Question about Heating & Cooling
Posted by Anonymous on
Sounds like it needs a good maintenance. What did tech do to fix it?
Posted on Jul 23, 2017
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Posted on Jan 02, 2017
SOURCE: Limit Switch
It is rare that a limit switch goes bad. It is a safety control. If it is shutting off your furnace there is a problem that it is protecting you from.
If the limit switch is shutting the unit down your furnace is overheating. Check the filters. Check for any obstruction in the blower assembly. Check to see if you can raise the blower speed. Make sure all registers are open in the house. Your evaporator coil could be obstructed if you do not take good care of your filters.
Posted on Mar 08, 2009
Today’s furnaces are controlled by a computer which constantly monitors for problems. When it detects a problem it will shut off the burners. Depending on the problem and the specific furnace it will either “lock out” the furnace or cycle it through a purge (to rid it of un-burned gas and excess heat) and then attempt to re-start it. If the problem continues to occur then it will “lock out”. Depending on the problem and the furnace it may again attempt a re-start after several hours. In any case if the problem was not detected/caused by a sensor which requires a manual re-set, when the power to the computer is interrupted or the call for heat is interrupted the computer is reset and it will again attempt to re-start the furnace. The most common problems are:
· Low or lack of flame sense. Different furnaces use different methods to detect a flame – often these “flame sensors” become dirty and have to be cleaned (usually with sandpaper or steel wool).
· Bad igniter. (Doesn’t light at all).
· Clogged combustion air intake or exhaust.
· Clogged condensate drain. (90+% efficient furnaces).
This is not a complete list, only the most common!
Depending on where you live your HVAC system runs more than anything else you own (including your car). All furnace manufacturers “recommend” “regular maintenance” of your furnace. In fact, all that I am aware of state in their warranty that the warranty may be voided due to lack of “regular maintenance.” The industry has defined “regular maintenance” as yearly (in fact, some manufacturer’s warranties state yearly). Due to safety, liability, and the need for many other things to be checked, cleaned, and/or adjusted (2-page checklist where I work) to ensure safety and efficiency. Due to the large number of furnaces and the differences between them. Moreover, due to the terms of this site, I WILL NOT AND CAN NOT give you specific instructions on how to perform repairs on your furnace. I suggest that you contact a local, reputable, HVAC service company for (a tune up, preventive maintenance, general maintenance, yearly service call, general service, or whatever they call it).
While I may not have told you how to fix your furnace yourself, I have told you how to fix it. Please rate my answer.
Posted on Mar 14, 2009
If unit worked before you tryed changing t-stat then its possible the t-stat wires are shorting each other out.take t-stat back off cut back wires a good 6 to 10 inches or if you dont have that much wire to play with just cut back as far as you can and make sure there is no bare wire touching each other ,then just to test unit to make sure its working ok twist yell.,red,green together this should bring both units on and should blow cold.if this works up to this point on the new stat read directions closely there might be a jumper wire in the stat that needs connected usually from y1 to w1 you would install a jumper wire .see if this helps if not write back i have 1 other solution.i hope this helps
Posted on Sep 15, 2009
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!!
Posted on Nov 20, 2009
Your unit has a diagnostic light on the circuit board. You need to look thru a small viewing port to see it. Once you count the number of b links, remove the lower panel and look at the wiring diagram for an error code chart. Then read the following to give you some ideas what to do.
On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.
What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).
Posted on Dec 01, 2009
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