Lennox Elite not working right

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Old 06-09-08, 07:22 AM
jn
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Lennox Elite not working right

I have a Lennox Elite series (surelight) G26Q3-50
At the thermostat I set it to cool and fan on auto. I set the temp to lower than the current temperature so it should turn on the A/C.
The only thing that happens is the combustion blower kicks on and runs continuously. The diagnostic LEDs just continue to both slowly flash (like normal).
The condensor outside does not turn on and the big blower never comes on.
If I change the thermostat fan setting to on, the display on the thermostat goes blank and the condensor and blower will kick on and run continuously and never shut off until I switch off power at the air handler or change the fan setting on the thermostat back to auto.
I tried heat and it is basically doing the same thing. With the fan on auto at the t-stat I just get the combustion fan continuously running.
Any ideas????
 
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Old 06-09-08, 11:27 AM
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Did we just install a new t-stat?? kinda reading between the lines here but that is my best guess. Most likely you will need to just study the instructions a bit and of course utilize that hand drawing you made of all the wiring connections on the old t-stat, you did do this BEFORE you disconnected the old one RIGHT?
 
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Old 06-09-08, 11:51 AM
jn
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No... no new parts here.
This unit was installed and functioned fine since Oct. 2001
The only thing I have done is replace filters every couple months and hose off the condenser every now and then.
This is a secondary unit for a large home and is used to heat / cool the upstairs.
I have the same t-stat on both units so I did try unplugging and swapping them but it acts the same and the problem isn't fixed by changing out the t-stat.
The wiring stays mounted to a back plate and the t-stat unsnaps and unplugs from that plate. All the wiring colors matched and were connected well under the mounting screws.
I think I will take a look at the circuit board on the larger working model and see if it matches the smaller one. I may be able to swap boards to see if it helps.
Any other ideas????
 
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Old 06-09-08, 12:49 PM
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Yes if they use the same control board that would be the next item to check, swap them out if they are identical and see what you. Lots of times they upgrade boards every few years so make sure and buy the latest upgrade that has all the bugs worked out.
 
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Old 06-10-08, 06:26 AM
jn
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Figured it out.
It was the thermostat after all.
I pulled the t-stat off the wall and shorted the red to yellow and it immediately fired up the A/C.
I was wondering why when I swapped them it didn't seem to act right.
I read a little in the thermostat manuals and discovered that if power is off, and then comes back on (or if you unplug a t-stat and plug in a different one as I did) it will not let the units cool for 5 minutes and will only briefly power the combustion fan. They descibed it as a safety feature to keep from turning the compressor on and off repeatedly when power is flickering. I guess they also drive the combustion fan in case there is any left over gas if power shuts off while heating. Whatever...
After hooking the wires back up with a good t-stat, waiting 5 minutes... then all was good.
Glad I didn't swap those boards yet!
 
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