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Old 06-11-2012, 11:27 PM   #1
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Lennox HS29-024-2P Central Air Unit doesn't start


I have a Lennox HS29-024-2P Central Air Unit. All of a sudden it just stopped working. Both the Fan and compressor do not start and I donít hear any humming. When standing next to it I can hear and see the contactor click and move when the thermostat is turned on. I donít hear anything else. I tried manually pressing the contactor with a stick and it doesnít do anything. Iím hearing many people talk about replacing the Dual Capacitor. Visually the Dual Capacitor doesnít look like itís bulging but itís slightly rusty. The start capacitor however does look bad, there is white colored stuff seeping out of it. I also verified the fan wasnít stuck as it turns freely. Iím thinking I should replace the start capacitor since itís not very expensive. Should I also replace the Dual Capacitor? Any Suggestions would be greatly appreciated.

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Old 06-12-2012, 04:26 AM   #2
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Lennox HS29-024-2P Central Air Unit doesn't start


Your post is slightly confusing. If there is a dual run capacitor than it starts both the fan and the compressor and there shouldn't be an individual start cap unless only one side of the dual at one point went out and someone simply jumped over to a single rn stat cap for one single component.

Are there wires from one cap connecting it to the other? If so than check the numbers of both caps and compare them. If one of the same numbers is on both than you're not going to need a single any longer, only the dual.

ie: 5 mfd is a common fan capacitor. In a dual run the numbers may be 5/55 +/- 6% and then the single run cap off to the side would be 5mfd (uf)+/- 6%. If from the dual run cap there are wires travelling to the single 5mfd cap than that meant that the fan side of the dual run cap went out so they jumped common over to the new single run cap and used it that way, without having to replace the entire dual run cap.

Take a pic and post it.

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Old 06-12-2012, 06:24 AM   #3
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Lennox HS29-024-2P Central Air Unit doesn't start


That AC came from the factory with a 5-2-1 style hard start kit Doc.

OP... take the top off of the unit, after making sure the breaker is off, and look for chaffed wires. Also take the compressor terminal cover off and make sure the wires are secure to the posts.
Sounds like you have a tripped breaker. If the wires all check out good then it's probably a bad compressor. You'll need to buy a multimeter to check further.
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Old 06-12-2012, 11:49 AM   #4
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Lennox HS29-024-2P Central Air Unit doesn't start


According to the manual it uses a 5/30 MFD 370 VAC Dual Capacitor and a 145-175 MFD 330 VAC Start Capacitor. I did check my circuit breaker and it was on. To be sure I reset it by turning it off and on. I also unplugged and plugged back in the circuit disconnect by the air unit outside.
Is the picture I posted with the original post at postimage org ( http://s18.postimage.org/kbubmqprb/Start_Capacitor.jpg ) not showing up?
The Start Capacitor definitely looks like there's something wrong with it. I'll open the unit up further and look for any chaffed wires or broken connections. Is there some type of internal fuse on the compressor or within the unit? I do have a multi meter but it doesn't check capacitance.

Last edited by Help!!!; 06-12-2012 at 12:04 PM.
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Old 06-12-2012, 11:55 AM   #5
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Lennox HS29-024-2P Central Air Unit doesn't start


Thats the hard start cap and its exploded. Good thing is you can si mply unwire it and its relay and if the other is good run the system.
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Old 06-12-2012, 12:28 PM   #6
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Lennox HS29-024-2P Central Air Unit doesn't start


With the breaker to the condenser off, not just the stat in the off position but the breaker off, remove the black wire coming from the relay to the contactor from the contactor, remove the red wire which is coming from the exploded start cap to the other capacitor and then the yellow
bright wire which is coming from the relay to the silver dual run capacitor. remove that wire at the silver capacitor. No need to remove any wires from the exploded cap or the relay, only remove them from the contactor and the other cap.

Now the hard start kit is entreily removed from circuit. Make sure those loose wires are tied up/electrical taped and not touching anything at all whatsoever, flip the breaker to the condenser on and turn the stat to cool. If it comes on than you're good. Probably best to go ahead and purchase a new hard start kit and install it, though.
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Old 06-12-2012, 12:34 PM   #7
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Lennox HS29-024-2P Central Air Unit doesn't start


The contactor is the very lowest component in your pic, where the three black wires are on the left and the two reds and one yellow are on the right.

The relay is the little lack box directly under the exploded hard start cap with the one black wire on the left and the one yellow wire on the right.

Remove the black wire coming from the relay at the contactor there. Remove the yellow wire coming from the relay at the silver dual run cap. Remove the red wire which is coming off of the exploded cap from the silver dual run cap.

I know I've said this twice now, but in case you didn't know what each component was...

All of these wires should simply pull off, with a little elbow grease. Be careful, try to only pull from the wires and not touch anything else.
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Old 06-12-2012, 05:19 PM   #8
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Lennox HS29-024-2P Central Air Unit doesn't start


With the thermostat calling for cool and the contactor pulled in does your multi meter show 240V going through the contactor? The part about making no noise is making me question if there's power or not. There should be a hum from the compressor every minute or so if it's trying to start with dead capacitors.
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Old 06-13-2012, 04:24 PM   #9
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Lennox HS29-024-2P Central Air Unit doesn't start


I didn't want to do anything with the unit being live and I didn't check voltages. With the breaker off and the disconnect removed I checked the contactor with my multimeter and found it wasn't closing the circuit. After scraping the contactor back and forth a few times it tested as closing the circuit. I put everything back together, turned on the power and it started working again.

I'm going to replace the contactor however I'm wondering if I should use the system until then or would that be bad? Should I still replace the start capacitor and the potential relay and could that be contributing to the contactor going bad?

Thanks again
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Old 06-13-2012, 07:25 PM   #10
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Lennox HS29-024-2P Central Air Unit doesn't start


Marty nailed it! It's probably a good idea to replace that hard start kit. You have the pictures to inform you how to wire in the new one. You can simply remove one wire from the old one's connection and put the same new wire in it's place, one by one. It's very easy. The cap and the relay will come wired to each other, there'll only be the three wires I previously mentioned to hook up.

That relay may or may not be opening once the compressor has started. You can test continuity like you did for the contactor (same exact thing). Relay should be normally closed (showing continuity) without any power and open once the compressor is running. It opens to remove the cap from circuit, hence start cap.

The a/c is fine to run as long as that contactor makes but best to replace it. Get the exact same one and again, simply one wire from the old one to the new one and you're done.

Glad it's working.

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