# Graco 390 sprayer motor straining



## boil2win (Dec 29, 2013)

Pump primes fine, but when I switch to spray, the motor struggles. The motor never stops, but it sounds like it's going to burn up. This is whether I'm cleaning with water or using paint. 

I had it packed with oil for the last year. I primed it with latex last week, but when I switched to spray, it kept leaking from prime tube. I came back the next day to work on it, but it worked perfectly. I primed 100 boards of sheetrock without one problem. 

Today I was setting up to spray more primer and it primed up fine, but would never run right on sprayer mode. I'm wondering if the pressure control is part of the problem.

Thanks,
Boil2win


----------



## MikeCalifornia (Aug 26, 2012)

You have something stuck in the intake ball area. When you switch to paint, the pump should build to the pressure you set then the motor will stop. You might need a new prime valve also, if it is leaking out the prime tube when switched to spray. Also remember to put some piston lube in each time you spray.

I had a similar problem to yours, but the pump intake filter screen was clogged and it just could not suck paint. I cleaned and it was fine.


----------



## RH (Sep 7, 2010)

If what Mike says doesn't work then go to Lowes and buy a LTS 17.


----------



## driftweed (May 26, 2013)

If all else fails turn it upside down and whack it with a hammer. Seriously cannot believe that is a solution listed on graco's website, lol.

Be careful, if you spank the sprayer it's gonna have firehose style pressure and will kick like a mule. It gets pissed when you spank it like the bad boy it is.


----------



## boil2win (Dec 29, 2013)

Thanks guys. I changed the prime valve out and repacked the pump. It still does the same thing -- primes fine, then when I switch to spray, it pumps and pumps until it releases from the prime tube. It builds a lot of pressure. Even with the pressure turned all the way down, it pumps up like crazy. Anyone know what the symptoms of a bad pressure control switch are? And if the pressure built up too much, would it release through the prime tube?


----------



## robladd (Nov 22, 2010)

Sounds to me that the potentiometer/pressure control switch is shot. Good thing the dump valve is working. That's a good way of blowing a hose or pump.


----------



## boil2win (Dec 29, 2013)

Is there a way to check if it is the pressure control switch or the control board? Do you know if the switch is supposed to be open or closed at high pressure?


----------



## Oden (Feb 8, 2012)

boil2win said:


> Is there a way to check if it is the pressure control switch or the control board? Do you know if the switch is supposed to be open or closed at high pressure?


I never had a pressure switch problem yet but my ges would be open when not calling for the motor to come on.Id think a call for pressure would connect the wires and make the motor come on and I'd think to test the switch I'd detach, jump and unjump the leads to see what it does.


----------



## RH (Sep 7, 2010)

Piston rod could be scratched also. If your filters happen to be blown when the packings go it can let particles in that scratch the rod when it's pumping up and down. Any little scratch can keep pressure from building.


----------



## mr.fixit (Aug 16, 2009)

sounds to me like a bad seat. Prime the unit and when it is primed close the prime valve and turn down the pressure control until the unit stops. then turn it up a very little and watch if the piston drifts up or down. If it drifts down the bottom seat is bad remove it and flip it over they are reversible and if the piston drifts up the piston seat is bad and is reversible as well. you have to remove a graco piston and it does not have a reversible seat you would need to change the piston valve which is the piece that the packings go on


----------



## Oden (Feb 8, 2012)

boil2win said:


> Thanks guys. I changed the prime valve out and repacked the pump. It still does the same thing -- primes fine, then when I switch to spray, it pumps and pumps until it releases from the prime tube. It builds a lot of pressure. Even with the pressure turned all the way down, it pumps up like crazy. Anyone know what the symptoms of a bad pressure control switch are? And if the pressure built up too much, would it release through the prime tube?


I don't think anyone really reads theists sometimes. Or it could be me. but. ain't the guy saying he has pressure. And more than he wants. He already did some work he didn't need to do. IF he is building pressure his piston and pax kings are Kool. Is what I'd think.


----------



## boil2win (Dec 29, 2013)

Thanks Oden


----------



## Oden (Feb 8, 2012)

every pump I ever used the pressure nob if turned all the way down is for practical purpose also a 'off' nob. The pump won't come on if turned all the way down. If the nob is all the way down and the pump is coming on something must be wrong with the switch IMO. the pressure switch, though, is I beleive wired through a circuit board in some way. And once it hits a circuit board my diagnostic ability stops.


----------



## Bender (Aug 10, 2008)

Oden said:


> I don't think anyone really reads theists sometimes. Or it could be me. but. ain't the guy saying he has pressure. And more than he wants. He already did some work he didn't need to do. IF he is building pressure his piston and pax kings are Kool. Is what I'd think.


My God. Are you typing on an ipotato?
:laughing:


----------



## SprayRepairGuy (Jan 15, 2014)

boil2win said:


> Thanks guys. I changed the prime valve out and repacked the pump. It still does the same thing -- primes fine, then when I switch to spray, it pumps and pumps until it releases from the prime tube. It builds a lot of pressure. Even with the pressure turned all the way down, it pumps up like crazy. Anyone know what the symptoms of a bad pressure control switch are? And if the pressure built up too much, would it release through the prime tube?


Since you are building pressure to the point that the prime/spray valve releases, I don't think you have bad seats, bad packings, or a scratched rod causing the problems. *Your pressure control surely is not controlling. * The fluid getting released through the return tube back to the bucket is normal for an overpressure. The prime/spray valve is spring loaded and designed to release as a safety feature when an overpressure occurs at about 3600 PSI. My guess is that your transducer and/or pressure control need replacing. They simply are not detecting the increased pressure and should be telling the motor to turn off. This is also why your motor is straining - you have too much pressure.


----------



## mr.fixit (Aug 16, 2009)

I guess I did not read the post correctly the first time. If it is pushing through the drain hose after the prime valve is closed at full pressure then Spray Repair Guy is correct it is either the transducer or the circuit board.
The circuit board is warranted for 4 years the transducer for 1 year. If you have an electrical problem which this is I recommend a service center. If the unit is older than 4 years have them give you an estimate before any repairs are done


----------

