I have a 10 year old Craftsman air compressor (919.153131) that won't
shut off. I had a problem with it not starting with pressure in the
tank and I replaced the check valve and fixed the problem.
It ran good for a short period of time. Now it will not shut off when
it reaches the upper pressure limit. The relief valve opens and
drains off some pressure but the compressor keeps running.
Does anyone have any suggestions as to the problem?
I did a check on the sears web site for you compressor, the part no.
you need is No.43, it cost $53.99 and is called the pressure switch...
it is suppose to turn the compressor off electricallly as the pressure
goes up to its limints(in your case probably 150 lbs. of pressure)...
it might just be the contacts sticking on your pressure switch?? you can
take off the sheet metal case off the switch and see what happpens when
you get the top pressure like 150 lbs???? make sure the little metal arm
that is on side of the pressure switch box is not bendt into the on
position as this might be what is stopping it from turning the
electricity off???? hope this helps.
Having just rebuilt my compressor (see www.228mill.com/tinker.htm ) I
can offer the following suggestion:
Your compressor should have a pressure switch on it (looks like a
black box) where the the power wire and the motor wire run to. This is
what controls the start & stop cycle of the compressor. It's also
connected to the tank to sense the pressure and should also have a
connection for a little hose that relieves the piston pressure once
the motor shuts off.
It's a mechanical device and may just be "gunked up" based on your
description of the *two* pressure related problems you described. Once
your tank is completely depressureized you can try and "futz" around
with it (unplug you machine please - that's real live 'lectricity
running through them wires) and try and clean/oil it.
There should be a bulky set-screw at the top that controls the on-off
pressure. You can try and turn it back and forth to loosen any
stickyness - make sure you set it back to the original position.
It could also be that the electrical contacts are fryed and the switch
is actually working - It's hard to hear when the machine is running,
but there should be a definite "click" when the tank reaches the
If you really have to, you can take it off and disconnect everything
but this is a real PITA. you will have to reseal and reconnect
Failing that, you will need to replace it. a big new one (5HP 220v)
cost me about $65 Canadian (40US)
Let me know if you need more help
firstname.lastname@example.org (Zig) wrote in message
Although I agree with the sentiment of this statement, PLEASE don't do
that. Sandpaper leaves particles imbedded in the contacts which cause
arcing and subsequent failure of the contacts - especially on high
current applications like air compressor motors.
Instead, use a burnisher or riffling file to clean the contacts.
Anything that doesn't shed abrasives or other particles when used, but
removes debris and restores contact surfaces. Take it easy, because
many better relay and switch contacts are silver or gold plated.
Don't want to remove any more of the coating than absolutely
I guess many folks never worked on contacts. During my working days
burnished zillion contacts. Well worked in phone switching plant once
in the days of step-by-step, strogger stuffs. Any old timers remember
What's with the "old timer" !
I started working for the phone company (BT) just as the last of the
Strowgers were disappearing. I still remember contact burninshing,
the most tedious job in an exchange.
Now I restore Japanese swords. A usable material for the hilt wrapping
on a WW2 military mounting is the flat cotton tubular tape used as the
polishing medium for bank cleaning on a Strowger. Instead of slipping
a length over a polishing hook, dye it green or brown and use it
Die Gotterspammerung - Junkmail of the Gods
i have used very fine emery cloth on power contacts. you can use
just typing paper and a solvent like 90% Isopropal alcohol, force
the contacts closed on paper and pull it thru. repeat until the
paper remains white. --Loren
While sanding and burnishing might work for a while, once the contacts
are worn, they'll tend to stick again. I've noticed that the quality
of contacts on newer compressors has become worse than on old ones, or
maybe I'm just getting cynical.
A solution that fixes the problem once and for all, and for less than
the part cost of a new pressure switch is to use the old pressure
switch (after you've pried the welded contacts appart) to drive a
transformer/filter to drive the LED of a solid state relay. The relay
drives the motor and will never arc; it should last forever. I've
done that on one setup and it has worked great for years (5hp 220v
compressor). I now have another compressor's switch going bad and ran
across a surplus 240v 40A Furnas DPST contactor for $6, so I'll use
that in place of the solid state relay. The contactor is a simpler
(no transformer/filter and heatsink on the relay needed) and cheaper
solution and this compressor doesn't get nearly the use of the other
one. It won't last forever, but the 40A contacts should be good for
far longer than a replacement pressure switch.
Another approach, after burnishing the contacts is to apply a
de-oxidizing / anti-arc coating. Caig Laboratories makes an entire
Search the site for the application guide.
I can vouch for it's effectiveness. I used to maintain an old 16-track
MCI tape deck. Each channel had 4 relays in addition to the relays in
the transport controls. Once I started using Cramolin (now called
ProGold, I think) I seldom had to do anything to that machine.
On 5 Nov 2003 12:26:24 -0800, email@example.com wrote:
this is one good idea. your testing seems to inidcate one old idea
may be untrue, that running signals thru contacts will not work.
assuming you can get the contacts free, it s/b easier to install
an scr than a replacement pressure sw assy. thanks! --Loren
Back in the day of engines with contact points ignition seems most
people knew not to use an abrasive coated paper to clean them.
Something that should be noted, on a set of coated contacts, once the
coating has been breached performance drops, sometimes drastically. A
set of contacts may last 10 years with the coating intact, may last 10
cycles once the base metals been exposed (I know it's an extreme example).
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