hard start capacitor

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Old 06-11-12, 07:57 PM
J
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hard start capacitor

Hello, I am trying to select a replacement hard start capacitor (the current one seems to have burnt out) for central a/c. Unfortunately, the label from the current start capacitor has been removed, so no details can be identified. The current run capacitor is listed as 40uF and 440VAC. Does the start capacitor need to match the parameters of the run capacitor? If so, I do not seem to be able to find start capacitors rated at even close to 400VAC... Any help with this issue would be greatly appreciated.
 
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Old 06-11-12, 08:38 PM
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The most common ones used around here are the Supco SPP-5 or SPP-6. Either one should work for most any residential A/C. Simple to install & inexpensive.
 
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Old 06-12-12, 07:03 AM
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Thank you for your response! SPP5 seems to be rated for at least 43uF. Will that work with the 40uF for the run capacitor?
 
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Old 06-12-12, 06:05 PM
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It will work with, but not in place of the 40 microfarrad run cap. The SPP series are start capacitors with an internal relay which causes the start cap to drop out of the circuit once the compressor is running.
 
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Old 06-12-12, 06:52 PM
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The two wire hard start kits ("superboost") should only be used on old compressors which have trouble starting after sitting idle for a long time.

They take a while to reset after each cycle, making them useless for very short power failures.

The 3 wire kits reset right away and get taken out of the circuit as soon the compressor gets up to speed.

See Hard Start Test! Not all Hard Start Kits are the same! - YouTube (warning: some bad langauge)

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If your start capacitor is wired is series with a relay, your best option is to obtain a new 3 wire hard start kit such as Amazon.com: Compressor Saver Hard Start Capacitor Model CSR U2: Home Improvement
 
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Old 06-12-12, 06:58 PM
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Every air conditioner should have a time delay installed either in the unit or via the thermostat to prevent an attempt to restart after a very brief power interuption. Every piece of equipment I install gets a five minute delay on break control.
 
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Old 06-12-12, 09:00 PM
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That's true.

Used to have a unit with an early first generation scroll compressor - it had a 5-10 second delay on make device to prevent it from running backwards in the event of a very short power interruption. Oddly enough, it happened a couple of times. (loud, low pitch noise)
 
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Old 06-14-12, 05:54 PM
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My unit (20+ year old Janitrol 12 SEER) has a first generation scroll with about a 15 second delay. I added a digital stat with a five minute delay exactly for the prevention of the running backward problem.
 
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