I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:

General Electric
79F9895
Capacitor, dual, motor starting
5UF/45uF, 370VAC
51/2 x 2"

was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.

Lewis

Hi, Lewis. No, thanks - I've encountered those bad motor caps before.

There are often three caps: a run-cap and a start-cap for the compressor and a run-cap for the fan.

I'll guess that it was a run-cap, either it or the motor was drawing excess current. If it were the start-cap, the compressor wouldn't have started at all.

Is the A/C OK now?
Doug

:I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:
:
:General Electric
:79F9895
:Capacitor, dual, motor starting
:5UF/45uF, 370VAC
:51/2 x 2"
:
:was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.
:
:Lewis
:

:Hi, Lewis. No, thanks - I've encountered those bad motor caps before.
:
:There are often three caps: a run-cap and a start-cap for the compressor and a run-cap for the fan.
:
:I'll guess that it was a run-cap, either it or the motor was drawing excess current. If it were the start-cap, the compressor wouldn't have started at all.
:
:Is the A/C OK now?
:Doug

The cap is in two sections, each showing totally open with a DMM. It looks like a large multi-section cap you would find in an old radio, except the connections slide onto lugs built into insulators on the end of the cap. This end is bulged out as if the internal pressure built up from heat. The running winding (I assume) was acting as if it had a locked rotor (hundreds of bucks), and the fan wasn't doing anything. I pushed the contactor with my finger, and got a loud hum, followed by a BIG arc when I let go. As the cap was shown as two separate caps on the schematic, I couldn't figure out why both motors were not running. When Ilooked at the capacitor and saw it was one unit, the fog began to lift and started me on the road to sucess. As to the A/C working, it is doing great. Seeing how the temp outside is 90 at 9:30 EDT, this would be sent from an air-conditioned all night movie if it weren't. I just thought it was funny we were writing about AC on caps just the other day, and now I have changed the first one in my life, not counting the airline where we would change motor, cap, and anything else to get it fixed, and let the shop fix exactly what was wrong.

Lewis
:
::I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:
::
::General Electric
::79F9895
::Capacitor, dual, motor starting
::5UF/45uF, 370VAC
::51/2 x 2"
::
::was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.
::
::Lewis
::

The motor starting and run capacitors in an air conditioner or in some furnace fans are simply non-polarized electrolytics (in many cases). If leakage develops within the capacitor, it heats up. Steam builds up and blows the seal (or explodes the can). You should see a hole where material leaked out. Once the capacitor dries up, it no longer conducts. It will read as an open circuit unless there is metal touching inside.

The air conditioner was probably cycling off and on because a thermal protector was protecting it (like a circuit breaker, but self-resetting). Some central air conditioning units just have fuses or circuit breakers. I believe that my parents' unit has cylinder fuses, though it may also have a thermal protector built into the unit.

Motors will behave like they have a locked rotor when powered without a rotational field, especially if the regular field coil is large, such as in a high power device like your air conditioner. If you remove the shaded pole windings in a shaded pole motor, it will just sit there and hum, and will be difficult to rotate. If I was to disconnect the start-up coil in my Westinghouse pancake motor fan, the motor would just hum, and would be difficult to rotate. The start-up coil in this fan, the shaded pole windings in a shaded pole motor, and the capacitor operated winding in a capactior-start motor, are all windings which are out of phase with the regular windings, and provide a rotating field when mixed with the regular winding. Once the motor is rotating near its synchronous speed, or at least much more than barely spinning, the main winding is all that is necessary to keep it revolving (in most cases....some motors leave the capacitor coil on all the time).

Thomas

:The motor starting and run capacitors in an air conditioner or in some furnace fans are simply non-polarized electrolytics (in many cases). If leakage develops within the capacitor, it heats up. Steam builds up and blows the seal (or explodes the can). You should see a hole where material leaked out. Once the capacitor dries up, it no longer conducts. It will read as an open circuit unless there is metal touching inside.

The end of the cap where the leads connect bulged out about one-half inch, disconnecting the wires that connect to the terminals, I reckon. Then, as you said, without rotation, it might as well have been a locked rotor. A locked rotor(broken connecting rod) cost a buddy of mine 900 bucks, I got mine running for twenty. Sometimes, ya just gotta blow yer horn a little!!!

Lewis

:
:The air conditioner was probably cycling off and on because a thermal protector was protecting it (like a circuit breaker, but self-resetting). Some central air conditioning units just have fuses or circuit breakers. I believe that my parents' unit has cylinder fuses, though it may also have a thermal protector built into the unit.
:
:Motors will behave like they have a locked rotor when powered without a rotational field, especially if the regular field coil is large, such as in a high power device like your air conditioner. If you remove the shaded pole windings in a shaded pole motor, it will just sit there and hum, and will be difficult to rotate. If I was to disconnect the start-up coil in my Westinghouse pancake motor fan, the motor would just hum, and would be difficult to rotate. The start-up coil in this fan, the shaded pole windings in a shaded pole motor, and the capacitor operated winding in a capactior-start motor, are all windings which are out of phase with the regular windings, and provide a rotating field when mixed with the regular winding. Once the motor is rotating near its synchronous speed, or at least much more than barely spinning, the main winding is all that is necessary to keep it revolving (in most cases....some motors leave the capacitor coil on all the time).
:
:Thomas

:I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:
:
:General Electric
:79F9895
:Capacitor, dual, motor starting
:5UF/45uF, 370VAC
:51/2 x 2"
:
:was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.
:
:Lewis
:

::I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:
::
::General Electric
::79F9895
::Capacitor, dual, motor starting
::5UF/45uF, 370VAC
::51/2 x 2"
::
::was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.
::
::Lewis
::I would be careful opening up and old capacitor, It could still hold a powerful electrical charge,and some of the older caps had PCB's in them that could cause cancer...possibly.

:::I noticed my lights were dimming slightly every 15 or so minutes, as if a heavy load were being applied to the outside AC intot he house. Then I noticed the house getting warmer, as this is Georgia and the temp outsice was 98 and climbing. Checked the compressor/fan box outside, and it was cycling for a couiple of seconds every 15 or so minutes. Started checking and found that a capacitor:
:::
:::General Electric
:::79F9895
:::Capacitor, dual, motor starting
:::5UF/45uF, 370VAC
:::51/2 x 2"
:::
:::was bulging and when I chedked, it was an open circuit on both the fan and compressor sections. Went to get gas in my truck (air conditioneds), and noticed an air conditioning truck parked at a house in my neighborhood. Knocked on door, bought a cap from him, installed it, when I turned the A/C the temp was 95 inside. If anyone wants a shot AC capacitor to autopsy and let us know how it is built, you can have it.
:::
:::Lewis
:::I would be careful opening up and old capacitor, It could still hold a powerful electrical charge,and some of the older caps had PCB's in them that could cause cancer...possibly.

I have decided that the shiny capacitor would be better used as a target for my target rifle. A 100 yard dissection should be safe enough. The A/C was made post-PCB, and I have discharged enough caps to know about charges. I used to repair strobe lights on airliners, they have around 300 UF at up to 400 Volts. One learned fast.
Lewis