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Electrical Code - USA Commercial or Residential 1999 / 2002 / 2005 versions - for UNITED STATES

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  #1   IP: 66.30.155.131
Old July 24th, 2008, 12:25 PM
jackmo jackmo is offline
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Default Hard start kit for AC unit

I recently had central air installed. I noticed that when the compressor starts the lights dim for a second. I talked to the guy who did the install & he suggested he put a "Hard Start kit" in. Do I need this?
How does it work?

Thanks in advance, great site!!

Jackmo
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  #2   IP: 75.84.128.60
Old July 24th, 2008, 12:53 PM
sloooo sloooo is offline
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A hard start kit is basically a start capacitor that has a relay attached to it. Your compressor has 3 windings on it. The start winding, the run winding, and the common winding. What your run capacitor does is create a favorable phase shift of the incomming power across the start winding so it kind of gives you that 3 phase power, but with only 2 hot legs. This allows the compressor motor to start turning. If you have ever seen a motor that has a bad run capacitor, it will just hum until it trips on the internal overloads. What the hard start kit does is kind of the same thing the run capacitor does, but it discharges a quick pulse of power, usually a second or two, and it get's your compressor up to speed much faster than just a run capacitor.

If you have lights dimming when your compressor comes on, by all means add one. I will not install a condensing unit without already including one in my bid. It will increase compressor life and not put a strain on your electrical back to your panel because your not drawing locked rotor amps like you did with out the hard start kit.
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  #3   IP: 66.30.155.131
Old July 24th, 2008, 09:29 PM
jackmo jackmo is offline
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Sloooo,

Thanks for the info, especially the explanation of how it works.

Jackmo
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  #4   IP: 75.84.128.60
Old July 24th, 2008, 11:33 PM
sloooo sloooo is offline
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That's what these forum are for If you have any other questions, please come back!!
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  #5   IP: 66.30.155.131
Old July 25th, 2008, 05:51 AM
jackmo jackmo is offline
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Sloooo,

I am here everyday, I monitor a couple of different forums here & I am amazed the depth of knowledge and the willingness of people to help. What I don't see here is the snotty attitude you see on some forums from people who know towards people who just want answers!
I am a Machinist by trade so I really appreciate the answers that explain things in detail.

So I would like to thank all the people who contribute to this forum as well as the people behind the scenes who make this forum work.

Jackmo
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  #6   IP: 66.30.155.131
Old July 25th, 2008, 11:48 AM
jackmo jackmo is offline
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Default Another question

I am curious why some AC units require hard start kits & some don't.
I have a 200 amp service. The only large electrical item is the electric dryer the rest is lights,TV's & computer.

Thanks,
Jackmo

Last edited by jackmo : July 25th, 2008 at 06:15 PM. Reason: clarification
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  #7   IP: 142.165.236.103
Old July 25th, 2008, 04:30 PM
Total Total is offline
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Quote:
Originally Posted by jackmo View Post
I am curious why some houses require this & some don't.
I have a 200 amp service. The only large electrical item is the electric dryer the rest is lights,TV's & computer.

Thanks,
Jackmo

future expansion or in my city 200 A is the stadard size now ..
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  #8   IP: 24.197.243.146
Old July 25th, 2008, 08:49 PM
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fordrules fordrules is offline
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Slooo has some good info there. This is the brand I install:

http://www.johnstonesupply.com/corp/...t_Code=B16-902

The 5-2-1 kits seem to work very well. I haven't had much luck with supco or some of the others.
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  #9   IP: 75.84.128.60
Old July 26th, 2008, 03:15 AM
sloooo sloooo is offline
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Quote:
Originally Posted by jackmo View Post
I am curious why some AC units require hard start kits & some don't.
I have a 200 amp service. The only large electrical item is the electric dryer the rest is lights,TV's & computer.

Thanks,
Jackmo
Its not the fact that some units require them. Some compressors are tighter than others. But past that is the fact that if you live in a warm area, your system might ask for cooling before your pressures equalize. Single phase compressors are VERY tempermental. Most compressors can start with some pressure difference between the high and the low side.

By this I mean, than when your system is running, your low side pressure could be around 70 PSIG while your high side pressure might run between 250 and 350 PSIG.

Alot of compressor will lock up if there is not a equalization of pressure from the high side and the low side. A single phase 208/240 compressor will start with an imbalance of pressure at about 80 PSIG. That means, if your low side is about 100, your high side better be around 180. New T-stats have a 5 minute time delay to allow the system to equalize.

So, as far as houses that require it, if you have an AC, I would require it. BUT, the common home owner looks short term and not long term. If you were to have an AC guy come put a hard start kit on, it might cost you $150 to $200. BUT, the compressor will last much longer and you'll be lowering the cost of electricity...a little, but every penny helps.

When any motor starts, its what we call locked rotor amps or LRA. If you can get any motor up to speed faster, you lower the LRA of that motor, thus saving you money in the long run. It's not alot, but it is something.

Bottom line is that every AC unit in all homes should have a hard start kit. I know people are going to argue, but do your homework. If a company can save $20 every time they build something, they will. But EVERY compressor manufacture recommends a hard start kit. Look it up and let the argument begin

Last edited by sloooo : July 26th, 2008 at 03:22 AM.
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  #10   IP: 75.84.128.60
Old July 26th, 2008, 03:34 AM
sloooo sloooo is offline
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Quote:
Originally Posted by fordrules View Post
Slooo has some good info there. This is the brand I install:

http://www.johnstonesupply.com/corp/...t_Code=B16-902

The 5-2-1 kits seem to work very well. I haven't had much luck with supco or some of the others.

The kit you use a a PSC kit. That is a 3 wire install kit and I would ONLY recommend it if your comfortable with electricity. Supco is the leading supplier or hard start kits. They make a 2 wire kit that is 6000 BTU to 120000 BTU, and I have had zero issues. That means I can have 1 hard start kit that covers a half ton to 10 tons.
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