Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-24-2012, 12:56 PM   #16
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,489
Share |
Default

furnace cuts off, then on, then off...


You seem to be describing a main fan/limit control that is not limiting out. You could replace it but for the info you are giving, your furnace problems could also be from a number of other causes.
If you post actual photos of your furnace then the eagle eyes here might be able to direct you to other possible limiting switches. Have you bypassed your thermostat?
Do you have a meter?


Last edited by how; 09-24-2012 at 01:01 PM.
how is offline   Reply With Quote
Old 09-24-2012, 01:02 PM   #17
Member
 
Join Date: Jul 2012
Location: Toronto ON
Posts: 599
Default

furnace cuts off, then on, then off...


http://inspectapedia.com/heat/FanLimitSwitch.htm


the fan control has a hi temp limit function to cut off the burner if heat exchanger over heats..click on attached URL for details.. Read the symptoms/causes and make sure those are addressed first...However, from your description so far, I do think you need a new control.
techpappy is offline   Reply With Quote
Old 09-24-2012, 01:04 PM   #18
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,600
Default

furnace cuts off, then on, then off...


push the adjustment pins full CCW but hold that silver dial then reset the fan ON to say 100F and push the hi limit to the stop 200F-220F let the fan come ON see if the burner shuts off right after the fan comes on at 100FNOTE.... what temp the fan does come on off that dial and hovers at.if the burner shuts off right after the fan comes ON...change the control the contacts are aced or the bi-metal pig tail is wornout....measure the pig tail lenght before ordering it...your local Grainger has them
biggles is online now   Reply With Quote
Old 09-24-2012, 04:21 PM   #19
Newbie
 
Join Date: Sep 2012
Posts: 8
Default

furnace cuts off, then on, then off...


Quote:
Originally Posted by how View Post
You seem to be describing a main fan/limit control that is not limiting out.
Yes, that is consistent with my observations. I don't think it is the cause of the burner shutdown.

Quote:
Originally Posted by how View Post
You could replace it but for the info you are giving, your furnace problems could also be from a number of other causes.
Which brings me here to explore those possibilities.

Quote:
Originally Posted by how View Post
If you post actual photos of your furnace then the eagle eyes here might be able to direct you to other possible limiting switches.
I will try to post actual pictures. It might take me a few days, though.

Quote:
Originally Posted by how View Post
Have you bypassed your thermostat?
No - I have not. Do I do that at the thermostat?

Quote:
Originally Posted by how View Post
Do you have a meter?
I have a meter and I know how to use it.

Thank you - I hope to have additional information soon.
-dog
landog is offline   Reply With Quote
Old 09-24-2012, 04:57 PM   #20
Member
 
Join Date: Jul 2012
Location: Toronto ON
Posts: 599
Default

furnace cuts off, then on, then off...


starting from your original post all the information points to a defective fan control..IF..you have madse sure there are no air flow problems/blockages e.g., clogged filter, dirty fan, dirty A coil, blocked ductwork..which I presume you have verified as it has been mentioned.

It is not your stat because everything comes on in sequence as it should. It is only after the unit fires up that the burner "shuts off after 2 minutes" That means either there is lack of air flow causing the temperature in the heat exchanger to rise rapidly thereby cutting out the burner..as it is designed to do..then after it cools back down it repeats the cycle again..SO, it is either lack of air flow OR defective control ..nothing else

EXCEPT..maybe blocked venting or chimney? But, in that case there would likely be excess smoke or soot coming from burners and "roll out" of flame...
techpappy is offline   Reply With Quote
Old 09-24-2012, 05:00 PM   #21
Member
 
Join Date: Jul 2012
Location: Toronto ON
Posts: 599
Default

furnace cuts off, then on, then off...


you can check the power through the limit switch to see if the switch is opening the circuit it will only do so if temp is exceeded due to previously described possibilities OR if the switch is defective
techpappy is offline   Reply With Quote
Old 09-24-2012, 08:38 PM   #22
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,489
Default

furnace cuts off, then on, then off...


