AC troubleshooting

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Old 05-29-15, 03:11 PM
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AC troubleshooting

Hoping to get some help identifying the part/parts I need to get my AC going again.

My unit is a Lennox HS29-024-2P single phase, with a non-scroll compressor. Neither the compressor or the fan are kicking on. After checking the thermostat and breaker, I removed the panel on the unit and started poking around with my multimeter. I have power everywhere I should. The contactor is engaging when the thermostat turns on. The start capacitor doesnt look bad at all. The dual capacitor is pretty rusty, but neither appear to be bulging. I also have a potential relay in there, but Im assuming thats functioning properly as well since I was reading 240v at the capacitors. Im guessing that one or both capacitors are bad, but didnt know if there was a way to test them to figure out which one was causing the trouble.

Its a toasty 88 degrees here in the living room, so any help at all would be greatly appreciated!
 
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Old 05-29-15, 03:54 PM
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You need a multimeter with capacitance reading.
 
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Old 05-29-15, 07:48 PM
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Welcome to the forums.

I would normally have you check for 240vac on the load or A/C side of the contactor but you said you did measure 240v inside.

It's pretty rare for the compressor and the fan parts of the cap to fail at the same time and even then..... the fan or the compressor usually hums until it cuts out on high heat.

I would change the dual cap but I'm not 100% certain that's the problem.
Make sure all the wires are tight on the caps.

Lennox HS29 manual with wirng diagrams.PDF
 

Last edited by PJmax; 05-29-15 at 08:05 PM.
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Old 05-30-15, 10:28 AM
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Glad I found the site and thanks for the responses.

Turns out the connectors on the rusty dual capacitor had some corrosion as well. I gave each wire a good jiggle, then manually depressed the contactor switch outside and it kicked right on..
 
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Old 05-30-15, 10:39 AM
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Turn off the power and clean the connectors well, both the wire ends and the capacitor terminals. If you have poor contact, you have high resistance which generates heat. The terminals could actually burn up. Better to be safe than sorry.
 
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Old 05-30-15, 11:03 AM
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I would replace the cap and clean the wire connections to it.
 
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Old 05-31-15, 11:09 AM
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I just replaced the connectors for the wires and cleaned the cap terminals with a wooden handled wire brush.

I found both replacement cap's at General Supplies Inc for quite a bit cheaper than everyone else. Does anyone have anything bad to say about them or their quality, or should I pull the trigger for a good deal?

Lennox 89M73 35/5 MFD 370V Round Dual Capacitor

Packard PRMJ145 145-174 MFD 330V Round Start Capacitor
 
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Old 05-31-15, 02:10 PM
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When MFD was correct, I always bought 440 volt capacitors; they replace the lower voltage capacitors. Also, stocked them on my vans with different MFD ratings to meet replacement needs.
 
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