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Old 09-28-2008, 08:53 PM   #16
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Diag 11 says:
Main Blower Failure:
This flash code occurs when the main limit opens and fails to reclose within 5 minutes, indicating that the blower motor or blower wheel has failed.

Now, the blower worked fine, but it came on immediately upon turning the switch on. I am thinking that there is a problem with the tstat.

Also curious if the "main blower" refers to the SA fan, or the combustion exhaust fan....

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Old 09-28-2008, 10:42 PM   #17
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Did you turn on the on/off switch on the gas valve (if applicable)?? Shouldn't cause a code 11, but possibly could. Needs to be on anyways.

Main blower is the main blower, the one the moves air throughout the house . The combustion exhaust fan as you called it is the draft inducer motor, which should give a different code if failed.

Check your manual or the furn label and see if it says anything about what the furn will do if power is lost, then re-established. Some just turn back on and wait for the stat, some do a 30 to 90 main blower run before going into 'stand-by'. Some will do the 30 to 90 blower run upon power up only if there also is a call for heat.

Mind you, I am not looking at your furnace so I can't say exactly where things are. Your label states code 11 means main limit opens and fails to reclose within 5 minutes. This limit switch should be mounted on the plate that holds the heat exchanger, has 2 wires (usually red) connected to it, and usually has a rectangular mounting plate. The gas is fired into the ports at one end of the heat exchanger, and the draft motor covers the other ports of the ht exchngr. The draft motor and gas train/nozzles are also mounted to the ht exgr plate. In between them you should find the limit switch. If you disconnect one wire, you can do a continuity test. The switch should be closed (less than 0.1 ohms).

A test you can do to determine if the stat (or stat wire) has a problem. Let's take it out of the equation and fire the unit up manually. Turn the unit off. Take off the blower compartment door, then remove the t-stat wires from R & W. Put a small jumper wire on the W terminal, long enough to reach the R term. Hold the door switch in, turn the unit back on. The main blower may or may not start...depends on what the system normally does upon power up (as mentioned above). My guess is it shouldn't. If all is well at this point, touch the jumper to the R terminal. It should immediately start the inducer, shortly thereafter start the igniter (if HSI) then open the gas valve and start the fire. After the fire starts, a short bit later the blower should start. The fire will burn as long as R & W are jumped. After you are satisfied that things are working well, remove the jumper from R...the fire will go out and the blower will run a predetermined amount of time.

Hope this helps, check the switch on the gas valve, and all wire connections, especially at the board and the limit switch first.
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Old 09-29-2008, 08:03 AM   #18
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Thanks Bill,

Will try that tonight.
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Old 09-29-2008, 10:48 AM   #19
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Bill ?? LOL...Kyle. Bill the Cat is my alter-ego, first thing in the morning...pre-coffee...
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Old 09-29-2008, 12:29 PM   #20
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It's funny, I have not thought of Bill the Cat in years, then I saw your avatar, and the memories came back. Had a friend that used to draw stuff like that all the time. too funny!
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Old 09-29-2008, 02:16 PM   #21
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I did not add this info as I did not think it was pertinent to the non-tstat start-up but it is still more info.

My woodstove has two 8" ducts that tap into the furnace duct SA plenum. Currently, only 1 duct is connected to the plenum, so there is a 8" opening.

The more I think of the "Main Blower Failure", I think that it relates to a lack of achieved static pressure on the system. This became apparent when I tried the system last night and while it was running (for 5 minutes), the red light flashed 4 times, which, according to the manual means:
"High limit switch open or 24 Volt fuse is open. This may be caused by a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow or an open fuse on the control board."

Well after reading what I just read, maybe it is not true. Seems that the error would be for high static pressure, not low....

Again, this does not explain the running of the fan with no tstat, but I will confirm tonight. Also will check that fuse...
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Old 09-29-2008, 05:03 PM   #22
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Quote:
Originally Posted by javan View Post
...Again, this does not explain the running of the fan with no tstat, but I will confirm tonight. Also will check that fuse...
It does if the fuse is blown, or the limit sw is open. There isn't any 24V to hold the relay open to keep the fan from running. Since you haven't fired it up yet, I doubt if the limit sw is open, but it could be. Defective would be the first thing that comes to mind if it is.

I would first check the fuse, then the limit switch. After 24V is made by the x-frmr, it goes directly to the fuse. If it's blown, nothing that uses 24 will work. The computer is looking for 24 going to the limit switch and back before it starts normal operation. Of course, with a blown fuse it'll never get it, nor with an open limit switch.

As far as what you mentioned about static pressure being part of the problem. I doubt it. I've taken new and old furnaces both, hooked them up temporarily with only a gas line and a extension cord for temp power, and fired them through their paces without any problems. No return air duct work, no plenums or supply air duct, no t-stat...straight out of the box.
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Old 09-29-2008, 05:22 PM   #23
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Quote:
Originally Posted by javan View Post
...the red light flashed 4 times, which, according to the manual means:
"High limit switch open or 24 Volt fuse is open. This may be caused by a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow or an open fuse on the control board."
The high limit switch will open if it gets too hot around the heat exchanger. Some casues are as your manual stated....a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow. Some limit switches close by themselves when they cool down, some do not. The fuse doesn't blow just because the limit switch opens (unless it's shorted to the chassis frame).

If the fuse is blown, investigation needs to be done as to why. Maybe a cut wire somewhere?? Is the 120V hooked up correctly, grounded and proper polarity? (Shouldn't blow the fuse, but the machine may not run right either)
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Old 09-29-2008, 08:27 PM   #24
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Loose connection on the limit switch.....

reconnected, closed the door, flipped the switch and the control blinked green, meaning all is well.

switched the tstat to on, increased the temp, and the baby kicked on perfect. Purrred like a kitten.

I did a small jig

Woo Hoo.

Funny, where I was sitting on the floor last night looking up at the limit switch, I did not notice the switch connection loose. Tonight, I noticed it right off.....Helps if the seed is planted.....
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Old 09-29-2008, 10:54 PM   #25
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Awesome

Glad it was an easy fix. The last furn I installed had a bad board, and was intermittent. Talk about a PITA.

Enjoy your new furnace this winter !
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Old 09-30-2008, 07:13 AM   #26
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Got the woodstove ducting done last night, just need to finish the tstat wiring for that.

Got the 1st delivery of firewood this am. I may actually be prepared this winter.

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