I have a problem with my 4 hp cambell hausfeld oiless direct drive air
compressor. When empty it will start and work fine but if there is 50 + psi
in the tank the motor tries to start and the thermal overload keeps tripping
out. I checked the check valve and it is clean and moves freely, also the
unloader valve is clean and seems to work fine. Could the problem be in the
motor, or its capacitors? Any other ideas? Thanks

Sounds like the pressure switch to me. You already ruled out the motor and
capacitors yourself by saying that it works fine until there is 50 psi. That
tells me the pressure switch is faulty

Searcher1

"habbi" wrote in message
...
I have a problem with my 4 hp cambell hausfeld oiless direct drive air
compressor. When empty it will start and work fine but if there is 50 +
psi
in the tank the motor tries to start and the thermal overload keeps
tripping
out. I checked the check valve and it is clean and moves freely, also the
unloader valve is clean and seems to work fine. Could the problem be in
the
motor, or its capacitors? Any other ideas? Thanks

On Sat, 27 Nov 2004 01:06:22 +0000, habbi wrote:

I have a problem with my 4 hp cambell hausfeld oiless direct drive air
compressor. When empty it will start and work fine but if there is 50 +
psi in the tank the motor tries to start and the thermal overload keeps
tripping out. I checked the check valve and it is clean and moves freely,
also the unloader valve is clean and seems to work fine. Could the problem
be in the motor, or its capacitors? Any other ideas? Thanks

That sounds like the compressor isn't unloaded. Either because the
unloader isn't functioning or because tank pressure is leaking back into
the compressor. You should be able to find out what's happening by
cracking the output connection right after the unit cycles off at
pressure. Evidence of high pressure release would indicate that the
unloader isn't working. Cracking the output connection after the unit has
sits a while with the airtank above 50psi will tell you if there's leak
back.

It is also possible that there's a motor problem. Swapping out the start
capacitor would be a pretty cheap diagnostic.

--
The instructions said to use Windows 98 or better, so I installed RedHat.

What Jim said. Either the unlaoder or the start cap. Try the unloader
first.

Jim Levie wrote:

On Sat, 27 Nov 2004 01:06:22 +0000, habbi wrote:


I have a problem with my 4 hp cambell hausfeld oiless direct drive air
compressor. When empty it will start and work fine but if there is 50 +
psi in the tank the motor tries to start and the thermal overload keeps
tripping out. I checked the check valve and it is clean and moves freely,
also the unloader valve is clean and seems to work fine. Could the problem
be in the motor, or its capacitors? Any other ideas? Thanks


That sounds like the compressor isn't unloaded. Either because the
unloader isn't functioning or because tank pressure is leaking back into
the compressor. You should be able to find out what's happening by
cracking the output connection right after the unit cycles off at
pressure. Evidence of high pressure release would indicate that the
unloader isn't working. Cracking the output connection after the unit has
sits a while with the airtank above 50psi will tell you if there's leak
back.

It is also possible that there's a motor problem. Swapping out the start
capacitor would be a pretty cheap diagnostic.

After ruling out any and all pressure, check valve etc... problems I took
off the end of the motor and fiddles with the thing in side that switches
from start windings to the run windings. After I put it back together it
seemed to work better. In hindsight it did seem to start slow even when the
tank was empty but now it is like it used to be, almost instant start up at
any pressure. What could have been wrong. Could it have been trying to start
on the run windings? Can the capacitors get weak or do they just die?
"RoyJ" wrote in message
ink.net...
What Jim said. Either the unlaoder or the start cap. Try the unloader
first.

Jim Levie wrote:

On Sat, 27 Nov 2004 01:06:22 +0000, habbi wrote:


I have a problem with my 4 hp cambell hausfeld oiless direct drive air
compressor. When empty it will start and work fine but if there is 50 +
psi in the tank the motor tries to start and the thermal overload keeps
tripping out. I checked the check valve and it is clean and moves
freely,
also the unloader valve is clean and seems to work fine. Could the
problem
be in the motor, or its capacitors? Any other ideas? Thanks


That sounds like the compressor isn't unloaded. Either because the
unloader isn't functioning or because tank pressure is leaking back into
the compressor. You should be able to find out what's happening by
cracking the output connection right after the unit cycles off at
pressure. Evidence of high pressure release would indicate that the
unloader isn't working. Cracking the output connection after the unit
has
sits a while with the airtank above 50psi will tell you if there's leak
back.

