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Old 09-19-2012, 10:03 AM   #1
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Confusing Luxaire GM9 Problem


Hi all,

Some background. I have a Luxaire GM9 series furnace that is probably close to ten years old. It has given me endless problems, along with the more than yearly three red flash pressure switch code. I have dealt with it successfully each time.

Yesterday I hooked up a new thermostat and changed the filter in preparation for the cold months. I had the stat call for heat and the blower fan came on immediately. Not good.

Went downstairs to see what was up. Three red flashes. Common enough, only this time the inducer motor was not running, the blower fan was and there was flame burning in the box. I went through the typical needle reaming of vacuum prorts and checking hoses. Got the pressure switch to click. Still no inducer motor. I had to replace this motor 2 years ago because it was not creating enough vac, but it still ran. I kept that motor and hooked the old one up to see if it would power up. Nothing.

My cellar tends toward dampness, so wire connections were my next thought. I pulled the two plug connector off of the control board, inspected them and reseated them firmly. I checked the fuse and it is good.

After this all I have is igniter glow and a rappidly flashing red light. Did i destroy the control? Could this be a single problem all the way through?

I am planning on checking voltage at the transformer this evening.

Other than this I am totally lost.

Please help....

Thanks very much,

e1

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Old 09-19-2012, 10:37 AM   #2
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Confusing Luxaire GM9 Problem


if the main flame was "on" without the ventor motor running there is a serious safety problem..the flame should NOT be allowed to light unless the ventor motor air switch is "made" after the ventor motor has been running and has established air flow. i.e., in a closed position..therefore this leads me to believe that the air switch is stuck in the closed position..check both pressure and vacuum lines AND the switch itself to make sure they are clean and operating properly..when the switch is stuck closed it will allow the burner to light however it most likely causes other problems to occur with electronic codes etc. Personally, I would just change the pressure swtch ..it may have a defective diaphragm...also when burner running without ventor motor/air flow it will cause excess carbon monoxide and excess sooting of heat exchanger and possibly dump CO into your living space

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Old 09-19-2012, 11:00 AM   #3
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Confusing Luxaire GM9 Problem


Shut it off and restart it. If the flames come on without the inducer motor ever starting...regardless of whatever componet parts might be faulty.... the board isn't doing its job.
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Old 09-19-2012, 11:09 AM   #4
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Confusing Luxaire GM9 Problem


Thanks techpappy, I will try to get ahold of a new switch. The most confusing part for me is how the symptoms progressively changed as I tried to solve the original problem. by the time I gave up all I had was the glow of the ignitor but no fire. The "twinning error" code sent me upstairs with the white flag waving.

Do you think the switch could cause all of it??

I genuinely appreciate your quick answer and good advice.

e1
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Old 09-19-2012, 12:09 PM   #5
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Confusing Luxaire GM9 Problem


Thank you but, you are just starting by replacing the switch..you must observe operation to make sure the ventor motor runs, then the switch makes to allow main burner operation,, check switch operation by disconnecting vac hose after the burner starts..it should cause valve and flame to shut off...try sequence 3 or 4 times to make sure. As previously stated doesn't appear board is doing it's job either. Make sure all mounting screws on board are snug/tight then try operation and let us know what's happening.
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Old 09-19-2012, 01:24 PM   #6
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Confusing Luxaire GM9 Problem


Quote:
Originally Posted by techpappy View Post
Thank you but, you are just starting by replacing the switch..you must observe operation to make sure the ventor motor runs, then the switch makes to allow main burner operation,, check switch operation by disconnecting vac hose after the burner starts..it should cause valve and flame to shut off...try sequence 3 or 4 times to make sure. As previously stated doesn't appear board is doing it's job either. Make sure all mounting screws on board are snug/tight then try operation and let us know what's happening.
Understood entirely. After being let down so many times by failures of this unit I have learned to listen for order of operation. When I heard the blower kick on instantly I knew something was very wrong. When I manually ran it and saw the flame burning without the inducer motor running it sent a chill up my spine. As "how" wisely commented, something in that control should have stopped operation before that even happened.

Thank you both, I will let you know how it plays out.

e1
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Old 09-19-2012, 06:31 PM   #7
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Confusing Luxaire GM9 Problem


No local shop to get a pressure switch at, so I went downstairs with a voltmeter to figure out if something was up with the control.

Checked 4 terminals on the transformer. 120v on one side. 24v on the other

Checked the terminals where the 4 wire plug apparently supplies juice to the ignitor and the inducer motor.

1 black wire pin 120v
2nd black wire pin nothing
Yellow wire pin nothing
white wire pin nothing.

No voltage to the two pin inducer connector. Ran 120v directly to the inducer and it ran for the first time.

Am I safe to assume that the control board may be all of my problem, throwing in a new pressure switch just in case?

Any guidance would be very much appreciated.

e1

Last edited by eccentric1; 09-19-2012 at 06:51 PM. Reason: had to delete idiotic transformer question
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Old 09-19-2012, 07:08 PM   #8
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Confusing Luxaire GM9 Problem


if you still have old thermostat ..put it back in and see if the furnace will work..could be TT wired incorrectly...maybe?...however it still disturbs me that the burner came on without the ventor motor working so, that could be the board ..Can you check continuity across air switch as well to see if it is open or closed without the inducer being on..then again you said there was no power to the inducer..could be board or TT?.. I think you said you tightened all electrical ...including board mounting screws? Also you said very damp in basement..try removing board and drying out thoroughly ..then reinstall..if no go then likely new board..pretty much everything is controlled through the board...most of my experience is commercial so, would need to see wiring diagrams and service manual to be of any more assistance...checking the air switch was an easy first step
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Old 09-20-2012, 05:13 AM   #9
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Confusing Luxaire GM9 Problem


Going down a skewed path....

The control board is your problem. Don't put an unnecessary pressure switch on. If the pressure switch were stuck closed the control board should have seen that. You have not once proved that the switch was stuck closed. You have proved that the control board is bad. The thermostat is not going to change anything. It either is calling for heat through the W circuit or it is not. You NEVER should see a flame without the inducer running. The control board controls all gas heating functions once it receives a 24V signal on W (call for heat from thermostat).
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Old 09-20-2012, 03:34 PM   #10
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Confusing Luxaire GM9 Problem


Picked up a furnace control this morning and will attempt to install it tonight. I will post the good, bad or ugly tomorrow.

Thanks for all the advice to this point!

e1
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Old 09-20-2012, 08:38 PM   #11
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Confusing Luxaire GM9 Problem


Just finished installing the new circuit board control and all is working exactly how it should be. Of course this means weeks of listening for order of operation every time I hear the stat call for heat. I think I will stay up a little later than usual and read....just in case.

By the way, my local HVAC repair and installation company was extremely competitive on the control price, within eight bucks of the best price I could find online with shipping. Plus I did not have to wait a few days. I am glad I did not assume them to be overpriced.

Thanks very much again to all that helped with the diagnosis and confidence to do this.

e1
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Old 09-20-2012, 08:51 PM   #12
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Confusing Luxaire GM9 Problem


Thanks for getting back with results...good to hear of your success..congrat's!

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