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Old 01-02-2011, 06:05 PM   #1
sigtauenus
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Default Problem - slow starting air compressor

This is really weird. Video is about 1 min long. Shows how the air compressor will kind of "wind up" as it is going. It starts right away but has a really slow rpm that builds gradually. It almost seems like its not lubricated but the sight gauge shows it is full of oil.

Compressor is a Campbell Hausfeld VT627505AJ. 60 Gallon tank, 230V, 3.2 HP.

It is about 2 years old and has previously worked fabulously.

http://www.youtube.com/watch?v=4GQUzWpcmvY

As you're watching the video, there is some noise from the motor but you can kind of tell the clunky slow start of the compressor about 15 seconds in, particularly as it starts smoothing out.

Any ideas? I bought it at Lowes, and am tempted to scour my desk for the receipt and take it back and exchange it but if the fix is reasonable I'd rather just fix it than haul a big a$$ compressor to Lowes and back.
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Old 01-02-2011, 06:17 PM   #2
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Default Re: Problem - slow starting air compressor

start capacitor would be my guess. Have you cracked loose the air line between the pump and the tank check valve to be sure the pump isn't starting under load?
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Old 01-02-2011, 06:22 PM   #3
sigtauenus
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Default Re: Problem - slow starting air compressor

I have not. Clarify what I'm looking for? If I hear a hiss that means the pump is under load, right? Would that be a bad check valve?

This just started about a week ago when it got really freaking cold here.
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Old 01-02-2011, 06:28 PM   #4
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Default Re: Problem - slow starting air compressor

Correct. The way *most* compressors work, is that there's a check valve between the pump and the tank. However, this obviously still leaves pressure in the pump when it shuts off, so the pressure switch usually has a bleed off valve on it, that bleeds the pump pressure off for a few seconds when the pressure switch shuts the motor off, then the valve closes again.

It's possible that valve on the pressure switch isn't working either, but...I assume your compressor has sat for a while before you've tried starting it, in which case, the pressure would still have bled off (albeit, slowly).

Most motors have a start capacitor on them to help them get up to speed, so I'm guessing it's either that, or the check valve is leaking, and letting tank pressure back into the pump.
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Old 01-02-2011, 06:30 PM   #5
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Default Re: Problem - slow starting air compressor

Is it in a cold garage Sig? Did you notice the problem when temps recently dropped? Does it reach speed as it warms up and runs a bit? It's a pretty common condition in cold temps from thick earl.
My old Sanborn will trip the circuit a couple times a year when chilly. Same symptoms.
I agree that junk/flakes in the check valve will do it too as pump is pushing against tank pressure if it doesn't seal.
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Old 01-02-2011, 06:31 PM   #6
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Default Re: Problem - slow starting air compressor

Quote:
Originally Posted by nissan_crawler View Post
Correct. The way *most* compressors work, is that there's a check valve between the pump and the tank. However, this obviously still leaves pressure in the pump when it shuts off, so the pressure switch usually has a bleed off valve on it, that bleeds the pump pressure off for a few seconds when the pressure switch shuts the motor off, then the valve closes again.

It's possible that valve on the pressure switch isn't working either, but...I assume your compressor has sat for a while before you've tried starting it, in which case, the pressure would still have bled off (albeit, slowly).

Most motors have a start capacitor on them to help them get up to speed, so I'm guessing it's either that, or the check valve is leaking, and letting tank pressure back into the pump.
Very Well Described NC.... I had a similar problem and after some testing it ended up being the Starting capacitor, Just took the old one off and matched it up at the local small engine shop.
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Old 01-02-2011, 06:34 PM   #7
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Default Re: Problem - slow starting air compressor

Yes, its in an uninsulated garage. And yes, the problem started a week or so ago when the winter storm hit the east coast.

I recently changed the oil too, it had gotten pretty dark in the sight glass, and I replaced it with 30W non-detergent oil, same stuff I use in my generator.
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Old 01-02-2011, 06:35 PM   #8
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Default Re: Problem - slow starting air compressor

Thanks for all the quick replies gents.

Is this starting capacitor a motor part or pump part? I assume its on the motor.
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Old 01-02-2011, 06:36 PM   #9
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Default Re: Problem - slow starting air compressor

It's possible it's the oil, but that being said, our compressor was left on 24/7 for 20 years in an uninsulated shop that saw -30F, and never had an issue. Even worse, I'm fairly sure that oil was maybe changed once, if at all.

