Evcon DGAT075BDF Furnace not working

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Evcon DGAT075BDF Furnace not working

Postby markmc59 » Thu Nov 11, 2010 8:53 pm

Hey guys, great site. I have been working on my furnace for a day or two and need some help.

I have an Evcon DGAT075BDF that is in need of help. The AC worked fine but when I went to turn the heater on...no dice. I was getting 3 flashes (Combustion air switch failed to close). I replaced the combustion air switch with a toggle switch to override the switch to test it. I left the "bad" combustion air switch attached to the 2 hoses coming from the combustion blower motor and the other going to the furnace.

Now the furnace will attempt to ignite the 3 times but fails each time. So I started checking the switches and solenoids. I metered the brown wires at the gas valve to see if I was getting the 24v. The ignitor will glow then I get 26.x volts at the gas valve. The furnace actually attempts to light with ~1 sec of flame and then the voltage at the solenoids drops. It drops as if the control board told it to drop due to a bad switch.

I then ohm'd the upper limit switch and the lower limit switch. they are both closed when the furnace voltage is off.

Does anyone have suggestions? I have a new combustion air switch coming my way but that in itself will not fix the problem. Is the control board bad? Does it require a vacuum/pressure source from the hoses?

Any help would be greatly appreciated. I can meter anything y'all ask so that there are objective measurements.

Thanks
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Fri Nov 12, 2010 7:46 am

Some help please.
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Fri Nov 12, 2010 10:46 pm

Well my combustion pressure switch came in. I think they may have sent the wrong one.

I ordered: 1 Coleman Furnace Air Pressure Switch 024-27666-000 -0.15.

They sent: Honeywell pressure switch (S1-32435972000). For use with models: DGAA & DGAH.

I am about ready to just call someone to fix this. Any ideas?
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Re: Evcon DGAT075BDF Furnace not working

Postby Robert » Sat Nov 13, 2010 11:35 am

Hi,

Having some health issues, let me read everything and will reply back shortly.


Thanks,
Robert
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Re: Evcon DGAT075BDF Furnace not working

Postby Robert » Sat Nov 13, 2010 11:46 am

Hi,

The gas valve should have 24vac and be open for about 6 seconds, before it shuts down IF flame not sensed at burner.

Check burner tube and burner orifice/spud behind gas valve for blockages (spider-web-bug).

IF you have a remote flame sensor, clean it carefully with steel wool.


The pressure switch closes once it reaches set water column pressure.

Be sure combustion air pipe is not clogged or separated/leaking, combustion motor and wheel are clean and running strong and tubes are not clogged, kinked or loose.


Be sure ignitor is getting full 120vac for ignition cycle.


You did receive the wrong switch, will need to return it.

Correct switch is 024-27666-001 (new p/n).



Thanks,
Robert
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Sun Nov 14, 2010 2:46 pm

I do have a "sensor rod" as the diagram calls it. So I will clean that if I can get it out. Where exactly is the combustion air pipe? Would you happen to know the best way to remove the gas valve so that I can reach all the "internal" things?

Thanks!

PS: I hope your health issues get resolved.
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Sun Nov 14, 2010 3:24 pm

Also, should I feel blowing or suction from the tube coming from the combustion motor?

Do I need to open it up to check the combustion wheel?

I have hope!
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Sun Nov 14, 2010 3:28 pm

Here is what I'm working with:

Image

Image
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Sun Nov 14, 2010 4:53 pm

Ok. I cleaned the orifice and sensor rod. The furnace has a flame for ~2 seconds and then drops out. I do not know what the combustion air pipe is so that has not been checked. Also I have the air switch out completely since I am using a toggle switch to skip it right now, that means the 2 tubings are open to ambient air.

Any ideas what would make the burner fire for 2 seconds and then stop?

Thanks
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Re: Evcon DGAT075BDF Furnace not working

Postby Robert » Sun Nov 14, 2010 8:19 pm

Bad sensor rod possibly. Sensor rod not positioned correctly.The combustion Air Pipe is pie connecting to top of booster motor assembly.

To bypass pressure switch for test run for a short while only, just jumper the switch terminals.

That is a safety switch however and should not be bypassed long or more than once.


Health issues will be here til the end, just have to live with them.


Thanks,
Robert
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Re: Evcon DGAT075BDF Furnace not working

Postby markmc59 » Mon Nov 15, 2010 7:46 pm

Well, I had someone come by because the weather is getting cold here. It looks like the combustion motor was bad. Thanks guys!
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Re: Evcon DGAT075BDF Furnace not working

Postby Robert » Mon Nov 15, 2010 11:22 pm

You're very welcome, happy to help.


Thanks,
Robert
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