To eliminate the thermostat circuit as the potential problem...
Shut off power to furnace.
Follow thermostat wires where they enter the furnace. They should be connected to a wiring strip with the corresponding letters "R & W".
Disconnect one of those thermostat lines and move it where it can't ground on anything.
Now put a jumper, pigtail or tighten a piece of wire to connect the furnace "R & W" together.
Turn the furnace back on.

The furnace fire should run forever this way.

If it shuts off again like before, your thermostat circuit is not the cause.
Turn off the power and reverse it all the way you found it and its on to the next step.
how is offline   Reply With Quote
Old 09-29-2012, 10:10 AM   #23
Newbie
 
Join Date: Sep 2012
Posts: 8
Default

furnace cuts off, then on, then off...


There is an fan near the top of the furnace that connects to a small duct that leads to the chimney. There is a small tube from this fan that leads to a Tridelta pressure switch model FS 6017-26B. If I disconnect the pressure switch and jump the Normally Open output (after briefly jumping the Normally Closed output) the furnace runs normally.

If I connect a straw to the switch and suck with a meter connected to the switch - it seems to check out okay.

At this point how would I know if the switch should be replaced, or if I should look at whether the exhaust fan is not performing adequately?

I took the switch to my local parts store and they said they didn't have a replacement.

Any ideas?

Thanks,
-dog
landog is offline   Reply With Quote
Old 09-29-2012, 10:23 AM   #24
AKA HVACTECHFW
 
Join Date: Nov 2010
Location: NE Indiana
Posts: 2,317
Blog Entries: 1
Default

furnace cuts off, then on, then off...


call a pro!!!!!!!! In order to properly and safely diagnose your pressure switch problem the furnace needs to checked with a manometer.
__________________
IT IS WHAT IT IS
hvactech126 is offline   Reply With Quote
Old 09-29-2012, 01:18 PM   #25
Newbie
 
Join Date: Sep 2012
Posts: 8
Default

furnace cuts off, then on, then off...


Quote:
Originally Posted by hvactech126 View Post
call a pro!!!!!!!! In order to properly and safely diagnose your pressure switch problem the furnace needs to checked with a manometer.
The "pro" that looked at my furnance last year checked it out for about an hour, then told me its operation was normal and charged me for "cleaning."

While I understand your viewpoint, I think I'm much further along toward a solution than the pro.

Thanks,
-dog

Last edited by landog; 09-29-2012 at 07:05 PM.
landog is offline   Reply With Quote
Old 09-29-2012, 03:32 PM   #26
AKA HVACTECHFW
 
Join Date: Nov 2010
Location: NE Indiana
Posts: 2,317
Blog Entries: 1
Default

furnace cuts off, then on, then off...


Then you obviously didn't hire a "PRO". If you were having this problem while he was in the home checking the unit and he called it normal operation then he was obviously not a pro. You need a manometer and to know how to use it in order to properly check the operation of the pressure switch and then from there determine the correct diagnostic path to follow. A number of things could cause your pressure switch to not operate properly or it may be the pressure switch itself that is bad. You CAN damage a pressure switch diaphragm by blowing or sucking on the tube.

__________________
IT IS WHAT IT IS
hvactech126 is offline   Reply With Quote
The Following User Says Thank You to hvactech126 For This Useful Post:
ben's plumbing (09-29-2012)
Reply

Tags
amana, ghi90a30, s8910u


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quote for new furnace. Reasonable? dengle HVAC 16 03-04-2012 07:01 AM
Carrier Infinity 69 Trouble Code 42 bodya1 HVAC 4 12-05-2010 06:43 PM
Problem with Trane gas furnace quovadis HVAC 17 12-22-2008 01:12 PM
Olsen BFL 120 Furnace DaleB HVAC 12 12-19-2008 10:42 PM
Furnace question cuts off until I hit the reset switch bmvrdv HVAC 7 12-09-2008 09:54 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.