I would not bypass the safety because I don't want the heater to blow up or something but you guys are right, some people might try. I disconected the 'G' wire from the thermostat and the blower still runs.
Question: I tested the Limit, primary, gas (Labeled S10). It is located right after the 24V side of the transformer. It seems like this should be a normally closed limit switch because it provides power to the red wire of the thermostat. I removed the Limit, primary, gas and put an ohmmeter on it and the circuit is open. I guess this should be replaced?
I still do not no why the blower would be running especcially since all the thermostat wires have no voltage. I guess the Blower circuit board has a short or something. The board looks clean, no blacks fault marks, but the blower should not run with no 24V power to the blower relays? I guess I will replace the blower circuit board also.
I will replace the Limit, primary, gas and blower circuit board unless someone can help with this problem.
never never bypass a safety!!!! peoples lifes are at stake!!!!
May as well check your filter.
Normally the safety switch the techs here are refering to fails due to low airflow caused by dirty filter, too many supply vents closed, and a whole list of other probs a tech would have to check for.
You can go ahead and check those for now.
It won't bring your heat back on, but at least you'll have it ready to go when the tech gets your heat back on.
<<<<I will replace the Limit, primary, gas and blower circuit board unless someone can help with this problem. >>>>
And you'll get the parts from?????
Most Lennox parts are proprietary and relatively expensive. Even if you could buy the parts yourself, getting a professional to correctly diagnose and change the one broken part will probably be cheaper than buying a bunch of parts yourself and replacing stuff until the furnace works again. CALL A PROFESSIONAL. If it IS a limit switch, you need to find out WHY the limit tripped and correct the problem, not just replace the part and hope it dosen't fail again.
Don't panic everyone....
He went to Staples and got a Big Red Easy Button
If only they had one to keep me from having to go through years of training... not to mention still learning everyday. :D
Ok... here's the step by step....
Check your rectification circuit to make sure your getting an amp reading through your ac to dc back to ground
make sure your ground is grounded and the line going to the meter outside hasn't been changed over to the new plastic stuff they like to run underground now. If it is, you might not have a good ground rod circuit and stray voltage will fool your rectification circuit.
If the ac circuit does not have the proper E then check to make sure nothing is touching it and clean it off. You know how they get all crudy and stuff when its running.
Also check to make sure the induction amps are ok and the microfarads. You know how pesky them farads can be. Sometimes you need 5 and end up with 4.2 and it overheats the windings and the thing shuts down on overload.
If all thats ok... then check the delta t and make sure its in the right range.
better make sure your static is ok too. there could be a little too much restriction and cause a loss in cfm causing high delta t.
If thats ok.. use your manometer to check the manifold pressure and just to be sure clock the meter and make sure your not overfiring
If it is overfiring, do a smoke pencil test to make sure your not getting smoke blowing out where the inshots are
If there's smoke blowing out with the fan on, then you have a bad heat exchanger.
If all thats ok, check the pressure on the vac switch unless it has a centrifical switch then check to make sure it closes when it should
if it don't then check the microfareds on the inducer
if thats ok check the wheel
if its ok check the pressure on the flue to make sure its enough negative pressure. That is of course if its B vent.
By the way, B vent is ok to make a test port in to check CO2 levels and O levels. While you check that, be sure to do the effeciency check. If its less than 80 then you might have a prob with the inshots. If thats the case take them out and hit em with a steel brush. I kinda like to do it anyways so the bridges are clean. And it will make a good circuit for the rectification.
Oh yeah.. if it was a limit, take a K thermister and check the T and make sure that when its operating that the t don't go higher than whats listed.
Lemme know if you get all that checked out....
If you haven't figured it out by then, then you might have a bad board. But make sure you have input E cuz without in E you wont have out E. Then again, you might not have E at the 10:1 step down. If you dont then ohm out see what side failed. If its the pri then check your N's everywhere, if they get loose something might fry. If its the sec then get the R's everywhere. Did your stat try to bring on the air anytime during the night? If so check to make sure your 18-2 is ok. Sometimes the electromagnet don't pull in either and it makes it pull too many I's and that'll do it too.
Before you leave.... go ahead and check the FPM's at the RAG and convert it into CFM's with the manufacturer's AK factor to make sure you got the right cfm's per ton.
But to check it all you'll have to go pick up all the right meters.... I think maybe around $2000 should get you something that will get you by.
Did I miss anything guys?
Oh yeah... if that dont' work.. flush the toilet 3 times
to get rid of all the crap I just fed ya hehe
ON a more serious note...
The site rules state step by step DIY questions.
[Edited by wormy on 04-07-2005 at 01:36 AM]
fan is running constantly because limit switch is open. that is what it is designed to do.
Thanks to some people for their help. Others just think everyone is ignorant and have no clue what they are doing.
It was the limit switch. After I saw the wiring diagram it was pretty easy to diagnose. I did a couple checks with the volmeter and noticed I was not getting power threw a limit switch. Turn system off, put an ohmmeter acrossed it and it was open. I purchased a new one and installed it and everything works fine. I think is was an over dirty filter. I set the thermostat for 90 replacement and it just went the 90 days. I guess I should check and change my filter more often. I have been doing a lot of work on the house, so maybe it got extra dirty because of that. Not sure but will keep a better eye on the filter from now on.