Help with new(used) compressor

[RRich]

I just bought a used 30gal V-twin Porter Cable 120V. It worked fine at the sellers house but at my garage it doesn't. With the tank pressurized below 20PSI or so it starts and runs perfectly up to 155PSI. When it starts at anything above 30PSI , it starts and makes a few revs but then slows and trips the 20amp breaker if I don't shut it off quickly. I tried other outlets on different breakers with the same result. I could change it to 240V but I'm thinking I should find out what's wrong first. Could it be a capacitor? If so would it be the start or run? How do I know which is which? Why did it work at the sellers house?

 

[sberry]

Is the belt tight? Sounds like maybe the check is leaking back.

 

[mm08822]

Were you able to start the compressor above 30 psi at the seller's location? or did you not try to?

Did the seller have the comp on a 20a ckt or was the cb changed out to something higher?

Does the pressure switch let out a short blast of air once setpoint is reached and motor stops? If not, I would look into the unloader valve on the pressure switch not functioning.

 

[RRich]

Were you able to start the compressor above 30 psi at the seller's location? or did you not try to?

Did the seller have the comp on a 20a ckt or was the cb changed out to something higher?

Does the pressure switch let out a short blast of air once setpoint is reached and motor stops? If not, I would look into the unloader valve on the pressure switch not functioning.

Yes it restarted at about 90psi or so at the sellers house. We ran it then bled it down until it restarted at least twice.
I don't know what amp circuit the seller had.
I will have to check on the unloader valve as I know nothing about this.

 

[RRich]

I just bled it, started it and ran it to shutoff at 155. There was NO noticeable air blast or hiss or anything. What do I do next?

 

[MJO]

Assuming it ran fine at the other guys house and that he wasn't running it on 220 and you didn't damage and/or change anything. I'd use an ammeter to see what it's pulling. It could be the capacitor, could be you have a weak breaker or could be the guy you bought it from had a 30 amp breaker, ask him.

 

[pancho400cid]

Find the motor data plate. What is the running or full load amps (FLA)? A pic of the motor data would be best.

I also wonder if it has an unloader that is not working. When the compressor stops there should be a brief hiss of air. The unloader is often part of the pressure switch. It lets the air between the pump and switch vent out so the motor is not starting with any pressure at all.

The fact that it runs ok from "zero" pressure all the way up, but trips when starting at pressure points to the unloader.

 

[RRich]

FLA 15/7.5
What can I do about the unloader? Is it serviceable?

 

[pancho400cid]

On my compressor it's built into the pressure switch which was about $40 if I recall right. The pressure switch was the issue on mine, not the unloader.

I guess you could take it apart and try cleaning/lubing it but I've never tried.

A motor with 15 running amps on a 20 Amp breaker can have problems with nuisance trips. My 2.0 HP Speedaire was rated right around 15 amps at 120 volts. It would frequently trip my 20 amp breaker. Re-wired it to the 240 VAC config after upgrading to 240 VAC in my gagrage. Problem solved.

 

[walta]

Since it work before you moved if let's think about what could be different.

1 Just because the compressor has 120 volt plug installed is not a guarantee the motor is wired for 120. Some crazy people have been known to wire 120V outlets to provide 240V thru the 120 plug to a motor that is wired for 240V. If someone were to have done this and then plug the cord into a properly wired outlet the symptoms would similar to the ones you described.

2 You said you connected the compressor to a 20 amp circuit. Take a minute check the wire how long is it and what gage. Yes 12 gage is good at 10 feet but not at 200.

3 I have a compressor I lent to a friend the compressor worked great in my shop, but not at his this went back and forth a few times before I replaced the dino oil in the compressor with synthetic oil. It seems his shop was slightly colder and the thicker oil would sometimes not allow the motor to get started.

Please post a few photos. Most should hiss when they shut off.


Walta

 

[Citation]

Could be just bad luck timing. Perhaps the starter cap on the motor. With a low load the motor can start with no issues. Once it has to start into a higher pressure tank the starter cap is an issue.

While it could be bad luck the seller might have known and made sure to fill from empty. If it's a cap it's not an expensive fix.

 

[fitter30]

Unloader valve opens when compressor is off and removes any trapped air on top
of the piston. Some valves that are mounted on the side of the switch can be removed and checked out make sure tank is empty.
Check the motor wiring to see what voltage it's wired for.

