal.com/forum...less-wont-start-with-pressurized-tank.196633/

copy of that post

I had the same problem with a craftsman oil-less. I'm not sure of the model number, but I will get it & post it here.
It would start no problem with no tank pressure, but it would blow a breaker when the tank was full. 20 amp breaker didnt help the situation .It was brand new , but I got it at a misguided freight sale and obviously no warranty. What I ended up doing was adding a cold start unloader valve, another name is unloader assist valve available on ebay & other places.
Tie it into the pump discharge line( before the tank check valve) what it does is bleed off some of the air until the pressure reaches about 10 PSI, then the valve closes . that gives the motor lots of time to get up to full run before it has to deal with pressure on the pump. Cost was about $4 and a brass tee was $2 .



If I get ambitious I will take a few pic of my set up & post here if I can..

any questions I would be glad to answer.

 

[Buckaroo5]

I had a Craftsman compressor that wouldn't start under load. same as you the cap was fine.
I installed a cold start valve on it, here , see post 15 https://www.garagejournal.com/forum...less-wont-start-with-pressurized-tank.196633/

copy of that post

I tried the link in post #15 and it did not connect. Please explain to me why this solution would work. Is the unloader valve not sufficient?

 

[The Cobbler]

It allows the discharge air to bleed off until it hits about 5PSI . so there's several seconds that it allows the pump to spin with very little load on it . by time the cold start valve closes the motor is up to full speed & not trying to start under load of compressed air.

 

[The Cobbler]

a reasonable explanation on you tube

 

[Citation]

OP, I think you may have two problems. Let's start with not getting past 120 psi. If the motor runs fine until we get to 120 psi then the pressure switch shuts things off, that's just a pressure switch that needs to be adjusted. Many of these switches look the same but may be factory preset set to different pressure levels. Not hard to adjust the screws. However, if your problem is the pump keeps running but can't build pressure past 120, that could be a bad valve in the pump itself. A classic reed valve failure is the pressure builds slowly then can't get past some limit. If that is your issue then you need to pull the head off the pump.

The next thing is why can't you restart the pump. That sounds like an issue with the unloader valve not working correctly. Since that valve is typically part of the new pressure switch, I doubt it's broken but maybe it's connected wrong or not at all. Somehow the pressurized air in the pump to tank interconnect is not getting drained after the pump shuts off. Unloader valves are very simple so I think it's unlike to be broken. But it's possible the line is not connected correctly. Do you head a sudden psss of air just after the pump turns off? If no, then it's probably connected wrong. Note that even if the valve never opened, air will naturally leak out of the pump to tank interconnect via the valves in the pump head. However, if might take many minutes to reduce the pressure enough for the pump to restart. This is why you could restart the pump the next day but not while in use. Also, the unloader valve only affects starting the pump. Once the pump start running (just a few seconds) the unloader doesn't matter. I mean if it's open it will take longer to fill up but it will still fill up. If it's closed... well it's supposed to be closed when the pump is running.

BTW, a picture of your system showing the pumping between the pump, pressure switch and tank would be helpful.

(note: in my compressor the unloader line connects right next to the In Tank Check Valve vs at the pump head)

 

[Buckaroo5]

OP, I think you may have two problems. Let's start with not getting past 120 psi. If the motor runs fine until we get to 120 psi then the pressure switch shuts things off, that's just a pressure switch that needs to be adjusted. Many of these switches look the same but may be factory preset set to different pressure levels. Not hard to adjust the screws. However, if your problem is the pump keeps running but can't build pressure past 120, that could be a bad valve in the pump itself. A classic reed valve failure is the pressure builds slowly then can't get past some limit. If that is your issue then you need to pull the head off the pump.

The next thing is why can't you restart the pump. That sounds like an issue with the unloader valve not working correctly. Since that valve is typically part of the new pressure switch, I doubt it's broken but maybe it's connected wrong or not at all. Somehow the pressurized air in the pump to tank interconnect is not getting drained after the pump shuts off. Unloader valves are very simple so I think it's unlike to be broken. But it's possible the line is not connected correctly. Do you head a sudden psss of air just after the pump turns off? If no, then it's probably connected wrong. Note that even if the valve never opened, air will naturally leak out of the pump to tank interconnect via the valves in the pump head. However, if might take many minutes to reduce the pressure enough for the pump to restart. This is why you could restart the pump the next day but not while in use. Also, the unloader valve only affects starting the pump. Once the pump start running (just a few seconds) the unloader doesn't matter. I mean if it's open it will take longer to fill up but it will still fill up. If it's closed... well it's supposed to be closed when the pump is running.

