Lennox furnace temperature control

I have a home furnace with a lennox control. It's about 30 years old.
The problem is that, when the room temperature is cold, like 55 degrees F, and the control is set to 70 degrees F, the furnace only runs for about a minute, shuts off for maybe 3 to 6 minutes, then runs for another 1 minute. I'd rather the furnace ran until the temperature reached 70, then turned off and turned on again when the temperature dropped to, say 67.
There seems to be a way of setting things when I take the cover off the control. But how do I use it? Is it possible to get the controller to work as I like?
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Sounds like a thermostat issue. Is the thermostat the same age as the furnace? It could also be the location of the thermostat. If it is in line with a vent, it may be prematurely warming.
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Are you sure it's the entire furnace shutting off, ie the burner and the blower? I would bet that what's really going on is that the burner remains lit, but the blower is what's going on and off. That is perfectly normal under those conditions. My furnace does it too. Here's what's happening:
The house is very cold, 55. You turn up the heat to 70. The thermostat calls for heat, the burner lights. When the temp inside the furnace plenum gets hot enough, which is a couple mins, it closes a temperature switch that turns the blower on. Normally, the blower would then continue to run until the burner shuts off. The blower continues to run, recovering the remaining heat, until the temp decreases again, at which point the blower turns off after a couple mins. However, you have very cold incoming air. So cold that when the blower starts, the air flow drops the temp in the plenum below the shutoff temp for the blower. The blower stops and then the air begins to heat again, repeating the cycle. So, you get the blower running for a min or two, stopping, repeating. That continues until the air in the house is warm enough so that it won't drop below the blower turn off temp anymore.
A simple solution to this is to just turn the blower to run coninuously via the fan switch on the thermostat. You do that whenever the house is unusually cold and then turn it off again when it reaches a more moderate temp, eg 60.
And if the furnace is 30 years old, suggest you look into replacing it. That furnace was designed to 80% eff, at best, when it was new. Today it may be running at 75%. You can get a 95%eff furnace at a reasonable price and there are substantial rebates available from loca utilities, state, etc. The best deal was last year when you had that, plus a 30% Fed tax credit too.
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On Fri, 14 Jan 2011 10:56:29 -0800 (PST), snipped-for-privacy@optonline.net wrote:

He never said if he had gas or oil heat. I finally found the manual for my 31-year old oil furnace and it was 80% efficient. I don't know what it is now, but I do know that the woman down the street replaced an identical furnace to mine with a Bryant, and it is labeled 81.5 percent. The highest oil efficiency goes is about 84 percent unless one gets some special kind which I gather is very expensive and not popular.

Yes, I'm sorry to say I missed that, (but in my case it's not as bad as it sounds to miss it). Still my friend tells me that the recent tax bill included a 10% fed tax credit for 2011 (or longer?) in place of the 30%. I haven't heard this anywhere else, but she's rarely wrong. Anyone know?
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On 1/14/2011 11:10 AM, Monty wrote:

On a furnace that old, I'm assuming it's natural gas, the fan limit switch can get wonky. Take a look at the web pages:
http://www.inspectapedia.com/heat/FanLimitSwitch.htm
http://www.inspectapedia.com/heat/Fan_Limit_Switch_Test_Procedure.htm
I replaced many of them.
TDD
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