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Old 06-10-2009, 12:18 PM   #1
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Help with diagnosis


I have a lennox unit about 15 years old and for the first time my outside unit wont come on. The thermostat appears to be working (blower comes on after setting the tempature) circuit breakers and wiring appear to be ok. What i did find was there is a relay/switch box on the outside unit that i can push and turn the system on manualy every thing works ok. There has to be something that tells this relay/switch to turn on. Any ideas about this problem? Just trying to save some $$$$$$$

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Old 06-10-2009, 12:57 PM   #2
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Help with diagnosis


If the relay/switch box you are referring to is the contactor inside the unit, it could be bad or something upstream of that such as the control board or thermostat.

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Old 06-10-2009, 05:57 PM   #3
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If you have a voltmeter and know anything about electric you should turn your thermostat as low as it goes to bring on A/C.

Go outside and check for low voltage at the contactor( Usually 24 volts)

That is what starts your outside unit on a signal from the thermostat.

If you have it something outside is wrong , if you don't have it something inside is wrong.

Lets go from there.

REMEMBER to read the wiring diagram to be sure you are checking voltage at the right place.
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