It is also possible that there's a motor problem. Swapping out the start
capacitor would be a pretty cheap diagnostic.

On Sat, 27 Nov 2004 21:35:47 GMT, "habbi"
wrote:

After ruling out any and all pressure, check valve etc... problems I took
off the end of the motor and fiddles with the thing in side that switches
from start windings to the run windings. After I put it back together it
seemed to work better. In hindsight it did seem to start slow even when the
tank was empty but now it is like it used to be, almost instant start up at
any pressure. What could have been wrong. Could it have been trying to start
on the run windings? Can the capacitors get weak or do they just die?

If the centrifugal start switch was stuck in the Run position, it
would never cut in the start windings when it spun down - do you now
hear a distinct "click" as the motor starts up, and another as it
coasts to a stop?

It might have been able to start the motor on the Run windings alone
with no air pressure in the tank, but with any backpressure at all
past the check valve it wouldn't go. It wouldn't reach speed before
the tubing between the compressor and the check valve pressurized and
stalled the motor.

I had to cheat to make an airbrush system out of a 1/3 HP diaphragm
compressor that could not start reliably against head pressure - used
a 10-second cam-switch motor sequencer, a self-latching (drop-out)
motor relay and a solenoid valve for the unloader. Leaving the
unloader valve open for 5 seconds after motor start (until the motor
came up to speed) allowed it to work every time against a tank and
check valve.
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Go here http://www.chpower.com/ ... look at item 32 looks like a relief
valve or unloader , then start pump while pulling ring on relief valve ...
if pump starts you got it , get new valve... if not then I would contact
them.
If you keep up what your doing and smell something like burnt paint... it's
the motor.
4 hp sounds like a BIG motor for 220 single phase ... what's that thing draw
?

"Bruce L. Bergman" wrote in message
...
On Sat, 27 Nov 2004 21:35:47 GMT, "habbi"
wrote:

After ruling out any and all pressure, check valve etc... problems I took
off the end of the motor and fiddles with the thing in side that switches
from start windings to the run windings. After I put it back together it
seemed to work better. In hindsight it did seem to start slow even when
the
tank was empty but now it is like it used to be, almost instant start up
at
any pressure. What could have been wrong. Could it have been trying to
start
on the run windings? Can the capacitors get weak or do they just die?

If the centrifugal start switch was stuck in the Run position, it
would never cut in the start windings when it spun down - do you now
hear a distinct "click" as the motor starts up, and another as it
coasts to a stop?

It might have been able to start the motor on the Run windings alone
with no air pressure in the tank, but with any backpressure at all
past the check valve it wouldn't go. It wouldn't reach speed before
the tubing between the compressor and the check valve pressurized and
stalled the motor.

I had to cheat to make an airbrush system out of a 1/3 HP diaphragm
compressor that could not start reliably against head pressure - used
a 10-second cam-switch motor sequencer, a self-latching (drop-out)
motor relay and a solenoid valve for the unloader. Leaving the
unloader valve open for 5 seconds after motor start (until the motor
came up to speed) allowed it to work every time against a tank and
check valve.
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

habbi wrote:

After ruling out any and all pressure, check valve etc... problems I took
off the end of the motor and fiddles with the thing in side that switches
from start windings to the run windings. After I put it back together it
seemed to work better. In hindsight it did seem to start slow even when the
tank was empty but now it is like it used to be, almost instant start up at
any pressure. What could have been wrong. Could it have been trying to start
on the run windings? Can the capacitors get weak or do they just die?

