Tools, Sharpening and Power Machinery - Air compressor won't shut off...

Howdy...

I inherited my dad's Grainger 150psi compressor. It's wired for 220v...I have three problems with it:

First, it doesn't shut off...the motor just bogs down and gets slower and slower. Power continues to be applied until I unplug it.

Second, even after it starts to bog down a lot, it's not to full pressure. I only get around 40psi out of it.

Third, there is voltage present on all metal parts of the compressor. I know this will need to be addressed by an electrician.

I have read all the other threads here on problems like this. As a result, I have replaced the pressure switch, the pop-off valve, and the unloader valve. I also replaced the regulator and valve there, as well as the wiring and wired it exactly the same (the old wire was just wrapped in electrical tape and didn't look very safe). The wiring I used is industrial grade 4 conductor, each conductor is 12ga. The electrical shop I bought it from pulled out a little calculator and said the wire would be fine for a 220vac 2hp motor.

Please be kind...I haven't messed with compressors much before now. I know it'd probably be better to just go buy a new compressor but this was my dad's and it has sentimental value to me. And it appears to be in decent shape...especially since I've replaced many of the parts on it.

Any help would be much appreciated...thanks!

JM-99

Jumpmaster,

What jumps out at me is the possibility that the motor is wired for 220 volts but it is only getting 120.
This describes your symptoms perfectly.
If you are using a 220 volt plug did you wire it?

If you look into this and come back with the Grainger model number we can dig deeper.

You have rewired it and it still represents a shock hazard? Something about the wiring is not correct then. Since it's from Grainger, it's probably a Dayton (or maybe a Speedaire) compressor.

There are compressor repair shops. Locate your nearest supplier to the house framing contractor trade. They usually service compressors as well as nailers and selling nails for building houses.

You might also contact Grainger to see if they can find an owner's manual as well as a schematic. You mention an unloader valve. Those are typically only used with gasoline rather than electric motors. If this compressor was manufactured with an unloader valve, then converted to electric power, the motor SHOULD run all the time (just like a gasoline engine would). The unloader should open up when 120-150 psi is reached to vent the compressor output and quit trying to put more pressure into the tank. When the tank pressure drops, the unloader closes to resume pressurizing the tank.

Thanks for the help, Folks...

The compressor has diagrams for wiring for both 220 and 110. It's currently wired for 220 and since we don't have a 220 outlet in the garage, it gets plugged into the dryer outlet.

I just checked...The model is a Speedaire 3Z189B single stage.

There's a diagram on the motor for wiring (it's a Dayton motor)...later tonight, I will transcribe the diagram and post it here.

About the unloader valve...well, I don't really know what it's proper name is...a friend of mine that used to repair compressors years ago told me to check it and that's what he called it...the one I thought he was talking about was the valve that goes from the pump to the tank. You all probably already know how my tank is arranged, but there's a tree that has three outlets on it that comes out of the tank...the pressure switch on one, the pop-off valve on the other one, and a 90° elbow that goes to this valve on the third.

You guys are awesome...I'd be happy to know half of what y'all know about this stuff! :)

JM-99

jumpmaster,

The component that is located between the compressor and the tank is the check valve.

The two possibilities are that the motor is bad or the unit is wired wrong.
You will need to double check the connections and use a tester to figure out if the motor is receiving the proper voltage.

What were the symptoms before you started replacing parts?

Symptoms before were the same as now...motor bogs down...very low air pressure produced...motor never shuts off.

Starting to sound like it's been wired wrong since my dad had it...:(

I need to check, but it has wire T2 and T8 from the motor are wired together...I'll have to go out there and get the diagram I made and report back...

Thanks!

JM-99

Ok...here's how it's hooked up now:

If you're viewing the switch with the adjustment screw to the top (away from you) using the terminals L1, T1, L2, T2 from left to right as follows...
The "O" is the screw holding the cover on...

O
| L1 | T1 | L2 | T2 |

Black from the power cord goes to L1, white from the power cord goes to L2.
T8 and T4 from the motor go to T1 on the pressure switch. T1 from the motor goes to T2 on the pressure switch.

The diagram on the motor for 220vac is as follows:

T1 | T3 T8 T2 | T4 T5
_____ | ________ | _______
Line | Tape(?) | Line


Below this, it states for CCW rotation (which the compressor specifies it is), interchange T5 and T8. Sorry I couldn't get the diagram to look right...under T1, it says "Line"...under T3, T8, and T2, it says "Tape"...under T4 and T5, it says "Line".

I'm not an electrician...obviously. :) As such, I'm completely baffled...but I reckon you already knew that. :)

Thanks again for your patience and help...I'm sure whatever the problem is will just be jumping out with neon signs to those of you that understand this.

JM-99

Could it be the actual windings on the motor itself. Sounds like there is a short somewhere[windings].

"Third, there is voltage present on all metal parts of the compressor. I know this will need to be addressed by an electrician."


Is this capacitor start. Maybe check some resistances if it is, this will tell you if there is a short in the windings. Discharge capacitor first. Are you using and extension cord at all. If so don't.Does the motor get hot when bogging down. There should be a thermal switch in the motor that shuts it off.



Not an electrician but these are some things I would check



does it look like one of these


http://www.electricmotorwarehouse.com/IMAGES/B381_connection.htm

jumpmaster,

According to the motor diagram one of the hot wires from the pressure switch should be connected to the T1 terminal. The other hot wire should be connected to T4 and T5. T2, 3 & 8 should be twisted together and not connected to anything.

Honestly, no clues as to what is wrong will jump out untill we hear what some of the voltage readings are at various connections.
I will assume that you know "there is voltage present on all parts of the machine" because you get a shock when you touch it, not from a meter reading.

A bad motor or wrong wiring are the two most likely causes of your problem.
If you are getting a shock from the touching the machine then this would be from either a serious wiring mistake or the motor windings going AND an improperly wired ground.
The ground wire should be firmly attached to the frame where the cord is connected which is usually in the pressure switch. Another wire should be joined to this connection and then carry on to the motor and then be connected to the frame of the motor where the other wires connect.


If you were able to take some close up photos of the wiring and find a host we could look at the wiring but without having this and voltage readings to be sure you have 220 volts getting to the motor, there is really no more that I think we can offer.
Diagnosing problems is not a guessing game.
I would strongly suggest you hire someone who is familiar with wiring to properly check this out for you before someone gets hurt..

Ok, thanks.

Bye.

It sounds like a bad capacitor or the centrifugal switch located in the back end of motor.
Mike A

This is a less likely problem but a broken exhaust valve in the pump unit could cause a bogging motor that wont build PSI or shut itself off.

Not sure why its building up a voltage, but when a condition like that does happen the ground wire is supposed to take care of it. Check the ground wire itself, where it connects to the motor and also check the outlet.

It could be possible that you have a gound issues in your home. If your house is 30-40 years old then you may not have a common gorund and your getting a feedback from a bad winding. Thing is, that shouldnt cause the motor to act the way it is. Only thing it might do is cause the leaking voltage.

Hear is an odd question (and I seriously doubt it possible), but did you dad order this item unit as an import? If it's made for europe then you would have to have a step-up transformer to run it. They are 240v at 50 hz and that could cause a motor collapse if you keep trying to run it at 220 60hz.

I really doubt that idea would help, but if nobody has checked then it is possible and may be of some use. Good luck.