Craftsman 6Hp/30 gal - can't recharge w full tank

4 years 5 months ago #1629 by FLAir5

Sears Craftsman Model# 919.165130 6HP, 30 gallon - This thing is driving me insane. Motor starts effortlessly, and fills to about 125psi. When the air pressure drops to trigger a recharge, the motor struggles, barely turning over, then eventually trips the breaker. So I took to researching the problem. Most things pointed to an unloader valve gone bad. However, if you go to Sear's parts site, it tells you the problem is a bad check valve. So I replace the check valve. Sam problem, they tell me "well, then it can only be the pressure switch" (which are not cheap for this unit). So I just get done replacing the pressure switch, was all excited, and exact same problem!!

There are no leaks, everything seems connected fine. The unloader valve seems to be part of the pressure switch that I replaced - so with new parts on these, am I missing something? Can the problem lie elsewhere? When this all started, I thought maybe the issue was that I was running it in my shop (home) off of a 15amp 120v breaker, and maybe that wasn't enough...but that doesn't explain that is starts with an empty tank fine, and the pressure should be off of the head, and restart fine as well if everything is functioning as it should??!!

Any suggestions or help are greatly appreciated!

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4 years 5 months ago #1630 by MTR-Admin

Thanks for the post!

I cant' blame you for being frustrated, this symptom can be caused by many potential problems so it's irritating to say the least when it still occurs when you've dumped a decent amount of money into it.

Initially I would have said the same thing, your Check Valve is sticking open after the unit shuts off, thereby putting back pressure on the Head and causing the breaker to trip, but that's obviously not it.

Sure, the Unloader Valve on the Pressure Switch can cause this to happen as well, but you've replaced this also. Just to confirm, when the unit reaches 125 PSI and shuts off, does the Unloader Valve actually blow off and unload the air like it's supposed to? Let's make sure that is actually happening, firstly.

The only other reason this could be happening is due to an electrical issue, but I doubt it.

Make sure there is no debris in the Discharge Tube, which connects the Pump to the Tank inlet. You may have had some debris sucked through the intake that's keeping the check valve open, which can cause this.

I'll try to get some additional info and reply.

- MTR

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4 years 5 months ago #1631 by FLAir5

Thanks for the quick reply MTR! Hmm... so the discharge tube - is that the silver tube with compression fittings on both ends that runs from the check valve to the unloader? If so, the new switch came with new compression fitting and nut, so I went to trim the old one off, and like a dumb a@#, used a pair of nippers, which of course crimped it. I then got a small hacksaw and trimmer it properly, and sanded off the rough edges. Again, not sure if I even have the right line here, but if there was any possibility of metal fragment (I don't think so, but possible for sure) in that line, that could cause this? Thanks!

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4 years 5 months ago #1632 by MTR-Admin

No problem :)

You can inspect the Unloader Line you're referring to, sure, but I was referring to the larger (3/8" or 1/2" OD) Transfer Tube that connects from the outlet of the pump head to your tank (Check Valve); this carries the bulk of the air to the receiver tank. It should also have compression fittings on either end.

It's possible some debris was sucked into the intake filter of the head and is causing your Check Valve to stick.

It is also possible that this is an electrical issue with the motor.

If this motor has both a starting and a running capacitor then it is possible that there is a problem with the starting capacitor (the cylindrical object located under the motor shroud, usually bolted onto the top of the motor) or the connections to it.

There is a centrifugal switch located inside the motor that opens and closes to transfer connection to and from the start and run capacitors. If this switch is sticking or not making a connection when the motor stops then the start capacitor will not be connected in the circuit for start up of the motor. I would make certain that there is not a back pressure issue by running the unit up to pressure and removing the discharge line from the compressor pump head. If air leaks out of the Discharge Line from the Check Valve after it shuts off, then you the Check Valve is sticking.

If the unit still will not start then I would proceed to checking the motor connections, capacitors and switch.

Hope this helps!

- MTR

The following user(s) said Thank You: FLAir5

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4 years 5 months ago #1641 by FLAir5

Just now getting back to this. Wow...this is getting more complicated than I thought. Ok, so I pulled the motor shroud off, disconnected and inspected the discharge line, and just blew everything out with my functional pancake compressor. When you mentioned getting the tank up to pressure, then removing the discharge line from the head...obviously that line should not be under pressure when the unit is idle and the tank full, right? Thanks

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4 years 5 months ago #1642 by MTR-Admin

That's correct. Since the Transfer/Discharge Tube is connected to the Check Valve, which is installed into the tank inlet, you should not get ANY air back-feeding from the Check Valve and through the Tube.

The Check Valve should stay closed while the unit is off. If you get any air leaking back, the Check Valve is the problem. If no air back-feeds through the Tube, the problem lies elsewhere.

- MTR

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