Central Air Not Working!


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Old 05-28-09, 02:34 PM
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Central Air Not Working!

6 year old Lennox HS29 cooling unit. Unit is getting power to the outside, so I replaced the capacitor. That didn't do it, any suggestins? It makes no noise outside whatsoever. Is there another starting capacitor on this or am I looking at a motor? I'm not good with a multimeter but I can try...suggestions?
 
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Old 05-28-09, 03:51 PM
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Look at the contactor [the big relay] do you 240 volts going to it fom the disconnect switch? When you turn the thermostat on to make the cooling run, does the contactor pull in and close its contacts? If yes, do you have 240 volts leaving the contactor going to the circuits in the unit? If no, do you have 24 volts at the magnetic coil on the contactor?
 
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Old 05-28-09, 04:31 PM
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Thanks for answering my post! No, the relay does not open or close when the unit is powered on. Are you suggesting it could be the relay? I also have a Honeywell programable thermostat that for some reason I have never felt worked correctly. Since the unit is getting power (at least to a point) could the thermostat be an issue. Thanks again.
 
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Old 05-28-09, 05:10 PM
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How do you know you are getting power to the outside unit if you do not hear anything and you are not good with a voltmeter? Or do you have a voltmeter and at least made a test to see you had 240 volts out there?

You have to have both 24 volts ac and 240 volts ac out there. The 24 volts gets sent out there by the thermostat in the cooling mode, which then triggers the 240 volt contactor to let the 240 volts through.
 
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Old 05-28-09, 06:14 PM
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I know I'm getting power because I have a tester that senses electric current, so I know I have power at the capacitor. I'm thinking of replacing the thermostat and the "relay" to see if it's either. Still less than a service call. Thanks for your help, and any other suggestions you have to offer.
 
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Old 05-28-09, 06:51 PM
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There is a certain progression you should go through...

First of all is this a straight air conditioner or a heat pump?

Take the face of the thermostat off. Make a jumper wire and put that wire between the R and Y terminals. Does your outdoor unit come on now?

If it does when you jump it out but does not with the t-stat on, then t-stat is the problem.

Does the unit have safety switches (loss of charge or low pressure switch)

The contactor has a small copper coil of wire. On either side of this coil will be a wire attached to the coil via a quick connect fitting.

With you meter you need to verify if you're getting 24 VAC to it. If not then there are other things you need to try.

I'd use caution if I were you, you're dealing with lethal voltages and if you're not careful you can cause more problems to your system then you'll have to call a tech
 
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Old 05-28-09, 07:48 PM
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are you using one of those non contact voltage testers?
 
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Old 05-28-09, 07:59 PM
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the high pressure switch

look at the unit outside and remove the panel cover where the wires go into the unit from the disconnect switch, you'll see the compressor in there its a large black can looking thing that has a pipe about the size of your pinky, not far from where its piped to the compressor you'll see a plastic shaped container like an RX script bottle with a red button covered in a rubber sleeve, depress it and see if it starts now. If it does, the outdoor fan likely won't start or will stop shortly...
 
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Old 05-28-09, 08:20 PM
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are you thinking SOV not getting energized?
 
 

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