Life HVAC Limit Switch Trouble Shooting?

NewChief · 03-31-2014, 09:53 AM

Okay,

I'm capable to buying and replacing the limit switch in my HVAC unit (I know that's what is wrong with it). My issue is that I don't want to just replace the thing and it get thrown again because whatever the original issue was hasn't been resolved.

What should I be looking for that might have caused it to throw in the first place? I'd recently changed the filter, so I don't think that was it. It does look like there's a lot of built up dust around the fan unit, though. I'll likely clean that off. Other areas I should maintenance before replacing the switch?

Simply Red · 03-31-2014, 10:03 AM

PM Bob Dole, bud.

Garcia Bronco · 03-31-2014, 10:32 AM

Typically...and I am no expert....your furnace is overheating and it probably just needs ot be cleaned.

Jimmya · 03-31-2014, 10:45 AM

Does sound like over heating.

**Bugeater** · 03-31-2014, 11:24 AM

Make sure your cold air returns are clean and nothing is blocking them. If the system is really old it's possible that the evaporator coil is dirty as well. That's not something that I'd recommend the average person trying to do though.

plbrdude · 03-31-2014, 11:49 AM

most limits either automatically reset at around a 20-30 degree temp fall, or they are a manual reset. If yours is bad it could just be a bad switch. Or a thorough cleaning could help, air flow could very well be an issue. If it is gas and it's a flame roll out switch venting could be a problem. Make/fuel source/orientation (up flow or counter flow) would be good info to share.

Simply Red · 03-31-2014, 11:52 AM

Quote:

Originally Posted by Garcia Bronco

Typically...and I am no expert....your furnace is overheating and it probably just needs ot be cleaned.

gross New Chief.

Chief Roundup · 03-31-2014, 12:50 PM

Alright man lets get specific. Which limit switch is it? There should be 3 to 5 depending on age of the unit.
Determining which limit switch that has went bad will help to determine if there is anything else wrong. Parts do go bad and a limit switch/snap switch take a lot of temperature change but they do generally last a good amount of time.
Depending on which switch is what you should check to make sure there is no further issues. Check your filters and the cups in your squirrel cage of the blower assembly to insure you are moving the proper amount of air across the heat exchanger. Look for signs of the flame rolling out. Make sure your flew is not blocked or that the cap has not came off.
Of course there are many other things. But that is a start. Going to my late afternoon class. Will check back later this evening.

NewChief · 03-31-2014, 01:11 PM

Alright,

I crawled under the house and screwed with it a bit more, then I called in the HVAC guy. I don't have the time to mess with it right now, so I'll let a professional deal with it.

Thanks for all the suggestions!

Eureka · 03-31-2014, 02:58 PM

Majority of the time this is caused by a clogged filter. I see It all the time. Generally people won't notice there heater turning off and on until its to mate(part goes bad) If your heater is 10-15+ years old its prob one of those hi tech units that are no fun to work on and require an experienced tech.

Ad you called someone.

Chief Roundup · 03-31-2014, 05:37 PM

Quote:

Originally Posted by NewChief

Alright,

I crawled under the house and screwed with it a bit more, then I called in the HVAC guy. I don't have the time to mess with it right now, so I'll let a professional deal with it.

Thanks for all the suggestions!

When dealing with a gas furnace it is usually the best idea to let a licensed professional do the work that is necessary.

**srvy** · 03-31-2014, 06:34 PM

Quote:

Originally Posted by Chief Roundup

When dealing with a gas furnace it is usually the best idea to let a licensed professional do the work that is necessary.

Who want to do that when there is Youtube?

Chief Roundup · 03-31-2014, 08:21 PM

Quote:

Originally Posted by srvy

Who want to do that when there is Youtube?

Yeah that sure is nice in a crawl space or an attic full of insulation. Unless you want to make several trips in and out of one of those types of places.

NewChief · 03-31-2014, 08:25 PM

Quote:

Originally Posted by Chief Roundup

Yeah that sure is nice in a crawl space or an attic full of insulation. Unless you want to make several trips in and out of one of those types of places.

Hah. I was under the house with my phone watching youtube, calling parts stores, and finally calling the HVAC guy.

I probably would have barreled in and tried to do it myself, but I recently got burned trying to fix my dryer, going through two different parts orders, wait times on those, and then still eventually calling in a service tech to fix what I actually knew was the NEXT problem but was just too frustrated (okay, the wife was actually frustrated going to laundromat) to deal with myself.

**Bugeater** · 03-31-2014, 09:12 PM

Is it one of the sideways mounted to the floor joists sonsabitches? Gotta love laying on your side, usually in dirt while fighting them. I had to pull the burners from the last one I worked on, on a normal furnace that only takes a couple minutes, but it took me all of 20 minutes and cut up wrists and cuss words to get them out. And then repeat the process to get them back in.

