Air compressor help

[JHPIII]

Ok I have a central pneumatic air compressor(I know it’s a pos but it is good enough for what I’m using it for)
It starts up and runs fine up to 125 psi but when it runs down to the 90psi during in pressure the compressor struggles to start. If I run it down to 25 psi or lower it will start fine. Also if I push down on cold start valve it will start. Ive replaced cold start valve. I’ve replaced pressure switch with unloaded valve already. Any ideas?

 

[DieselTech]

Motor start ballast/capacitor.

 

[DieselTech]

Post a couple pics of the motor.

 

[kenh]

When the compressor shuts off, can you hear the unloader valve release air? If not, maybe it is just misadjusted??
Funny thing, The pressure switch/unloader valve from my original sears air compressor from 50 years ago is the only functioning part left. It's installed on my frankenpressor.

Ken

 

[JHPIII]

Couldn’t figure out how to upload the video hopefully these pics help. I really think it’s a design flaw in where they located this cold start valve right on top of the head.

 

[PlayingWithTBI]

As mentioned above, it could be your starting Capacitor and/or the relief valve.

Show us a picture of the motor.

Does it hiss when it shuts off when it reaches pressure?

 

[RichLo]

That valve doesnt effect the electric motor, once it tries to spin the valve did its job.

Are you running it with an extension cord? if so, what size and length? Have you unplugged it recently to check the conditions of both the compressor prongs and the outlet? Whats the stats on the motor? Take a pic of the info sticker on the motor.

I worked with my foreman electrician at work to help setup my 10hp massive compressor at home. The startup amps are insane on electric motors and most homeowner grade hardware is not rated for that load. They may be fine for years but eventually they will fail.

Also, just like truck help... what is your exact make/model/year purchased compressor?

 

[PlayingWithTBI]

The startup amps are insane on electric motors and most homeowner grade hardware is not rated for that load.

Yeah, up to 7 times their rated running Amperage (FLA).

I went through this a few years ago. Mine has 2 Capacitors, a start and a run Cap. Some motors have a combo Start/Run Cap, and some have a start only. These are single phase motors, a 3 phase motor doesn't need one.

Anyway, I bought a cheap digital gauge for Capacitor's MFD reading. I found one of them bad. I also replaced the starter on it since the old one's contacts were getting worn and, sometimes they'd stick causing the compressor to run continuously while blowing off relief valve.

This is what we're asking for.

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And this

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Here's my El Cheapo tester. This Cap is good.

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Old Starter (Furnas are junk)

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New starter going in.

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Anyway, this is why we're all asking for more details.

 

[JHPIII]

Sorry could not take any pics got called into work today the pics I posted were of a video I took of the issue yesterday.
I will try and get some tomorrow. It is a central pneumatic 2.5 hp 21 gal upright not sure of model number I will try and get that tomorrow too.
But just so we are clear. When I turn on the compressor ot starts and runs normally. It fills to 125 psi and gives the little hiss at the end. When I let air out of it it goes down to the cut in pressure at 90 psi and tries to start but can’t. But if while it is trying to start I hold the little valve stem in on that cold start valve it will take off and run fine right back to 125psi.
I have also while it is full at 125psi cracked the line to the unloaded valve and there is no hiss. I have also removed the cold start valve and there is no hiss. So I believe the unloaded valve is doing its job as there seems not to be any pressure on the compressor side of the check valve.
Seems to me if it was a start capacitor or run capacitor. Holding that cold start valve shouldn’t really do anything?
I also noticed on the later models the cold start valve was relocated into a t in the line going to the tank instead of right on top of the head.
Anyways thanks for all the responses I’ll try and get the info and pics posted tomorrow when I can get home.

 

[at7615]

Sorry could not take any pics got called into work today the pics I posted were of a video I took of the issue yesterday.
I will try and get some tomorrow. It is a central pneumatic 2.5 hp 21 gal upright not sure of model number I will try and get that tomorrow too.
But just so we are clear. When I turn on the compressor ot starts and runs normally. It fills to 125 psi and gives the little hiss at the end. When I let air out of it it goes down to the cut in pressure at 90 psi and tries to start but can’t. But if while it is trying to start I hold the little valve stem in on that cold start valve it will take off and run fine right back to 125psi.
I have also while it is full at 125psi cracked the line to the unloaded valve and there is no hiss. I have also removed the cold start valve and there is no hiss. So I believe the unloaded valve is doing its job as there seems not to be any pressure on the compressor side of the check valve.
Seems to me if it was a start capacitor or run capacitor. Holding that cold start valve shouldn’t really do anything?
I also noticed on the later models the cold start valve was relocated into a t in the line going to the tank instead of right on top of the head.
Anyways thanks for all the responses I’ll try and get the info and pics posted tomorrow when I can get home.

