Furnace cycling on and off


  #1  
Old 10-23-13, 12:40 PM
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Furnace cycling on and off

Here's my problem:

1. I have a 1993 horizontally hung Amana furnace
2. I turn the thermostat up, the induce fan blows, the ignitor glows red, and then the gas burners turn on. Everything is good until about 30 seconds in the burners shut off.
3. The main blower will turn on and continue to run even though the burners are out.
4. This cycle will continue to repeat itself indefinitely.

So far, I have tried a few things.
1. Changed the air filter and vacuumed all the vents out - I have been doing quite a bit of construction as it is an older home and there has been drywall dust and sawdust a flying!
2. I looked at the thermostat and the coil/ and adjusted the cycles on the thermostat to be longer...
3. I have NOT attempted to clean the heat sensor, I have read that could possibly be the problem. Not sure how to access it, but will give it a try.

Was wondering if there is anything else I should look for?
 
  #2  
Old 10-23-13, 12:46 PM
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Welcome to the forums.

After 30 seconds the burner shuts off and the blower starts. Does the blower shut off after so many seconds/minutes ?

Or does the blower continue to run and the burner cycles on and off ?

Can you post the model number of the Amana furnace.
 
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Old 10-23-13, 01:22 PM
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The symptoms you describe of the blower running constantly and the burners cycling on and off are characteristic of a high temperature limit switch that's opening.

Are there diagnostic lights on the ignition control circuit board? if so, what are they doing?

Use a multimeter to see if the limit switch is indeed opening and shutting off the burner and report that here.


If it is the limit switch, very likely something is plugging up the air that should be passing through the furnace and stripping away the heat produced by the burners.

In addition to what you have done, check the fan wheel to see if it's plugged with dust or dirt. If you have air conditioning, the air conditioning coile is probably above the fan and it can be plugged with dust and dirt ----check those items as well and let us know what you find.
 
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Old 10-23-13, 01:26 PM
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Exact sequence is
1. Inducer fan runs for 10 seconds
2. Burners Ignite and run for 10 second then go out
3. Main blower turns on and blows
4. Inducer goes on after about 30 seconds
5. Burners Ignite and run for 10 more seconds
6. Main blower continues to run
7. Sequence repeats again
8. Blowers turn off for a short time. about 5 seconds after 3 or 4 cycles

Model number GSI070D30A

Update: I took a little piece of fine sand paper to the flame sensor; however, that did not improve the situation.
 
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Old 10-23-13, 01:31 PM
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1. No blinking red lights on the board.
2. The main blower is brand new as of this time last year.
3. The house does have an Amana air conditioner, I'm not sure how or where to access the air conditioner coil? I will dig around though and get back to you.
4. I will also find my multimeter and see if I can find the limit switch...?
 
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Old 10-23-13, 01:34 PM
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Usually an overheating furnace wouldn't cycle the burners on for only ten seconds. But you need to use a multimeter to check to see if the limit switch is indeed shutting off the burners. That's still the mostl likely cause of the problem you describe, and the easiest to eliminate if the limit switch is staying closed and not opening.


If that's NOT happening, then we go on to plan B. But check the most likely cause of the problem first.

Can you identify the limit switch?
 
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Old 10-23-13, 04:28 PM
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[IMG] [/IMG]

Not sure if I can correctly identify which limit switch I'm looking for?

Also, I don't seem to see anyway of accessing the coil from the A/C.
 
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Old 10-24-13, 10:50 AM
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I circled the limit switch you are looking for. It is reddish in color.
 
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Old 10-24-13, 01:24 PM
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Tested the limit switch with the multimeter.
1. When the inducer fan starts up, the limit switch is open and there is no reading on the mulitmeter. Should the limit switch be open when the furnace is off?
2. Once the furnace ignites the multimeter reads that it is closed, though the signal kinda of jumps back and forth between open and close? Could the limit switch be jumping back and forth like that?

Suggestions?
 
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Old 10-24-13, 01:39 PM
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At room temperature the limit switch should show continuity. Make sure you pull the two wires off when checking for continuity. If the reading is 0 it shows continuity.

When the limit switch closes when the inducer fan causes it to do so the meter reading should be 0 across the terminals.

When the furnace is running you can test voltage on each side of the limit switch by placing one lead on the terminal and the other to ground. You should get a reading of 24VAC on each side.
 
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Old 10-26-13, 09:49 AM
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At 200 olms - the limit switch does not read 0. It should, correct?

Next step would be to replace it and see if that was the problem?

Do local shops carry these, or is this something I should order offline?
 
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Old 10-26-13, 12:28 PM
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Yes, the switch should read 0 or slightly above. The best way to determine what continuity is with your particular meter is to touch the probes together and see what reading you get. That reading should be the same when you test a component for continuity. For example, if you touch your meter leads together and you get a reading of .1 then that would be what you would expect for continuity readings. Yes, I would replace the limit switch. Your best bet is to purchase it on the internet. Get the part number off of the limit switch itself and get an exact match. If you need assistance in locating one just give me the part number. You can remove the limit switch from the furnace and tap on the "disc" with a screwdriver handle or knife blade to see if it will reset the switch. But, even if it does reset you will need to replace it to prevent future problems. I believe your limit switch is part number 10250801 but you will need to verify it before purchasing it.
 
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Old 10-27-13, 07:43 AM
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Yeah, it doesn't read the same as when the two leads are touched together. And yup, that's the part. Looks like I can get one off ebay for 15 bucks. Thanks again! Hope this fixes it.
 
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Old 11-02-13, 10:45 AM
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Limit switch came in the mail. Put it in and it started up beautifully and ran for about 3-4 minutes. It took the temperature up to where I had it on the thermostat and then shut off. When it attempted to start back up again it reverted back to it's old habits with the burners cycling on and off every 2 or 3". I opened up all the panels for the furnace to see if it was dirty or clogged, including by the a/c coil but didn't find anything. Any other suggestions?
 
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Old 11-02-13, 12:35 PM
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Your limit switch probably had been tripped too may times and failed. Replacing it did not correct the underlying problem. Continuous tripping of the limit switch usually is an indicator of inadequate air flow. Are all of the supply vents open and the return air grilles unrestricted and free flowing. Are you sure all of the air filters are clean? Is the blower producing as much air flow as it always has? Some systems have air filters located at the return air grilles. Also, sometimes the evaporator coil is clogged even though you can't tell by looking. Are you able to see the inside of the coil as well as just the outside?
 
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Old 11-03-13, 07:37 AM
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I've double checked all the returns and vacummed out all the duct work. Everything is open and freely flowing. I rechecked the a/c coil and if appears pretty clean. Couldn't wipe any dirt or anything off it.

Could something be wrong with my thermostat? I turned the furnace back on today and it has been running for a solid 30 minutes bringing temp up from 46 to 70. Have it set at 80... I think the cycling on/off problem only occurs now once the furnace kicks off after reaching the set temp...
 
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Old 11-03-13, 08:33 AM
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Difficult to say if it is a thermostat issue but if the furnace ran long enough to bring the temperature up 24 degrees in 30 minutes it points to an issue other than the furnace. After it reached the target temperature today did it cycle again as it was doing before? As far as the coil the problem is not surface dust that can be wiped off; it is the dust and debris that gets between the fins of the coil and hardens to where air can't flow through it. What type of air filters do you use? A lot of people use filters that are too thick and restrict the air flow too much and cause problems.
 
 

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