Heater wont fire up

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  #1  
Old 06-20-09, 05:46 PM
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Heater wont fire up

I know I don't need it know but I messed with it and now it doesn't work. Had repairman come check my ac as it doesn't keep up and the heat/air from the vents doesn't blow well. He said charge was low and that should take care off it. I didn't notice much of a difference but he said its fine. Not liking this very much. I asked him if the evaporater coil could be dirty and he said no. So when he left I got brave and decided since no one has looked at the furnace or air the previous six years I would clean it.

I pulled the blower motor for the furnace out, and it was caked in dirt. I looked down the duct and could see the A coil was dirty also. So I cleaned the blower motor out with a air compressor and oiled the spots the sticker said should be done every 3 years. Ac works as well as it did, but now furnace wont fire up. I have one blue wire left that I think goes on the back off blower motor with the other blue wire but I am not sure. Here are some pics. Hope you all can help me.

Dirty a coil. Front is where I vacummed some dirt up. Calling repairman to clean it as I cant get the other side exposed to clean it.


This is the board in my furnace. Honeywell ST9120A-H


This blue wire on this piece ( have no idea what it is) that goes to C is unplugged and that is where I am lost.




Lastly the schematics. I got everything else hooked up right. But am lost on this blue wire. If anyone can help it would be appreciated.

 
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Old 06-21-09, 06:55 AM
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I put on my #100 power reading glasses from the 99 cent store to read the schematic. The blue wire in question seems to go to what's called an interlock switch. The switch has a black wire connected to the other side of it which goes to the field connection box.

There is a better schematic:

http://www.google.com/url?sa=t&sourc...BT-x9MklXHCFTg
 
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Old 06-21-09, 11:21 AM
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Hmmm- you are saying that the blue wire on C terminal of the round device [the pressure switch] is disconnected at its other end? Must be something wrong with my glasses because in the pictures I don't see the disconnected end. One of the blue wires goes to a switch called the aux limit, the other one goes to the 24v terminal on the ignition module. The ignition module IS NOT the HW ST9120. The cooling coil is really dirty. Call a different repair person because now your system is probably overcharged with freon. How much did the dolt put in?
 
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Old 06-22-09, 01:41 AM
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Yes the blue wire from the c terminal on the pressure switch is discconnected on the other end. I didn't unplug any of the wires below only the ones on the fan control. As far as the aux switch, is it possible its on the backside of the blower motor shroud? There is a blue wire coming off the back of the blower motor shroud with some kind of sensor on it. It has two connectors on it but when I slide the motor shroud out there was only one blue wire connected. It could easily have had 2 wires on it and when I pulled it out one popped off without me seeing. If that is the case would it matter which side the wires got connected to the aux switch? Or do they just need to be connected to complete the path? Also do you think this could be the reason why my air conditioner can't keep up?

I have no idea how much charge he put in the AC.

I think this guy was looking for a quick $75.00 Again any ideas you guys give is really appreciated. I might have to pay someone to come look at the heater but I think I figured out what was wrong with my air.







 
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Old 06-22-09, 06:56 AM
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I think you have figured out the problem with the blue wire. An aux limit is usually for downflow applications but since most furnaces are multi-position, the manufacturers just put in all the controls that will cover any application. That coil is filthy. What you don't realize is it's clogged all the way thru the depth of the of the coli and surface cleaning won't get it. What's below the furnace? Basement and ductwork? How much refrigerant did he write on the service ticket?

If one of my former students ever went on a job and blew that diagnosis, we would have to call the extraction team. They're the ones who would extract my boot from his/her posterior. I can't believe the guy missed a coil that dirty.
 
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Old 06-22-09, 07:32 AM
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Well repairman number 3 came and left. He about crappped when he saw how dirty the coil was. He said he doubts the last guys readings were right with the coil that dirty. He asked if the other guy put any freon in and I said that he said he did, but didn't say how much. A floor register that I used to have to put my hand 3 inches from to feel any air coming out of, I can now feel air up to my armpit standing up ( Im 6ft tall). Needless to say I am very pleased with the work. Hopefully its not leaking. Going to replace both with income tax next year for some newer more effecient models.

Anyway about this blue wire, lol. I do think that the aux switch is the switch on the back off the blower motor shroud. One end of the wire goes to the ignition module I believe it is called. Then goes to the pressure switch. Then goes to the aux switch which then runs back to the fan board. If I had the blue wires flipfloped on the aux switch connectors would this stop it from starting? Or does it now matter? Again any ideas or thoughts are greatly appreciated.

Oh below the coil is a crawlspace. Slab home.
 
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