# Lennox A/C unit not starting



## SKIP4661 (Dec 3, 2008)

Those wires on top of the compressor are for an thermal overload protector. Have replaced a few those. Do you have voltage across the 24v connections on the contactor. Another way to check is to bypass the overload, If it runs the overload is bad. However I do not recommend running the unit with the overload bypassed except for testing purposes.


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## qbert (Mar 23, 2009)

sounds like you could have a bad contactor. From the pics i see no pressure switches. Test the contactor coil for ohms, see if the coil is open.


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## qbert (Mar 23, 2009)

contactor should still pull in and fan should run even if ol is open


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## SKIP4661 (Dec 3, 2008)

Won't pull in on this model if the overload is bad. It's wired in series with the contactor low voltage wiring. Check out the first pic, you can see the low voltage connected to the blue wire.


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## netddd (Jun 14, 2009)

Well, that does make perfect sense. Since the fan went out last season, it may have caused it to overheat. And yes, it is wired in series. I'll stop by the store tomorrow if I can get out of work early (otherwise tuesday evening) and pick up a replacement. I'm assuming it's field replaceable with some silicone or glue or something. I'll post afterwards and let you know how it went.

Thanks

Dominique


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## ampguy (Aug 16, 2010)

Had a related issue with my Lennox HS29-024, thought it was the 35/5 dual cap, so I got a new one and replaced it (2nd time in ~10 years, life of unit), and still no go.

prodded the contactor switch which is spring loaded, and appears NO (normally open, with springs pressing outward), and fan and A/C went on fine.

Then checked the tstat lines and wasn't getting 24V (or anywhere near).

Went back inside and traced from tstat down (what a rat's nest we have, tstat lines flow through several walls, and split off at furnace for fans and humidifiers), and finally got the thing running.

What I haven't figured out is if there is supposed to be a reset switch for one or either of these sides of the contactor switch. Can't see any buttons to press. Seems like with the condensor being outside and the contactor not sealed so well, that relying on the low tstat vac to close the spring NO switches could be a reliability problem waiting to rear it's ugly head again.

I blew it off with compressed air, along with some spiderwebs in there, but am wondering if I should keep a spare connector handy, along with the normal 35/5 - 440 cap?

Thanks for any thoughts on this.


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## Haldog (Aug 17, 2010)

Normal for 24-V from t-stat to be all that is required to close the contactor. You won't find a reset switch as there isn't one. May find one on the transformer in the fan coil though.


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## ampguy (Aug 16, 2010)

*Thanks*

All is well now, but I wonder what the glitch was that stopped it. Anyways, have traced 24 VAC from tstat through walls to furnace/blower and it's all good now. May replace the tstat since we never ever use the fancy features of this programmable honeywell, and I'd love to have a simpler one.

Thanks.



Haldog said:


> Normal for 24-V from t-stat to be all that is required to close the contactor. You won't find a reset switch as there isn't one. May find one on the transformer in the fan coil though.


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