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Heil DC90 gas furnace need to find reset or limit switch

I have a heat exchanger problem and no money for repairs until Jan. Short term solution is to hit rest(limit) switch. Cannot locate switch.

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SOURCE: i have an older model heil quaker natural gas

Test to make sure the limit switch is still working prior to the rewire. Use an Ohm meter and test for continuity. If good, use some good quality 14 or 12 guage wire to rewire. If the unit has an in-line fuse, you will need to replace that as well.

Posted on Mar 27, 2010

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SOURCE: I have a heil dc90 furnace wondering what the

lpg is 12 to 14 inches wc nat gas is 4 inches wc ,

Posted on Feb 02, 2011

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The heat exchanger must be free of cracks and holes due to the potential of carbon monoxide leakage. You can probably make a short term repair with sheet metal and high heat furnace refractory cement, but that is a quick fix only.
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This indicates a open limit switch on the furnace, the heat exchanger is getting to hot therefore the limit switch is opening and not allowing the furnace to work properly. Did the techinician check the limit switch on the unit?

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PGB030075-1 Led light is blinking 4 quick blinks. blows out cold air. What does this mean?

4 blinks indicates a failure at the high limit switch. This switch is usually located on the heat exchanger face plate and has two wires going to it. Usually it fails because the furnace has over heated. The most common reasons are a plugged filter or coil that is limiting the airflow over the heat exchanger. Turn off the power to the furnace, replace the filter, clean any coils in the plenum and verify that all the vents in the home are open. Then turn the power back on and see if it is fixed. :)
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I have a Lennox Whisper Heat that when a call for heat comes, the pilot lights as it should, then after about 30 seconds the blower fan comes on, then its about another minute before the burners light....

Yes it should go in this sequence, first exhaust fan, after establishing air flow you get a pilot, after signal from pilot is established you get main burners, then they have to reach a set temperature on the high limit and then the blower comes in. Now you have several over heat safety sensors one of them could be tripped check by powering the furnace down and see if they have a reset button on them, some do some do not. If not it should be the sensors closest to the heat exchanger and blower assembly use a volt ohm meter and check them should be normally open until temp is established then closed. This is easier done than it is to describe, now locate the high limit switch and bulb and see if it is open across the contacts it should be until it hits temp then it closes to start the blower. Hope this helps instead of confusing the hell out of you. Take your time locate the items then test.

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Need make and model number of unit. But sounds like a limit switch. Check filters and pull and clean limit. It is located above burner. Small square plate with two wires coming off it. Rus

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It sounds to me that your air flow is restricted somewhere. The first thing to check is your air filter. If that gets real dirty your restricted air flow will cause the hi-limit(hi temperature limit switch) in your heat exchanger compartment to over heat and open up your gas valve electrical circuit,thus, shutting off the gas to your burners. After the hi-limit switch cools down the furnace will go back to heating again then it will overheat again(you get the picture?) If it keeps cycling on and off like that the house will never get warm if it is cold outside. If your air filter is reasonably clean(you should be able to see light thru it easily) then the secondary heat exchanger could also be dirty, this is located above the indoor fan housing, you would need to pull the indoor blower assembly out of the furnace and look up above. The secondary heat exchanger looks similar to a radiator will fins. You can use a medium stiff plastic brush to brush the dirt,hair, whatever off of it. Another problem spot would be the cooling evaporator coil (if you have central airconditioning) located most likely above the furnace in the plenum(if your furnace is in a basement). This usually is difficult to access if an access cover wasn't installed when the airconditioning was installed. I would recommend an experience service tech to clean it for you. Also make sure all you supply air registers and return air registers are open . These are the things I would check first. Good luck!!

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Could the fan motor be heating up and shutting down on thermal overload? How long of a duration does it stay off before it starts again? Typically there is a bi-metal switch that rests on the heat exchanger and starts and stops the fan motor. If it is bad or not resting against the exchanger it will not operate as it should. Check the location of the switch. If it is touching but still cycling, test your switch with a multimeter set on Ohms. Let the heater run, jump the two wires you pulled off the switch (they are 120 volts so be careful) and watch your multimeter to see when the switch opens and closes. If it cycles as it has been, you have a bad motor. If the switch closes as the heat exchanger gets hot and stays hot as long as the heater is running, the switch is good.

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