Air Compressor Pressure Switch Wiring SNAFU

[89MustangGX]

I recently picked up a new air compressor, unfortauntely I couldn't hear it run before I bought it.

http://garagejournal.com/forum/showthread.php?t=47343

The seller assured me it was a great unit, and it looked good except for a couple minor things, so I bought it. Hopefully I didn't make an error in judgement.

I could see it had the wrong plug on it (15 amp plug, requires a 30), and cord had been spliced at least once, so I planned on replacing the cord anyway.

I am fairly new to the 240v scene, but I am learning. I finally got around to opening up the pressure switch so I could get into changing the cord so I can finally run it and I am a little upset at what I see. I can post pictures, but let me try to explain and see if this is enough.

From what I gather -- the pressure switch has 4 terminals, and 2 grounds. 2 hots and a ground in from supply, and 2 hots and a ground out to the motor. Seems basic enough, and this is what the wire diagrams on the cover of the switch seem to show.

What I found:

*Grounds from supply and ground from motor connected independantly to ground screws on switch. Ok.

*White wire from supply to terminal on switch. White wire from motor to terminal on switch. Ok.

*Black jumper wire made up to connect the other two terminals on the switch together. Oh boy.

*Black wire from supply wire nutted to black wire from motor. Uh oh.

At this point I paniced a little and started trying to figure out exactly what was going on. I checked and I have continuity between the pairs of terminals on the switch with each other when turned on, and not when switch is turned off. (Meaning the switch appears to connect the two supply leads to the two motor leads when closed.) This is about as much as I think I can check without fixing this and putting power to it.

I think having it wired the way it was allowed 120v constant to the motor and the pressure switch was switching 120v on and off.

My questions are:

*Am I right about how this SHOULD be wired?

*Would this have damaged anything? Pressure switch, motor, etc?

*Why would this be done? Is this an indication of a bad pressure switch or something? Or is this just a hack job fix for something?

*Is there anything I can check to see if everything is ok before I fix this and put power to it?

Thanks in advance!

Adam

 

[GeorgiaHybrid]

You should be OK. The pressure switch is wired 120 volt to run the mag starter. It will switch the mag starter on or off depending on the pressure and let 240 volts go to the motor.

 

[89MustangGX]

I don't think this compressor has a mag starter on it -- the wiring goes direct from the supply to the pressure switch to the motor.

I'm reasonably sure that someone has gone in and messed around with the wiring -- it definitely doesn't match what's shown on the diagram on the lid of the switch.

Adam

 

[Gary S]

If I understand your description of the wiring correctly, it sounds to me like someone bypassed the pressure switch with the black wire. Look at the contacts. You might find them burned enough that they could have been causing problems and the switch was bypassed.

 

[GeorgiaHybrid]

What HP is your motor? 3HP or less and the pressure switch will work OK. At 5HP, the mag starter can/should be used but is not a requirement. A 7.5 HP and up motor needs a mag starter.

If yours does not need a mag starter, wire your two hots and ground into one side of the switch and the two hots and ground to the motor on the other side. Check to see if your motor is reversable and watch to make sure you have it turning in the right direction. That info should be on the motor.

Just to make sure, can you post some pictures of what you have? There are several guys on here that know a LOT more about wiring than I ever will and it never hurts to get someone else to take a look at it.

 

[tigmusky]

wow with out pics this is hard. I"ll try
#1 look on the side of the elec motor. There should be a diagram low volts/120 and 220/volts. Alot of these motor have dual voltage. meaning you can run them on a 120 or 220 circuits. It all depends on how the motor is wired inside. this is what the diagram is for... it should say something like yel and org to tem 2 or something.

#2 once we know what its wired for or what you want it wired for then we can wire the pressure switch

#3 pressure switch...Is just a light switch on/off motor/load and power/common

take a look If you can pics will help a ton. if you still have troubles send a pm and swamp phone# I should be able the walk you thought it

Daye

 

[tigmusky]

sorry I just saw the pics.. Now lets see a pic of the inside of the pressure switch

a.o. smith motor man. tank and I tie pump

Daye

 

[89MustangGX]

If I understand your description of the wiring correctly, it sounds to me like someone bypassed the pressure switch with the black wire. Look at the contacts. You might find them burned enough that they could have been causing problems and the switch was bypassed.