If you want to be sure, drain the oil and put it in your house for a while. Then fill it up quick and flip it on. Hey, it worked for Model A's.
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Old 01-02-2011, 06:42 PM   #10
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Default Re: Problem - slow starting air compressor

Quote:
Originally Posted by sigtauenus View Post
Thanks for all the quick replies gents.

Is this starting capacitor a motor part or pump part? I assume its on the motor.
correct.

http://www.ehow.com/how_4473927_test...capacitor.html

Just be careful with it, a good zap from the cap can knock you dead (not likely, but don't mess around, either).
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Old 01-02-2011, 06:43 PM   #11
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Default Re: Problem - slow starting air compressor

Is your wiring on a dedicated, at least 20 amp circuit with nothing else trying or working at the same time? Not aluminum wiring or some old, old wiring? I would check the check valve, located, where the dump tube feeds the tank, this thing could have partially let go, releasing pressure back on the head and not letting it start, if it does go out it will not start up at all?!
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Old 01-02-2011, 06:52 PM   #12
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Default Re: Problem - slow starting air compressor

Thanks again for the replies.

Found the capacitor on the motor. Actually looks like there is two of them, one is white, the other black. I have a neighbor who is an electrician so I'll have him come over tomorrow and test it for me. He'll probably also know of a local shop where I can replace the capacitor if its bad.
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Old 01-02-2011, 06:53 PM   #13
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Default Re: Problem - slow starting air compressor

Oh yeah, wiring is on a dedicated 240V, 30A circuit.
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Old 01-02-2011, 06:58 PM   #14
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Default Re: Problem - slow starting air compressor

Most compressors use 20w oil, which would be thinner than 30w. My contractor compressor won't start when it is cold, but if you carry it in the garage it fires right up.
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Old 01-03-2011, 01:39 AM   #15
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Default Re: Problem - slow starting air compressor

I would also check the bearings in the motor. The grease may not be up to the cold temperatures.
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Old 01-03-2011, 01:56 AM   #16
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Default Re: Problem - slow starting air compressor

My compressor did almost that exact same thing. Replaced both capacitors on general principles, no fix. Cleaned the centrifugal switch, bingo, problem solved. You can google how to find it, but basically if you pull the end cap off the motor you will see a switch that is activated by weights swinging out as the motor spins up, you can clean the little contact areas by dragging a piece of alcohol soaked cardstock (I use a business card) between the contacts. Note the carbon and grease on the paper. Do it again until the paper is clean.

Last edited by Warrenator; 01-03-2011 at 01:57 AM. Reason: spelling
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Old 01-03-2011, 02:43 AM   #17
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Default Re: Problem - slow starting air compressor

Quote:
Originally Posted by sigtauenus View Post
Yes, its in an uninsulated garage. And yes, the problem started a week or so ago when the winter storm hit the east coast.

I recently changed the oil too, it had gotten pretty dark in the sight glass, and I replaced it with 30W non-detergent oil, same stuff I use in my generator.
Your "caps" are fine.
Try pouring some of that 30w oil into a cup, at 15deg. F.
Like honey, aint it?
I changed to synthetic, Got tired of using a "heated dipstick"
Search "compressor oil" You'll find a ton of info.
Watching your vid the check valve is ok too.
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Old 01-03-2011, 09:21 PM   #18
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Default Re: Problem - slow starting air compressor

Unloader valve: When the set pressure is reached, and the motor is shut down,the unloader releases pressure on the pump (upstream of the check valve on the tank) so the motor/pump doesn't have to start against pressure.

It's the first thing I'd check....
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Old 01-04-2011, 05:49 AM   #19
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Default Re: Problem - slow starting air compressor

The oil is to thick for the temperature you are running in.
Head unloader is working fine, you can hear the air being relieved.
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Old 01-07-2011, 11:03 PM   #20
sigtauenus
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Default Re: Problem - slow starting air compressor

Thanks for the replies.

Been busy and out of town. Several cheap or free and easy suggestions. Still need to check the capacitors, will also clean the centrifugal switch and try some synthetic oil.

If I go synthetic, should I also go to a thinner 20W?
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