Janitrol constantly cycling on and off

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Old 01-10-10, 09:39 AM
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Janitrol constantly cycling on and off

I just bought a home and the Janitrol furnace (8 years old) is cycling on and off continuously. I had a HVAC tech out and he said I probably had a cracked HE. This was causing the furnace to cycle of the limit switch instead of the thermostat. He said I'd need a new furnace, and talked about the tax rebate and how this is an excellent time to do it. I had a second opinion out, and he did a complete heat-loss analysis of the house. He said the HE is fine, and it is easy to tell since their is no roll out. He said the intake airflow is 500 cubic feet too low, and the duct work into the furnace (9" metal pipe to 12" flex pipe) needs to be redone. He wants to add two return air mix box plenums, each taking two of the return pipes before connecting to the furnace, and a fifth 9" intake duct to the room above the furnace. He said this will solve the cycling problem. It's an $1800 estimate for this job. Does this sound like a legitamate analysis and solution?

The house is 2700 square feet, and the furnace is 90% efficient and 120,000 btu's.
 
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Old 01-10-10, 11:13 AM
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to see if your return is limited remove the fan access panel and then lean it up against the fan section so it covers 1/2 of the opening ..this will give the fan ,ore air to move the heat off the heat ex...see if the fan stays on.do you see as you look into the fan control area above the fan section a silver covered HONEYWELL control with a red button on it and a silver dial within ? something is cycling the fan in the heat mode if no HW control a klixon might be weak that closes after the HX gets hot and is cycling the fan...how about a model number of that furnace...what type of room stat is on that unit....for now if cold in the house put the fan to ON at the stat and set the heat normally.FYI the fan during the heating cycle is controlled by one of 2 trhings older model furnaces sense the burner section heat(HW) and newer models use a timed delay off a solid state board within the furnace control section.
 
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