I have a similar situation: the compressor has a difficult time starting
and if it's cold, it won't start at all (labors slowly along until the
breaker trips). The only way that it starts instantly is if the outlet
from the compressor head is disconnected. I *definitely* ruled out the
unloader and the check valve. BTW - the check valve cannot be the
problem if the unloader is working: the unloader drains the pressure
between the compressor and the check valve. A bad check valve would
just bleed down the tank through the unloader. The capacitors are ok on
a go/no-go basis (not short or open).

When I saw "habbi's" post I checked my centrifugal switch. It was
pitted, so I cleaned it. When I tried it, I noticed a lot of arcing
during start (it still didn't start right up). It was "hunting": at
stop the switch is closed and it gets *almost* to speed and the switch
opens. Which causes it to slow and re-close the switch. This repeats.
When it has warmed up it doesn't do it.

So, at cold the load is too much for the motor to get to speed before
the centrifugal switch opens. Which means:
1. The switch needs to be adjusted or replaced (adjustment seems highly
problematical),
2. The compressor is putting too much of a load on the motor (can it
degrade in some way to increase the load?),
3. The motor has lost starting power (can the starting cap lose capacity?)

BTW, this is a small IR compressor, "2 hp" motor (15a at 110).

Bob

On Sun, 28 Nov 2004 11:45:44 -0500, Bob Engelhardt wrote:

I have a similar situation: the compressor has a difficult time starting
and if it's cold, it won't start at all (labors slowly along until the
breaker trips). The only way that it starts instantly is if the outlet
from the compressor head is disconnected. I *definitely* ruled out the
unloader and the check valve. BTW - the check valve cannot be the problem
if the unloader is working: the unloader drains the pressure between the
compressor and the check valve. A bad check valve would just bleed down
the tank through the unloader. The capacitors are ok on a go/no-go basis
(not short or open).

The unloader doesn't stay open after cutoff. It opens to relieve head
pressure and then closes. So a leaking check valve will re-pressurize the
compressor.

When I saw "habbi's" post I checked my centrifugal switch. It was
pitted, so I cleaned it. When I tried it, I noticed a lot of arcing
during start (it still didn't start right up). It was "hunting": at
stop the switch is closed and it gets *almost* to speed and the switch
opens. Which causes it to slow and re-close the switch. This repeats.
When it has warmed up it doesn't do it.

The start switch should not be doing "a lot of arcing during start". At
most there might be a brief spark as the switch opens. A bad start cap
would not allow the motor to reach a high enough speed while on the start
windings to be able to run and cause this sort of cycling between the
start and run windings.

So, at cold the load is too much for the motor to get to speed before
the centrifugal switch opens. Which means: 1. The switch needs to be
adjusted or replaced (adjustment seems highly problematical), 2. The
compressor is putting too much of a load on the motor (can it degrade in
some way to increase the load?), 3. The motor has lost starting power
(can the starting cap lose capacity?)

I'd try replacing the start cap. They do weaken with age and are
temperature sensitive, so a dying start cap could cause the symptoms
described. And a for just a few dollars the cap can be eliminated as a
cause. While is possible that the counter balance springs in the start
switch have weakened, allowing it to open early, that's not a likely
failure.

--
The instructions said to use Windows 98 or better, so I installed RedHat.

On Sun, 28 Nov 2004 11:45:44 -0500, Bob Engelhardt
wrote:

I have a similar situation: the compressor has a difficult time starting
and if it's cold, it won't start at all (labors slowly along until the
breaker trips). The only way that it starts instantly is if the outlet
from the compressor head is disconnected. I *definitely* ruled out the
unloader and the check valve. BTW - the check valve cannot be the
problem if the unloader is working: the unloader drains the pressure
between the compressor and the check valve. A bad check valve would
just bleed down the tank through the unloader. The capacitors are ok on
a go/no-go basis (not short or open).

When I saw "habbi's" post I checked my centrifugal switch. It was
pitted, so I cleaned it. When I tried it, I noticed a lot of arcing
during start (it still didn't start right up). It was "hunting": at
stop the switch is closed and it gets *almost* to speed and the switch
opens. Which causes it to slow and re-close the switch. This repeats.
When it has warmed up it doesn't do it.