BTW, a picture of your system showing the pumping between the pump, pressure switch and tank would be helpful.

(note: in my compressor the unloader line connects right next to the In Tank Check Valve vs at the pump head)

Thanks - I put the new pressure switch on and it is shutting off at around 135psi. Not sure but the gauges might be off a little. I had that unloader valve line off when I put the new switch/unloader valve on but am going to remove it again and make sure it is not obstructed. I have been running it without a filter on the air intake for some time. I will listen for the hiss and upload a pic. When the compressor tries to start, it does turn over a couple of revolutions, stops, turns over a couple more revolutions and stops again. At that point, the breaker has popped.

 

[Buckaroo5]

a reasonable explanation on you tube

Thanks but I have the new pressure switch that has a new unloader valve on it so would think that is not the problem. I was thinking maybe you were suggesting a second parallel unloader valve but really can't plumb that in. The unloader valve is integrated into the pressure switch.

 

[Buckaroo5]

OP, I think you may have two problems. Let's start with not getting past 120 psi. If the motor runs fine until we get to 120 psi then the pressure switch shuts things off, that's just a pressure switch that needs to be adjusted. Many of these switches look the same but may be factory preset set to different pressure levels. Not hard to adjust the screws. However, if your problem is the pump keeps running but can't build pressure past 120, that could be a bad valve in the pump itself. A classic reed valve failure is the pressure builds slowly then can't get past some limit. If that is your issue then you need to pull the head off the pump.

The next thing is why can't you restart the pump. That sounds like an issue with the unloader valve not working correctly. Since that valve is typically part of the new pressure switch, I doubt it's broken but maybe it's connected wrong or not at all. Somehow the pressurized air in the pump to tank interconnect is not getting drained after the pump shuts off. Unloader valves are very simple so I think it's unlike to be broken. But it's possible the line is not connected correctly. Do you head a sudden psss of air just after the pump turns off? If no, then it's probably connected wrong. Note that even if the valve never opened, air will naturally leak out of the pump to tank interconnect via the valves in the pump head. However, if might take many minutes to reduce the pressure enough for the pump to restart. This is why you could restart the pump the next day but not while in use. Also, the unloader valve only affects starting the pump. Once the pump start running (just a few seconds) the unloader doesn't matter. I mean if it's open it will take longer to fill up but it will still fill up. If it's closed... well it's supposed to be closed when the pump is running.

BTW, a picture of your system showing the pumping between the pump, pressure switch and tank would be helpful.

(note: in my compressor the unloader line connects right next to the In Tank Check Valve vs at the pump head)

 

[The Cobbler]

the unloader on the switch does (should) unload the line. this allows a bit more time for the motor to get up to full speed before hitting compression . it is an add on and might be beneficial in your case

 

[Buckaroo5]

OP, I think you may have two problems. Let's start with not getting past 120 psi. If the motor runs fine until we get to 120 psi then the pressure switch shuts things off, that's just a pressure switch that needs to be adjusted. Many of these switches look the same but may be factory preset set to different pressure levels. Not hard to adjust the screws. However, if your problem is the pump keeps running but can't build pressure past 120, that could be a bad valve in the pump itself. A classic reed valve failure is the pressure builds slowly then can't get past some limit. If that is your issue then you need to pull the head off the pump.

The next thing is why can't you restart the pump. That sounds like an issue with the unloader valve not working correctly. Since that valve is typically part of the new pressure switch, I doubt it's broken but maybe it's connected wrong or not at all. Somehow the pressurized air in the pump to tank interconnect is not getting drained after the pump shuts off. Unloader valves are very simple so I think it's unlike to be broken. But it's possible the line is not connected correctly. Do you head a sudden psss of air just after the pump turns off? If no, then it's probably connected wrong. Note that even if the valve never opened, air will naturally leak out of the pump to tank interconnect via the valves in the pump head. However, if might take many minutes to reduce the pressure enough for the pump to restart. This is why you could restart the pump the next day but not while in use. Also, the unloader valve only affects starting the pump. Once the pump start running (just a few seconds) the unloader doesn't matter. I mean if it's open it will take longer to fill up but it will still fill up. If it's closed... well it's supposed to be closed when the pump is running.

BTW, a picture of your system showing the pumping between the pump, pressure switch and tank would be helpful.

