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
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