This sounds like it could also be a weak or bad run capacitor...

So, at cold the load is too much for the motor to get to speed before
the centrifugal switch opens. Which means:
1. The switch needs to be adjusted or replaced (adjustment seems highly
problematical),

Wouldn't worry about it if it's clean and lubed properly, and the
contacts are in good shape. The adjustment shouldn't be too fussy.

2. The compressor is putting too much of a load on the motor (can it
degrade in some way to increase the load?)

Yes - take the belt off, open the exhaust to tank pipes, and walk
the compressor and the motor over by hand. If there's a bearing going
bad on either the motor or compressor, you'll feel it. And see if the
motor starts and comes up to speed OK with the belt off.

3. The motor has lost starting power (can the starting cap lose capacity?)

Yes, and they're hard to test without a special test rig - when in
doubt and/or to be safe, change them both. They're not expensive.

BTW, this is a small IR compressor, "2 hp" motor (15a at 110).

Gee, according to NEC2002, Table 430.148 (pg552) the current draw
for a 2 HP motor is 24A at 115V. A bit much for a branch circuit,
even figuring that the motor should only be hitting FLA as it
approaches the tank's cut-off pressure...

Your "2-HP" motor is really a 3/4 Hp (13.8A) to 1 HP (16.0A) motor,
they must be using the "Sears Horsepower" rating tables. ;-)

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Jim Levie wrote:
The unloader doesn't stay open after cutoff. It opens to relieve head
pressure and then closes. ...

Mine doesn't. Mine is opened by the armature of the pressure switch.
As long as the pressure switch is open, the unloader is open.

The start switch should not be doing "a lot of arcing during start". ...

No kidding?

... the start cap. They do weaken with age and are
temperature sensitive, ...

Ah! That is consistent with the symptoms.

While is possible that the counter balance springs in the start
switch have weakened, allowing it to open early, that's not a likely
failure.

Hadn't thought of that. I doubt that there's any reasonable way to test
them.

Thanks,
Bob

Bruce L. Bergman wrote:

This sounds like it could also be a weak or bad run capacitor...

You're right - hadn't thought of that.

1. The switch needs to be adjusted or replaced (adjustment seems highly
problematical),

Wouldn't worry about it if it's clean and lubed properly, and the
contacts are in good shape. The adjustment shouldn't be too fussy.

OK, it's good to take that off the list.

2. The compressor is putting too much of a load on the motor (can it
degrade in some way to increase the load?)

Yes - take the belt off, open the exhaust to tank pipes, and walk
the compressor and the motor over by hand. If there's a bearing going
bad on either the motor or compressor, you'll feel it.

Ok, I tried that - no problems.

And see if the
motor starts and comes up to speed OK with the belt off.

Yeah, it starts fine just by opening the exhaust.


... can the starting cap lose capacity?)

Yes, ...

Good to know - I would have assumed that they were either good or bad,
with no in-between.


BTW, this is a small IR compressor, "2 hp" motor (15a at 110).

... Your "2-HP" motor is really a 3/4 Hp (13.8A) to 1 HP (16.0A) motor,
they must be using the "Sears Horsepower" rating tables. ;-)

Indeed, to be 2 hp it would have to be 2 * 750 / 15 * 110 = 90%
efficient. Not likely.

Thanks,
Bob

On Sun, 28 Nov 2004 20:18:52 -0500, Bob Engelhardt
wrote:

Jim Levie wrote:
The unloader doesn't stay open after cutoff. It opens to relieve head
pressure and then closes. ...

Mine doesn't. Mine is opened by the armature of the pressure switch.
As long as the pressure switch is open, the unloader is open.

Just as a side note, many commercial pumps, such as IR on some models,
use a rather ingenious "governor" using weights at the end of the
crank shaft to depress a spring loaded valve at the end of the crank
cover, for an unloader.

I recently rebuilt one for a customer where the weight had come loose
and was laying in the bottom of the sump. A new pivot was ground from
drill rod and installed.

Gunner



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