 

[RRich]

Thanks to everyone for the great suggestions! I have no way to check the actual current draw. I checked and the motor IS correctly wired for 120V. The unloader is a plastic angle fitting under the pressure switch connected to a plastic line running to the compressor discharge fitting. After the motor shuts down at 155psi, there is no discharge of air at the valve. When I remove the plastic line(quick release) there is a very noticeable air discharge. I assume this means the unloader is not working. Tomorrow I'll see if I can remove it.

 

[walta]

Plastic line?????


The air coming out of the compressors head is very warm, could be 200° maybe. Most plastics cannot take that much heat.

Look at the unloader generally a lever pushes on a valve to let the air escape.
A new pressure switch with unloader is surprisingly inexpensive $15 shipped

https://www.amazon.com/gp/product/B00QI0WGFS/?tag=atomicindus08-20


Walta

 

[RRich]

Plastic line?????


The air coming out of the compressors head is very warm, could be 200° maybe. Most plastics cannot take that much heat.

Look at the unloader generally a lever pushes on a valve to let the air escape.
A new pressure switch with unloader is surprisingly inexpensive $15 shipped

https://www.amazon.com/gp/product/B00QI0WGFS/?tag=atomicindus08-20


Walta

Lots of compressors use a plastic line to the unloader. I found a UTube of my exact model and the guy measured the outlet air temp at the cyl head at 120 max.
Unfortunately the switch you linked is not the correct one. The correct one is $30xx. I can get just the unloader valve on ebay for $12.60.

 

[RRich]

I installed the replacement unloader valve and it didn't solve the problem. I guess I need to learn about capacitors.

 

[mm08822]

I installed the replacement unloader valve and it didn't solve the problem. I guess I need to learn about capacitors.

Does the new unloader valve you installed now provide a blast of air upon shutoff?

 

[The Cobbler]

who knows what sort of amp breaker the seller had, could have been 30 amp just to cover up an issue to sell it.
so before you go any farther, I would run the compressor up to pressure.
undo the unloader line and see what happens .
leave it open, drain down pressure, let compressor kick on . see if it starts .

I would not think it's the check valve leaking back, if the unloader is working it would just bleed off the air to atmosphere, not put pressure on the pump
I had a craftsman compressor that would 50% of the time not start at tank pressure without blowing the breaker.
everything checked out fine. even with a 20 amp breaker it would often blow. I added a cold start unloader valve into the system & it performed flawlessly . I will dig up the thread if you want

 

[ddawg16]

Grab a voltmeter and measure the voltage at the outlet when you turn it on. Plug the leads into the other outlet. When you turn it on, you will see the voltage going to the plug for the compressor. It should be at least 105 or higher. If lower, it's possible you have a problem you don't know about.

If it's above 105, then measure the voltage at the motor.

You might have a wiring issue you didn't know about.

 

[The Cobbler]

I looked on ebay for 30gal V-twin Porter Cable compressor . It runs at 12 amp, PC recommends a 25 amp breaker on them .

in that case I would be tempted to run it on 15amp 240

 

[ClappedOutBport]

My compressor will blow one breaker in my house consistently and rapidly, but another circuit handles it fine. Perhaps just try a different circuit.

 

[sberry]

Put 50 ft of 14 cord on see if trips. 25/16 works for a test too.

 

[RRich]

Thanks again for all the suggestions. The original unloader valve was not working, the new one is. I tried many outlets on different breakers when trying to solve this before I replaced the unloader valve. It didn't matter which outlet I tried, they all flipped a breaker. After replacing the unloader valve, I tried it out on the closest outlet and it acted the same as it did originally. Today I measured the voltage at the outlet as suggested and saw it dropped to 76 at startup (from 122). I moved to another outlet close to the breaker box and tried it. 88 at startup and to my great delight the compressor quickly got up to speed and the voltage rose to a steady 112. I've started and stopped it many times now and it's working perfectly. So I really had two problems with exactly the same symptom. This has been a good learning experience.
THANKS AGAIN to everyone who responded!

 

[ddawg16]

Thanks again for all the suggestions. The original unloader valve was not working, the new one is. I tried many outlets on different breakers when trying to solve this before I replaced the unloader valve. It didn't matter which outlet I tried, they all flipped a breaker. After replacing the unloader valve, I tried it out on the closest outlet and it acted the same as it did originally. Today I measured the voltage at the outlet as suggested and saw it dropped to 76 at startup (from 122). I moved to another outlet close to the breaker box and tried it. 88 at startup and to my great delight the compressor quickly got up to speed and the voltage rose to a steady 112. I've started and stopped it many times now and it's working perfectly. So I really had two problems with exactly the same symptom. This has been a good learning experience.
THANKS AGAIN to everyone who responded!

