Furnace Not Blowing Hot Air - Explained | Repair and Replace

[@stephenbraden6239]

Thanks buddy

[@AmreSupply]

You're welcome!

[@Guadsquad1]

Hello! Is it ok to replace the limit switch from a L165-60F to a L165-40F? I am having troubles finding the OE temp

[@AmreSupply]

Thanks for watching. It is not recommended to install a switch with a different rating as this can affect how the furnace operates. There are some cases where substitutions are made however that is not something we can recommend from here. In your example the original switch would cut out and disconnect the circuit at the high temp of 165°F. It will wait for the temperature to drop 60°F before power is connected to the circuit again. The L165-40F means that it will be cutting in at a higher temperature, & it will not wait as long to cut in again.

[@chr3389]

Thank you is working

[@AmreSupply]

You're welcome Cristhiam, we're glad the video helped you out!

[@amineb5478]

Hi, I tested the limit switch with a multimeter and it shows 0.0 but when I tested the pressure switch no reaction on the multimeter??? The two other switches that have a reset also show 0.0. furnace still not heating? What do you think?

[@AmreSupply]

Hi Erminio, thank you for watching. A normally closed or NC switch will be normally closed (and will have continuity) at room temperature. Continuity means there is a continuous electrical path in the switch, and is any resistance value over 0. A switch is just a gate for the electricity to flow throw, which means it will have a very low resistance between 0 and 1 ohm. If the switch does not have continuity, then it will show a blank screen, - - - - - or even OL (Open loop). That is an open circuit. Keep in mind some switches are normally open NO at room temperature and pressure. You might see NO and NC terminals on the switch which will show different readings. Testing between NO and the C (common) terminals shouldn't have continuity, where testing between NC and C terminals will show continuity on a healthy switch.

[@amineb5478]

@@AmreSupply well the others I tested I heard a beep then it shows 0.0 but when I tested it no beep and no reaction on the reader it stayed as is

[@AmreSupply]

@@amineb5478 Beep and a resistance reading of 0 means there is continuity. For a switch that has C and NC terminals this means the switch is good. No beep and no change means there is no continuity. For a switch with C and NC terminals, then that switch is faulty. A switch with C and NO terminals, no beep and no continuity means the switch is good.

[@AmreSupply]

@@amineb5478 As well we have created a video on multimeters and electricity. Its a good one to watch as a refresher, and it is also animated with good visuals. Its a helpful video overall kzbin.info/www/bejne/qJDQmpqZqcaSf9U

[@CoryBry86]

Hello, I’m up late watching videos because I just changed our air filter, but the house won’t heat up. I’m getting cold air, and it’s holding at 66 degrees. It’s wintertime.

[@AmreSupply]

Thanks for watching. Did you check the thermostat fan settings? It should be set to heat and the fan should be on AUTO. Observe the startup sequence, do the flames ignite or is the furnace not igniting properly? If the flames are not igniting then it could be a faulty ignitor or flame sensor.

[@CoryBry86]

@ thank you for the reply. I had to reset the furnace. Also my inducer motor is making a loud noise do you think it needs to be changed soon?

[@kevinknuth77]

our shop heater doesn't put out much heat , is there a way to increase the gas flow. heat exchanger only reaches 80deg

[@AmreSupply]

Hi Kevin, thank you for watching. Adjusting the gas pressure can be done in some gas valves but requires special tools and knowledge. It would be best handled by a technician.

[@squidusn71]

Here's my issue. I set my thermostat to desired setting of 75 degrees(heat and auto for the fan). Ones the house heats up to 75, the thermostat shuts off the furnace. When the thermostat calls for heat again it blow cold air. So, I turn off the power switch for the furnace to reset it, thermostat is still set at 75. After switching power to on, I can see that the igniter glows, but there's no flame. I put a new flame sensor, so that's good as well. Could my limit switch be bad even though the igniter os working?

[@AmreSupply]

Thanks for watching. To work the flame sensor has to be positioned inside of the flame. It also needs a path to ground to complete the circuit through the flame, and the burner. If the burner is very dirty it can prevent the flame sensor from having a path to ground. Try cleaning the burners first. Also check to see if your furnace gives you any codes as this will likely tell you if its a "no flame sensed" or a "open limit switch" this can help you determine your next steps.

[@squidusn71]

@@AmreSupply the code is a steady blink which is normal according to the label on the panel. I have the trane xr80.

[@AmreSupply]

@@squidusn71 Reading your message again, if you do get heat some of the time then you've verified that your gas valve is working and the system is able to heat up. It could still be an issue with the limit switch.