(note: in my compressor the unloader line connects right next to the In Tank Check Valve vs at the pump head)

If I try and start it at 80 psi rather than 120 psi, it chugs, stops, chugs again, stops, chugs again, stops and keeps repeating without popping the breaker. I did check the line from the unloader valve to the backflow valve and it is clear. Also, I am hearing the hiss at shutdown. I was hearing that even before I replaced the switch/unloader valve (which was why I first replaced the backflow valve). I am going to go back at the capacitors again.

 

[Buckaroo5]

OP, I think you may have two problems. Let's start with not getting past 120 psi. If the motor runs fine until we get to 120 psi then the pressure switch shuts things off, that's just a pressure switch that needs to be adjusted. Many of these switches look the same but may be factory preset set to different pressure levels. Not hard to adjust the screws. However, if your problem is the pump keeps running but can't build pressure past 120, that could be a bad valve in the pump itself. A classic reed valve failure is the pressure builds slowly then can't get past some limit. If that is your issue then you need to pull the head off the pump.

The next thing is why can't you restart the pump. That sounds like an issue with the unloader valve not working correctly. Since that valve is typically part of the new pressure switch, I doubt it's broken but maybe it's connected wrong or not at all. Somehow the pressurized air in the pump to tank interconnect is not getting drained after the pump shuts off. Unloader valves are very simple so I think it's unlike to be broken. But it's possible the line is not connected correctly. Do you head a sudden psss of air just after the pump turns off? If no, then it's probably connected wrong. Note that even if the valve never opened, air will naturally leak out of the pump to tank interconnect via the valves in the pump head. However, if might take many minutes to reduce the pressure enough for the pump to restart. This is why you could restart the pump the next day but not while in use. Also, the unloader valve only affects starting the pump. Once the pump start running (just a few seconds) the unloader doesn't matter. I mean if it's open it will take longer to fill up but it will still fill up. If it's closed... well it's supposed to be closed when the pump is running.

BTW, a picture of your system showing the pumping between the pump, pressure switch and tank would be helpful.

(note: in my compressor the unloader line connects right next to the In Tank Check Valve vs at the pump head)

My run capacitor labeled 30 micro farads tests 29.8. My start capacitor labeled 136-163 micro farads tests at 149. I am out of things to check. Pic of start capacitor follows

 

[Buckaroo5]

New info for me....I think I have to unsolder the bleed resister to get a good test on the start capacitor so going to do that and retest.

 

[Citation]

Do you know if all the ports on the pressure switch are tied together?
To verify the unloader isn't an issue you could try cracking open the fittings so it bleeds out air. That will slow down the filling rate a bit but if the unloader is the problem this would prove it.

Being an oil free compressor I would really want to know if the piston ring is bad. A bad ring would show/prevent it from filling.

You might have a bad check valve. However, I think it would have to be very bad to keep the pump under pressure. Does the compressor hold air when shut off? Like over 24 hr does the pressure hold? If yes then the check valve isn't likely bad. This is definitely true if you know the unloader is working.

 

[Buckaroo5]

Do you know if all the ports on the pressure switch are tied together?
To verify the unloader isn't an issue you could try cracking open the fittings so it bleeds out air. That will slow down the filling rate a bit but if the unloader is the problem this would prove it.

Being an oil free compressor I would really want to know if the piston ring is bad. A bad ring would show/prevent it from filling.

You might have a bad check valve. However, I think it would have to be very bad to keep the pump under pressure. Does the compressor hold air when shut off? Like over 24 hr does the pressure hold? If yes then the check valve isn't likely bad. This is definitely true if you know the unloader is working.

Did just replace the check valve before I did the switch/unloader so likely good. I am pretty sure that the unloader is not tied to the other three ports. The compressor holds air well and once the motor gets started, it fills well. I won't have time to do any more work on it until Sunday/Monday so will update then with what I find on the start capacitor. I plan on desoldering that bleed resistor and retesting the capacitor and the resistor itself. I really think that has to be the problem.

 

[Citation]

Did just replace the check valve before I did the switch/unloader so likely good. I am pretty sure that the unloader is not tied to the other three ports. The compressor holds air well and once the motor gets started, it fills well. I won't have time to do any more work on it until Sunday/Monday so will update then with what I find on the start capacitor. I plan on desoldering that bleed resistor and retesting the capacitor and the resistor itself. I really think that has to be the problem.

The unloader shouldn't be tied to the others. It's basically just a vent to the atmosphere when opened. I wonder if the check valve is just broken. Consider this. If the check valve was broken you would very quickly run the pressure in the interconnect to well over the max pump pressure. That could cause the motor to stall very quickly. However, the pressure gauge, which is measuring the tank pressure, not the interconnect pressure, would read something lower. It's not an expensive part and might be worth loading into the parts cannon.