Time to pull all your outlets and check the wiring. That is WAY too much of a voltage drop. I'm betting the daisy chain is using the outlet as the connection point.

Look up 'pig tail'. That is the best way to wire them.

 

[dave*99]

I had startup issues about 30 years ago with a 1 HP craftsman 12 gal. compressor. Solved them all when I put in on a dedicated 120V 20A circuit.

Many years later I gave it to my BIL.

And the next day we solved all his startup problems by putting in on a dedicated 120V 20A circuit.

 

[sberry]

It would be I nteresting to know the low. The current is 12 run, start on an older cheap comp is probably 75, or could be, give it 25 ft of wire how low does the start voltage normally go?
But if a guy has start problems, has the spaces and doesn't mind the conversion 240 is great for starts.
Lots of them run good new. They get older, used, sometimes causes some extra start draw.

 

[sberry]

I got 1 hp on a table saw and 1 on the paint fan, use them on 20/120 and they are fine. I have a common 14 inch heavy chop saw and it will trip a 20 especially with slight heavier blade. My helper ran another set of wires, ran 10 which we had but would have used 12 if I did it. Got a 30 on it.
Lights on another 20 circuit.

 

[ddawg16]

Fun story...........sort of

I have a Sears radial arm saw.

Back when the wife (fiance) and I were in an apartment that included half a 2 car garage, I had a small workshop...which included my saw.

I was having startup issues. I couldn't get the saw to get up to speed.

So I was messing with it.

First test.....remove the blade and see if the motor gets up to speed. It does.

Second test...put blade back on.....

Well.........I didn't tighten the nut for the blade.
While watching the blade speed...I saw the nut fall off......and shortly behind it was the blade....

It shot across the room....up the wall...across the ceiling.....then coming to rest on a box.
I still have the sanding block that was almost cut in half by the blade.

I am so lucky....that incident could have gotten ugly fast.

Moral of the story.....don't use a cheap *** extension cord. Mine was a 75' 16AWG extension cord.

I replaced it with a 12AWG cord. Saw worked fine after that.

 

[SGKent]

Do you have a 1500 watt hair drier in the house. Plug it into the same socket that the compressor was in when you had 76V and see what the voltage is. It could be that the line in to the house is old and needs replacement. It may be a Godsend you discovered it now before you lost any major appliances. I've lived in 3 homes over my 70 years where the power company had to come out and replace the lines coming into the house because of excessive voltage drop. My next door neighbor here had it happen with one of his underground lines. I even had it happen in this house on one leg and after arguing with the power co for a year about it being their intermittent problem, one morning the power transformer down the street burned up on that leg. When they replaced the transformer the problem went away.

 

[RRich]

Do you have a 1500 watt hair drier in the house. Plug it into the same socket that the compressor was in when you had 76V and see what the voltage is. It could be that the line in to the house is old and needs replacement. It may be a Godsend you discovered it now before you lost any major appliances. I've lived in 3 homes over my 70 years where the power company had to come out and replace the lines coming into the house because of excessive voltage drop. My next door neighbor here had it happen with one of his underground lines. I even had it happen in this house on one leg and after arguing with the power co for a year about it being their intermittent problem, one morning the power transformer down the street burned up on that leg. When they replaced the transformer the problem went away.

Interesting idea. Sometime I'll get out my heat gun and meter and check the whole house. I guess if the pool pump, water heater, and well pump happen to be on at the same time(very possible), there would be a drop off for the rest of the house. The house was built in 2001.

 

[ddawg16]

I use an iron. But an hair dryer works just as well....it helps to have a clamp on amp probe to confirm the draw. A clothes iron is typically going to be a bit more consistent

 

[SGKent]

I would not wait on testing. If you have problems with the main line in on either leg you will see a big voltage drop. If the compressor can pull the system down to 76V there is a fire hazard somewhere or a shorted winding in the new used compressor motor.

 

[nsula_country]

Backstabbed receptacles?

Voltage drop?

CT

 

[RRich]

Although the compressor has been working, it sounded like it's struggling to reach 155psi. Today I installed a dedicated 240 outlet and rewired the motor. What a difference! Sounds like it's running at double speed effortlessly. I guess the CFM rating would have to be much better now. Soon I'll time it from empty to shutoff. I know it took just over 7 min on 120V.