Furnace turning on and off

Hello, My furnace recently went out (on the coldest day in Chicago nonetheless). It turns out that the intermittent pilot control (Johnson Controls G779) failed from being overheated. We could see warping around the circuit board, but it also turned out that the air filter was also plugged.
After installing a new pilot control and air filter, I am very worried that the heater may still be overheating. The heater has been on for several hours to heat the house up from a warm 37 degrees. The burners go on for 4-5 mintutes, and then shut off. After 1-2 mintutes they are reignited. The fan stays on for the whole time. This process repeats itself while the thermostat is still set.
Is this normal for an old gas furnace that has been on for a while? The technician said that if it displayed behavior like this the A-coil may be plugged. Is this likely? Any tips would be most appreciated. Thank you.
-Charles
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snipped-for-privacy@alumni.princeton.edu wrote:

(Johnson
worried
burners
are
When you say the fan stays "on", I am assuming you do not have your thermostat set at "fan on", in this case no, I don't think it's normal. The burners are suppose to stay on until the thermostat is satisfied. Something else is not working right. You should call someone to have a look at it.
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The fan stays on when the thermostat is set to "ON" and the desired temperature has not been reached. If I turn the thermostat off, everything turns off. My concern is if the burners should be cycling like they do (on 5 minutes, off 1 minute) when the unit is "ON".
Mikepier wrote:

filter
for
repeats
normal.
a
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wrote:

As other poster said sounds like a part changer.
Assuming your t-stat is not set for fan on, then the burner should come on stay on and run until t-stat is satisfied. Your description is that the burner is coming on then off fan stay on until it cools down. Fans usually stay on to remove all of the heat from the exchanger. It sounds to me like you do have another issue with the heater. Have you changed your filters recently? Start there for sure. If that fails to correct the problem and I would be very surprised if it did... (sorry) You need another service call to clean the unit. Which with gas should be done every year anyway. At least I did when I had gas heat. Maybe I am just more paranoid about gas than you are.
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On 15 Dec 2004 21:23:52 -0800, snipped-for-privacy@alumni.princeton.edu wrote:

Your problem is you have found a parts changer. Fixed the part, left the problem. If it overheated, you need to find out why. If you have a gas leak in your home and the house burns down, you have to rebuild the house, right? Do you just leave the gas leak for the house to burn down again? Bubba
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Question? Was this the way your furnace was working before the part was changed, only worse because of the clogged filter? Did your repair man take a temperature rise from the return air to supply, or look at the coil? I would bet that your problem is in the fan/limit located directly above the burners, probably a honywell. You need a competant hvac tech, not someone that says it probably is something, after he already charged you to repair the unit.
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It is not normal and is possibly due to dirt on the A-coil restricting the airflow. This would cause overheating which would cause the safety limit switch to cut off the burners. When it cools down, the safety switch would then allow the burners to come on again and repeat the cycle. You definitely need the problem diagnosed immediately and not continue to run the furnace. Don Young

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