Voltage drop?

 

[kenh]

The pressure relief/cold start valve should be part of the pressure switch. When the switch opens stopping the motor it should trigger the pressure relief. That is why it was asked if it hisses when the motor stops. In Playing with TBI post the pressure relief is to the left of the big spring in his pressure switch. It has a 1/4" line running to it. In any case, I would question HF about this. It may net you a new compressor or at least repair parts. If not a proper pressure switch with a built in relief will solve the problem.

Ken

 

[DieselTech]

Start/run Capacitor bad.

 

[RichLo]

Please also take a pic of the valve that you are holding down that allows it to startup at 90psi.

I got my compressor on auction for $100 and spent over $500 in industrial parts to get it to run how I wanted. Its a Beast, 35cfm@90psi compressor head and I have it setup to run to 170psi and turn back on at 135psi. It gets from 0-170 in less than a minute... I've learned that it takes A LOT to startup that compressor at 135psi, lol.

 

[JHPIII]

Thanks for all the responses guys. Like I said I will hopefully get out of here at a descent time and try to get some pics.
This is the cold start valve that I replaced on top of the head

https://a.co/d/06lzVb06

This is the pressure switch with unloader that I replaced
https://www.walmart.com/ip/Lefoo-95...itch-1-4-Female-NPT-4-Port-LF10-L4H/823103297

I really do not think that either were bad.

I found a couple videos online where people with similar problems added a tee on top of the head and installed two cold start valves. I might try that although I think the real fix would be to put a t inline off the side of the head to feed the air tank and move the cold start valve to there.

Away about 1:45 in this video kid shows where the cold start valve is located on the newer compressors instead of on top of the head.

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Anyways thanks for the help will try and get some more info for you all when I finally get home.
And it’s a cheap compressor I bought for like 100 bucks like years ago but it’s good enough for the small projects I use it for.

 

[at7615]

Thanks for all the responses guys. Like I said I will hopefully get out of here at a descent time and try to get some pics.
This is the cold start valve that I replaced on top of the head

https://a.co/d/06lzVb06

This is the pressure switch with unloader that I replaced
https://www.walmart.com/ip/Lefoo-95...itch-1-4-Female-NPT-4-Port-LF10-L4H/823103297

I really do not think that either were bad.

I found a couple videos online where people with similar problems added a tee on top of the head and installed two cold start valves. I might try that although I think the real fix would be to put a t inline off the side of the head to feed the air tank and move the cold start valve to there.

Away about 1:45 in this video kid shows where the cold start valve is located on the newer compressors instead of on top of the head.

xc_hide_links_from_guests_guests_error_hide_media

Anyways thanks for the help will try and get some more info for you all when I finally get home.
And it’s a cheap compressor I bought for like 100 bucks like years ago but it’s good enough for the small projects I use it for.

I got one of these at the airport, it must have a 12 gauge wire 20 Amp circuit or it will hang up just like yours.

 

[JHPIII]

I got one of these at the airport, it must have a 12 gauge wire 20 Amp circuit or it will hang up just like yours.

Hey sorry for the late response work was s##t this week finally have a minute off and figured I’d give this a try before throwing any more parts at it and you sir are the winner. Switched to 12ga extension cord and compressor operates perfectly. Should have asked here first could’ve saved $30 bucks but I guess I got some spare parts now lol
Thanks again all; the responsiveness and help on this site is amazing.

 

[RichLo]

lol, or just read my first post in this thread and responded accordingly.

 

[at7615]

Hey sorry for the late response work was s##t this week finally have a minute off and figured I’d give this a try before throwing any more parts at it and you sir are the winner. Switched to 12ga extension cord and compressor operates perfectly. Should have asked here first could’ve saved $30 bucks but I guess I got some spare parts now lol
Thanks again all; the responsiveness and help on this site is amazing.

Thanks for the feedback, it helps others in similar situations.

 

[JHPIII]

lol, or just read my first post in this thread and responded accordingly.

Yeah sorry I knew I saw someone else say extension cord but old eyes tired from work and reading on my phone couldn’t find it. It anyways thanks all it was nice to get home from work and just switch to my heavy cord and have it work. Hopefully rain takes a break today and I can shoot some paint.