Yes -- this is how I believe it is currently wired. The contacts on the switch look ok to me, but it looks like the spade terminal on one of the wires got hot. I am suspecting this may be a hack fix for a melted spade terminal problem.

What HP is your motor? 3HP or less and the pressure switch will work OK. At 5HP, the mag starter can/should be used but is not a requirement. A 7.5 HP and up motor needs a mag starter.

If yours does not need a mag starter, wire your two hots and ground into one side of the switch and the two hots and ground to the motor on the other side. Check to see if your motor is reversable and watch to make sure you have it turning in the right direction. That info should be on the motor.

It is a 5hp motor. Rated 22amp.

It didn't come with a mag started originally, so unless it really definitely needs one, I'd rather not add it.

I believe what you're describing for wiring is how I think it should be wired -- so we are on the same page.

Now lets see a pic of the inside of the pressure switch

a.o. smith motor man. tank and I tie pump

I will get pics for inside the pressure switch, but I have no idea what your last sentence means. Can you decipher for me?

Adam

 

[89MustangGX]

NEW DEVELOPMENT:

I went back and was looking at pics I took from my original thread linked above and I forgot there is a second wire diagram -- it is on a sticker on the side of the compressor. This diagram actually does match how it is wired currently.

What gives?

Why isn't it wired the way I (and I think other people here) think it should be? Is this to save strain on the pressure switch? Isn't this dangerous? At the very least is doesn't make any sense to me.

Help?!?

Adam

 

[GeorgiaHybrid]

Is there a wiring diagram on the motor? Have you tried running it to see if it will build pressure and shutdown?

 

[89MustangGX]

Is there a wiring diagram on the motor? Have you tried running it to see if it will build pressure and shutdown?

No wire diagram on the motor.

Now that I see this sticker with a diagram that matches what I see, I am more confident that the wiring has not been messed with and that it will work.

Questions still remain -- why wire it this way instead of the other? Should I switch it?

It's a Siemen's pressure switch if that makes a difference to anyone.

Adam

 

[89MustangGX]

Some pictures -- pressure switch terminals and wire diagram, and the wiring to the motor.

 

[GeorgiaHybrid]

Is there anyway you can get a clearer picture of the pressure switch wiring?

 

[89MustangGX]

Is there anyway you can get a clearer picture of the pressure switch wiring?

I put a little more light on it.

Thinking about it more -- I am pretty sure this is how it would be wired if it had a magnetic starter on it. It doesn't -- and the specs state it doesn't need it. I wonder if it was originally spec'd with one and it changed in production and they just didn't update this wiring???

So -- should I change the wiring to match the more common switch wiring or is this ok?

Adam

 

[89MustangGX]

In the picture I have all the wiring pulled off, you can see the white wire to the motor looks a little burnt (right), white wire from wall is ok (left) -- those went on the bottom two terminals. Black jumper wire is not installed, it went between the top two terminals. Black wires from wall and motor are wire nutted together (red wire nut). Ground wires not really visible they are on the bottom.

Adam

 

[GeorgiaHybrid]

Have you tried just wiring it back the way it was and see if it runs OK?

 

[89MustangGX]

Have you tried just wiring it back the way it was and see if it runs OK?

No.

I need/want to change the cord anyway, and that's what started this. I am sure that it will work the way it left the factory, just not sure it's the "best" way or the "right" way to do it.

Looking for advice...

Adam

 

[JohnJL]

Did you get this working? Do you have a diagram you could post?

 

[89MustangGX]

Did you get this working? Do you have a diagram you could post?

I wired it as the diagram on the switch indicated, not the diagram on the compressor. Made much more sense to me and seemed like a "safer" method. Have not had any issues, it is working great!

Adam