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Old 05-02-2012, 06:57 PM   #16
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No Heat ?


ha ha...okay we are a bit new to using the volt meter so maybe he was testing wrong. I will have him read this to see if he did it this way...he asked me to order today and I have those items sitting in the "cart" and my argument was going to be its not going to make a difference if we wait another day since it would fall on the weekend regardless.

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Old 05-02-2012, 07:21 PM   #17
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No Heat ?


..Turn furnace on.. if you measure 24 volts across the limit its open ..wire still on limit of course... or pull wires off and ohm limit out...
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Old 05-02-2012, 08:40 PM   #18
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No Heat ?


You also mentioned flame roll out switches. Find every one of them around your burner compartment and check if they have a reset button that needs to be pushed back in. If that turns out to be so, let us know as it takes the diagnostic's in a different direction.
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Old 05-03-2012, 08:36 PM   #19
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No Heat ?


OK...now we believe we tested it correctly I am going to show you exactly what we did and if it is wrong tell us what or how to correctly do it.


What we tested came back as closed...Are these the flame rollout switches? We only have 2 and both are not out. Here is the photo...


And here is just a general photo of inside the top portion of the furnace


We followed the lines from the limit circuit which lead to the safety but we couldn't follow beyond that because it went up the back. The board is clean behind as well...any other ideas?

Thanks again and sorry we didn't get back sooner last night was a bit hectic.
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Old 05-03-2012, 08:53 PM   #20
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No Heat ?


The one that's being tested is a flame rollout switch. You said you have two, very common. That button in the middle of the switch can be pushed in to reset the switch, if it trips.

I test continuity by removing the two wires from the switch and checking to each prong, across the switch with the meter on the ohms setting which is what I believe it's on in your pic. When you check for voltage you check from one prong to ground with the wires on the switch, like in the pic. You can use one lead to the prong and one lead touching the metal cabinet of the furnace. That should show what is known as potential voltage. If there is 24-ish volts in the line than potentially if given a path the 24 volts will go to ground, the cabinet. The meter will read this potential. Check from one prong of the switch to the cabinet and then the other. If both prongs show potential than the switch is closed as from both points there's electrical potential, not just one. Also means there's continuity, switch closed.

Don't forget to use a/c voltage and not ohms on the meter settings if you are doing it this way.

You're going to have to trace that wire back and find the other limit switch. If these ones are showing continuity than most likely the other one(s) would be the problem.
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Last edited by Doc Holliday; 05-03-2012 at 08:57 PM.
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Old 05-03-2012, 08:56 PM   #21
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You have three flame rollout switches, the one being tested on the bulkhead in the pic and two on the burners. Again, if all of those are closed than you're going to need to find the other limit switch(es).

Btw, you can only check for voltage on these switches if there's power to the furnace. If you have a door switch then you need to tape the door switch down and turn the heater on.

Checking for continuity, no voltage required. Checking for voltage, well, voltage required.
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Old 05-04-2012, 12:10 PM   #22
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Ok - left it on last night just so the whole house fan could move the air around in the house. Went down this morning and it was off - the intake fan and whole house fan were off. I thought this is different, so I turned up the thermostat to call for heat and sat down next to the furnace and looked through the peep hole. The intake fan came on and then the whole house fan, then then I heard a click and the ignitor illuminated and the flame came on.. I thought great... we fixed it. but about 2 seconds later the flame went out. I continued to watch and the same thing happened two more times. I then turned the stat down cancelled the call for heat and the intake and house fans eventually shut off. During the diagnostics last night we must have done something atleast partially right. Anyone know why the flame wont stay on. Sounding like a safety related switch???? I still have to check the other limiter switches I found two more on the whole house fan just could get to them yet.
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Old 05-04-2012, 12:25 PM   #23
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Flames sensor. In the pic of the roll out switch being tested, to the right of the switch and in the burner compartment, follow that single blue wire to the flame sensor. Pull the wire off of the sensor, remove the sensor (usually one 1/4" screw) and scrub the metal rod with a scotchbrite scouring pad or fine sand paper.
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Old 05-04-2012, 12:33 PM   #24
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Just to the right of the roll out switch on the right side, the single blue wire is running to the flame sensor, attaching from the bottom.. The white porcelain base, that's the flame sensor.
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Old 05-04-2012, 02:24 PM   #25
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We actually already have pulled it out and cleaned it off with some sandpaper. We pulled each of the items out that we were going to buy to get the numbers off to make sure we were getting the right part and cleaned in the process. But, we will pull it out again and make sure we did it well. I will be excited if it is this item...since this is the one I have thought it was all along.
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Old 05-04-2012, 03:43 PM   #26
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Since you have had the ignition assembly apart, I have to ask this...Did you reassemble it properly? When the "pilot" lights is the flame sensor in the flame? In order for the electrical continuity to happen the flame sensor has to be enveloped in the flame. Also, is the connection for the flame sensor wire to the board clean? Any corrosion here can cause problems. How does the "pilot" flame look? Is it burning big and clean? I recently had one of these that needed the "pilot" orfice cleaned to get a better flame
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Old 05-05-2012, 06:27 PM   #27
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Cleaned the flame sensor really well and the first time it lasted 13 sec. and then each additional time it was only 3 sec. We also don't have a pilot it is electric ignition (like a glow plug). Cleaned all the connectors and crimped them down a little tighter to make sure there was a good connection. Hmmmmm...
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Old 05-05-2012, 06:56 PM   #28
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No Heat ?


Your Flame sensor uses the main burner flame as an electrical pathway to the closest ground. Make sure that the metal immediately adjacent to the flame sensor is also clean.

A dcma series test with the flame sensor when the burners first fire up would be what we would be testing.

I believe the terminal for the flame sensor at the board should also be putting out 80 - 90 Vac to work?

Let us know what you find.
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Old 05-06-2012, 03:31 PM   #29
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Quote:
Originally Posted by jesmoose View Post
Cleaned the flame sensor really well and the first time it lasted 13 sec. and then each additional time it was only 3 sec. We also don't have a pilot it is electric ignition (like a glow plug). Cleaned all the connectors and crimped them down a little tighter to make sure there was a good connection. Hmmmmm...
Unit needs a good ground wire connection. The control board as well. Might want to check that.

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