[@squidusn71]

@@AmreSupply ok thanks for the response again. So I got heat throughout the day but it started blowing cold air again latein the evening. The same thing keeps happening, however, I was able to see a code this time(2 fast blinking lights). According to the code label, it reads external lockout(retries or recycle exceeded). Is that the limit switch? I did order the limit switch this afternoon while watching your vedio on it. I really appreciate the help.

[@squidusn71]

@@AmreSupply by the way, all this started after I changed the filter.

[@iSmiley.]

XR90 -Initially shut furnace off @ thermostat for 2-3 hours. Tried again and it was working fine again -2 days later, same symptoms again (no heat) -reset at breaker -calls for heat (fast consistent flashing). Seems like everything is going great -suddenly a suction type whistle like sound -reverts back to slow consistent flashing (no call for heat) -Keeps trying over and over again to call for heat, but fails - no fault codes at all Sound like a limit switch?

[@AmreSupply]

Thanks for watching. From what you described the furnace isn't getting far into the sequence. When it calls for heat, first the draft inducer pulls fresh air into the burners. The pressure switches check the pressure to ensure airflow. Then the igniter heats up, the gas releases and the burners ignite. Then the flame sensor checks the flames. From the sounds of it you likely have a issue with the pressure switch or bad airflow: This sequence of operation is mentioned here: kzbin.info/www/bejne/mGHWcnqqYpahn7c as well the full "How it Works" is shown here: kzbin.info/www/bejne/qoevpX2tnt1glZo Hope this helps!

[@iSmiley.]

@@AmreSupply Was a faulty GOOGLE NEST thermostat mimicking all that. HVAC guy had to disconnect the fan to somehow power it as the RC connection wasn't enough. Hope that made sense. No "fan only" now, but that's ok, I don't use it any way. Be forewarned; sometimes it's the NOT SO smart thermostat!

[@bamboozleman6653]

My thermostat continues to blow cold air when set on "on" and when its on "auto" it doesn't blow at all.

[@AmreSupply]

Thanks for watching. If the furnace heats normally when in the "ON" setting, but doesn't heat at all during "AUTO" then It could be an issue with one of the wires or wire connections between the thermostat and furnace. Alternatively it could be a faulty thermostat.

[@dedameda199]

if the electric air heater Carrier blows but does not heat

[@AmreSupply]

Thanks for watching. Many of the tips in this video still apply to electric heaters including the thermostat settings and the limit switch.

[@kikilari]

Wait...so the fan should be set on 'Auto' or 'On' to get heat?

[@AmreSupply]

Thanks for watching. On means that the fan will be constantly on and will run 100% of the time. Auto means that the fan will only run when heat is needed.

[@debbieluv2717]

Limit switch

[@AmreSupply]

Thanks for watching.

[@rhondarockwell9489]

Ok mind its doing just that just u said amen. Ok SF-25 FQ now my thermostat run on both Coleman mach 15 ac rv can u tell me with is the right thermostat i need so i get the right i going to buy new thermostat and sail switch today from Amazon please help it got ALXCel on temperatures u know what i mean😮

[@AmreSupply]

Thanks for watching. RV furnaces are outside of the scope of our videos and our information. There are other videos and forums that can provide more specific information on this.

[@stephenbraden6239]

Electric furnace in mobile home is only blowing cold air instead of heat. It has been working fine until 4 days ago. Any help would greatly be appreciated.

[@AmreSupply]

Thanks for watching. Though your question is outside of the direct scope of this video there are still some things you can check. With an electric furnace, the first thing to check is if the heating element is still good. We don't have a specific video on electric furnaces but the steps will be the same as testing a heating element for an oven: kzbin.info/www/bejne/d3PSoZhtq9Fof7s If the heating element is good then it could be a faulty limit switch or an issue with the control board.

[@joshuarobinson9821]

Well my family woke up to it being cold so we thought the thermostat battery's was bad but when we switches the furnace on, it blows cold air and then shuts off. We think it might be the igniter

[@AmreSupply]

Hi Joshua, thank you for watching. In most models if the igniter is faulty then the furnace will shut off before the blower fan runs. Best to check the furnace filter as a clogged filter will prevent good airflow and can trip the limit switch. As well a faulty limit switch can also cause the furnace to blow cold air then shut off.

[@joshuarobinson9821]

Hi thank you for the help we checked the switches and it ended up that the pressure switch was seized up

[@AmreSupply]

@@joshuarobinson9821 Thanks for the update, we're glad you were able to narrow it down!

[@ClarkHuman]

There's no way to adjust the limit switch like you can on a Honeywell.

[@AmreSupply]

Hi Clark thank you for watching. You can get adjustable limit switches: www.amresupply.com/search?q=limit+switch+adjustable but these are meant to adjust to a specific temperature that the furnace is rated for. Generally these are used to match only.