03-31-2014, 09:53 AM
NewChief In Search of a Life Join Date: Aug 2001 Location: Fayetteville, AR Casino cash: $9690204	HVAC Limit Switch Trouble Shooting? Okay, I'm capable to buying and replacing the limit switch in my HVAC unit (I know that's what is wrong with it). My issue is that I don't want to just replace the thing and it get thrown again because whatever the original issue was hasn't been resolved. What should I be looking for that might have caused it to throw in the first place? I'd recently changed the filter, so I don't think that was it. It does look like there's a lot of built up dust around the fan unit, though. I'll likely clean that off. Other areas I should maintenance before replacing the switch?
Posts: 21,760

03-31-2014, 10:03 AM	#2
Simply Red You Sweetie! Join Date: Sep 2005 Casino cash: $2021206219 VARSITY	PM Bob Dole, bud.
Posts: 71,691

03-31-2014, 10:32 AM	#3
Garcia Bronco No Keys, No Problem Join Date: Sep 2000 Location: Denver Casino cash: $5213136	Typically...and I am no expert....your furnace is overheating and it probably just needs ot be cleaned.
Posts: 30,906

03-31-2014, 10:45 AM	#4
Jimmya Veteran Join Date: Dec 2012 Casino cash: $10024530	Does sound like over heating.
Posts: 2,743

03-31-2014, 11:24 AM	#5
Bugeater The Maintenance Guy Join Date: Sep 2005 Location: Renovated Bugeater Estate Casino cash: $6242680	Make sure your cold air returns are clean and nothing is blocking them. If the system is really old it's possible that the evaporator coil is dirty as well. That's not something that I'd recommend the average person trying to do though.
Posts: 70,443

03-31-2014, 11:49 AM	#6
plbrdude turd herder extraordiaire Join Date: Jan 2005 Location: hickville,mo Casino cash: $9997165	most limits either automatically reset at around a 20-30 degree temp fall, or they are a manual reset. If yours is bad it could just be a bad switch. Or a thorough cleaning could help, air flow could very well be an issue. If it is gas and it's a flame roll out switch venting could be a problem. Make/fuel source/orientation (up flow or counter flow) would be good info to share.
Posts: 2,249

03-31-2014, 12:50 PM	#8
Chief Roundup Admitted Planet Junky Join Date: Oct 2000 Casino cash: $1981627	Alright man lets get specific. Which limit switch is it? There should be 3 to 5 depending on age of the unit. Determining which limit switch that has went bad will help to determine if there is anything else wrong. Parts do go bad and a limit switch/snap switch take a lot of temperature change but they do generally last a good amount of time. Depending on which switch is what you should check to make sure there is no further issues. Check your filters and the cups in your squirrel cage of the blower assembly to insure you are moving the proper amount of air across the heat exchanger. Look for signs of the flame rolling out. Make sure your flew is not blocked or that the cap has not came off. Of course there are many other things. But that is a start. Going to my late afternoon class. Will check back later this evening. __________________ Fanaticism is nowhere. There is no tenderness or humanity in fanaticism.
Posts: 19,214

03-31-2014, 01:11 PM	#9
NewChief In Search of a Life Join Date: Aug 2001 Location: Fayetteville, AR Casino cash: $9690204	Alright, I crawled under the house and screwed with it a bit more, then I called in the HVAC guy. I don't have the time to mess with it right now, so I'll let a professional deal with it. Thanks for all the suggestions! __________________ In this world of sin and sorrow there is always something to be thankful for; as for me, I rejoice that I am not a Republican. - H. L. Mencken
Posts: 21,760

03-31-2014, 02:58 PM	#10
Eureka C Chiefs once a year! Join Date: Dec 2012 Location: Cali Casino cash: $2336097	Majority of the time this is caused by a clogged filter. I see It all the time. Generally people won't notice there heater turning off and on until its to mate(part goes bad) If your heater is 10-15+ years old its prob one of those hi tech units that are no fun to work on and require an experienced tech. Ad you called someone.
Posts: 7,507

03-31-2014, 09:12 PM	#15
Bugeater The Maintenance Guy Join Date: Sep 2005 Location: Renovated Bugeater Estate Casino cash: $6242680	Is it one of the sideways mounted to the floor joists sonsabitches? Gotta love laying on your side, usually in dirt while fighting them. I had to pull the burners from the last one I worked on, on a normal furnace that only takes a couple minutes, but it took me all of 20 minutes and cut up wrists and cuss words to get them out. And then repeat the process to get them back in.
Posts: 70,443