Air compressor runs for a few senconds

[Jgsloan7]

Hi all new to the forum!
I have a kobalt 30 gallon air compressor. Its 2 stage 1.8 HP, 120V. I bought it used 6 months ago and no problems until now. I turn it on and it winds up then it just stops spinning and the motor keeps trying to turn. Ive let all the air out and it does the same. I took the belt off and the motor spins fine. I can turn it by hand no problem. I check the start capacitors and the meter says theyre good. It also has a weird sort of burning smell but I cant tell where its coming from. The oil level is fine. Im thinking of trying an oil change with synthetic, maybe the cold weather is messing with it?

 

[Tha fios agaibh]

motor spinds fine. I can turn it by hand no problem.

Welcome. Can you also turn the compressor side by hand, or perhaps with a pair of pliers?
I think it's more likely to be a mechanical problem than an electrical problem.
Perhaps a bearing or the piston is siezing up once it warms up?

 

[Jgsloan7]

Welcome. Can you also turn the compressor side by hand, or perhaps with a pair of pliers?
I think it's more likely to be a mechanical problem than an electrical problem.
Perhaps a bearing or the piston is siezing up once it warms up?

Once it warms up it runs fine! It takes a while of switching on and off to get it going. Yes I can turn it by hand with ease! Any other ideas?

 

[Bluejets]

Switching on and off is not a good way to go.

Noticed motor is a dual voltage motor....connections haven't been altered in any way..?

Usually start problems are related to faulty capacitors ..........
or the unloader valve not operating correctly if at all........ I'd go for the latter
Not running it on a long extension lead by any chance....???

Also associated with the unloader (incorporated in the pressure switch) there is a rubber valve , spring and ball assy in the top of the tank.

 

[Tha fios agaibh]

If its really cold it could be the problem. (oil getting thick in cold temp)
You could try a heater near the crankcase to warm the oil before hand to see if that's your problem.
Or, try pulling the ring on the unloader valve when starting it until the oil warms up after a few minutes.

 

[Jgsloan7]

Switching on and off is not a good way to go.

Noticed motor is a dual voltage motor....connections haven't been altered in any way..?

Usually start problems are related to faulty capacitors ..........
or the unloader valve not operating correctly if at all........ I'd go for the latter
Not running it on a long extension lead by any chance....???

Also associated with the unloader (incorporated in the pressure switch) there is a rubber valve , spring and ball assy in the top of the tank.

Well I didnt have much of a choice on the on amd off. i had to get my truck back together in the morning before work lol. I had all4 tires off. The voltage has always been 120 as far as I know, so that has not been messed with.

I tested the capacitors and they were good, but I guess it wouldnt hurt to replace them. I can go ahead and put in a new unloader valve as well tonight. Ill see if that fixes it. Ill also check out the assembly on top of the tank. Thank you!

 

[Jgsloan7]

If its really cold it could be the problem. (oil getting thick in cold temp)
You could try a heater near the crankcase to warm the oil before hand to see if that's your problem.
Or, try pulling the ring on the unloader valve when starting it until the oil warms up after a few minutes.

Im not sure if the oil is the problem anymore . Yesterday it got up to 48 degrees farenheit. So there should be no problem with any oil at that temperature. I'll definitely try pulling the ring. Thank yall for all of the help!

 

[Bluejets]

Well I didnt have much of a choice on the on amd off. i had to get my truck back together in the morning before work lol. I had all4 tires off. The voltage has always been 120 as far as I know, so that has not been messed with.

I tested the capacitors and they were good, but I guess it wouldnt hurt to replace them. I can go ahead and put in a new unloader valve as well tonight. Ill see if that fixes it. Ill also check out the assembly on top of the tank. Thank you!

How were the caps tested..??
"AS far as you know" is not a method for confirming the correct motor connections.
Might be a good move for you to Google just how an unloader valve works as there are a few parts to it not "just a valve".

 

[Jgsloan7]

How were the caps tested..??
"AS far as you know" is not a method for confirming the correct motor connections.
Might be a good move for you to Google just how an unloader valve works as there are a few parts to it not "just a valve".

Sorry I was at a redlight trying to type and answer you. I did understand after re-reading your post. I have been out of town for work. Im back now.

So the unloader valve is built into the switch, so I'm not sure how to see if its working. What should i use to clean the switch and valve? Wd40? Canned air?

the check valve in the tank is stuck, is it ok to use pb blaster or will it leak into the tank and cause problems?

Thank you for all your help i really appreciate it.

 

[Jgsloan7]

How were the caps tested..??
"AS far as you know" is not a method for confirming the correct motor connections.
Might be a good move for you to Google just how an unloader valve works as there are a few parts to it not "just a valve".

I tested the caps with a fluke 87 multi meter. I went ahead and replaced the start capacitor, but i dont want to crank it up without and oild change, and I am going to change the check valve in the tank too while I'm at it

 

[Bluejets]

I looked for Fluke 87 multimeter and although there may well be variants, I did not see any with capacitor testing facility.
Best to show a photo of your test gear at the time.

The tank valve can be a ball and spring or a spring loaded rubber disc.
It operates when compressor feeds pressure higher than the tank, so on every stroke the valve is pulsing open and closed.
Purely mechanical and any damage would be obvious.
It is accessed through the large nut on the T body screwed into the tank.

The relief section is part of the pressure switch and there are no serviceable parts within.
A small diameter pipe leads from the previous T section up to (usually) the bottom of the switch.
Under normal operation, as the pressure in the tank bleeds down and compressor not running, this valve is open, allowing only atmospheric pressure to the heads.
When the pressure switch kicks in, it closes this valve and allows head pressure to drive through the T section.
When shut-off pressure is reached, the pressure switch again opens this small valve and due to the T section valve, only the head pressure is released.
This is obvious by a one or two second hiss as the unloader operates at shut down.

The whole idea is to relieve the head pressure during the initial start period of maybe 1 or 2 seconds.
If the unloader in the pressure switch is defective, it either will not hiss at shutdown or it hisses continuously.
If the T body valve is defective , the unloader valve will hiss continuously.

If none of the above , then motor start winding may be damaged.
If running on long extension leads, motor can also be damaged and might not be obvious.
For some people, as long as it runs, then all ok on the far side of the moon.
What will happen in this instance is the start winding can re-energise and cook itself.

 

[DJL33B]

This sounds like the problem I have (had) with my compressor. According to 'Ugly's Electrical References', a 1.8 HP motor operating at 120 VAC will draw between 20 and 24 amps, running. This would indicate the need for a 30 Amp circuit, with #10 wire. This would eliminate the typical plug-in use. If the motor tries to start with the tank partially pressurized, the load increases.
This is when the unloader valve should help. My compressor had the problem in both hot & cold weather. I fixed the problem with a heavier circuit.

 

[Tha fios agaibh]

a 1.8 HP motor operating at 120 VAC will draw between 20 and 24 amps, running.

This 1.8 HP is most likely a "peak HP" rating thats commonly used for marketing to make product sound better. The actual HP rating is probably 1/2HP or less.

 

[DJL33B]

This 1.8 HP is most likely a "peak HP" rating thats commonly used for marketing to make product sound better. The actual HP rating is probably 1/2HP or less.

My point is that the same symptoms were cured by installing a heavier line.