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 10-13-2012, 01:00 AM   #1
Newbie
 
Join Date: Oct 2012
Posts: 9
Rewards Points: 10
Default

fan limit switch?


I have a older early 80's carrier furnace model number 349FAD036075 if that helps. I turned the heat on for the first time this year a couple of days ago lit the pilot and turned the heat up. when I did everything started fine. Burners lit good and after about 30 sec the fan kicks on. After 20sec the fan cycles off but the burners stay lit. The fan continues to cycle on and off at different intervals of time while the burners continue to stay lit? Had a local hvac guy come by today. Looks at it and says he seems to think its the fan limit switch. He called me back later today and said that he can't locate a fan limit switch for the furnace that it must be discontinued?? So I'm stuck wondering is there a aftermarket fan limit switch to work with this furnace or is it even the fan limit switch that's malfunctioning? Or im looking at replacing the furnace which i dont want to do. Thanks for any help

jbrown0902 is offline   Reply With Quote
Old 10-13-2012, 01:05 AM   #2
Newbie
 
Join Date: Oct 2012
Posts: 9
Rewards Points: 10
Default

fan limit switch?


Also...blower works fine when cut on manually from thermostat and had no problems with the AC working this summer.

jbrown0902 is offline   Reply With Quote
Old 10-13-2012, 03:43 AM   #3
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,498
Rewards Points: 512
Default

fan limit switch?


A picture of the furnace with the doors off would tell me if your fan/limit control was bimetal or a board. Did your tech give you the number of the fan/limit control he was looking for?
If it's a bimetal fan/limit control, some possibilities are
*your heating fan speed is too fast and is shutting off the temp fan control
*The temp nibs on the fan/limit control are out of adjustment
*the fan/limit control is faulty
or
*the gas pressure is too low.
how is offline   Reply With Quote
Old 10-13-2012, 06:58 AM   #4
Member
 
Join Date: Sep 2010
Posts: 453
Rewards Points: 252
Default

fan limit switch?


My furnace acts similarly after being off for warm season. After a few cycles, returns to normal with no fan cutouts.

I would wait before ordering a switch and see if it improves.
diyorpay is offline   Reply With Quote
Old 10-13-2012, 07:20 AM   #5
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000
Default

fan limit switch?


might be either one of these...the first one check the pin setting for fan ON might of moved during the season http://bestbuyheatingandaircondition...ry_Code=fl-5fl local Grainger has fan controls should be open today worth the trip...check out where they are around you... or this style non-adjustable http://bestbuyheatingandaircondition...ry_Code=fl-tdf ... both work on metal reacting to heat and closing/opening NOTE heating fan isn't thru stat but these 2 controls if jammed use FAN/ON with heating mode but will end up drafting when stat satisfies..control hasn't moved since last winter heat cycle..lets hear back what you might have...you have 2 limits there.... FAN and HI-LIMIT burner

Last edited by biggles; 10-13-2012 at 07:25 AM.
biggles is offline   Reply With Quote
Old 10-13-2012, 10:44 PM   #6
Newbie
 
Join Date: Oct 2012
Posts: 9
Rewards Points: 10
Default

fan limit switch?


This is what I have
Attached Thumbnails
fan limit switch?-2012-10-13_23-33-55_187.jpg   fan limit switch?-2012-10-13_23-34-27_713.jpg   fan limit switch?-2012-10-13_23-34-46_996.jpg  
jbrown0902 is offline   Reply With Quote
Old 10-14-2012, 12:10 AM   #7
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000
Default

fan limit switch?


that control behing the terminal strip is the fan limit control and senses the burner section behind the panel where it is mounted.... it is is old as dirt and the range is low on the setting and temp range making me think you have a disc type someplace else....this control runs the fan on/off from the heat build up and cool off during a cycle....can you give us that number off that limit control...looks like FAL??? something.it definitly can be replaced with another we'll get you there... searched it...here http://www.comfortgurus.com/product_...oducts_id/1509 with pix at the bottom of the info page to view.if you can't get this one just google "fan limit switch" then view images to see all the types that will link you to the suppliers

Last edited by biggles; 10-14-2012 at 12:28 AM.
biggles is offline   Reply With Quote
Old 10-14-2012, 02:39 AM   #8
Newbie
 
Join Date: Oct 2012
Posts: 9
Rewards Points: 10
Default

fan limit switch?


OK I just went and got the number off of the fan limit control its FAL3C-05TD-120-A and it was set between 85 and 100 degrees the hvac guy was messing around with the fan tempt cut off on the limit switch dont know of he put it back where it should have been. Also noticed tonight when trying the heat again that the small black box with a small clear red dot on it furthest top right in the picture makes a rattling noise when the blower does kick on? Thanks for all the help!
jbrown0902 is offline   Reply With Quote
Old 10-14-2012, 03:39 AM   #9
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,498
Rewards Points: 512
Default

fan limit switch?


Try turning that fan control clockwise to a lower temp. to see if that changes your fan's short cycling. They often do weaken with age and require adjustments.

I think the other control with the red dot might be an isolation relay which is an electromagnet switch that allows a 24 V current to control a 120 V circuit.

Last edited by how; 10-14-2012 at 03:52 AM.
how is offline   Reply With Quote
Old 10-14-2012, 03:45 AM   #10
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,541
Rewards Points: 2,762
Default

fan limit switch?


Need a new Cam Stat. There still made.
beenthere is offline   Reply With Quote
Old 10-14-2012, 07:01 AM   #11
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000
Default

fan limit switch?


is the schematic still living on the back of that cover ID that relay and get back on here...100F is low compard to other furnaces with a fan limiting switch...must be the design of that furnace.the higher you set it (which isn't much more) the discharge air into the space will be hotter,and the stat will satisfy.tweek it up to 120F check how the fan acts then...if you can read the discharge air above the furnace in the supply duct as close to the heat exchanger to get an idea at 100F then change the controller to 120F+ full CW..that red dot relay only has 4 wires to it COIL and pair of contacts isolating something...the other relay with the colored wires to the terminal point out is the fan relay in cooling for Hi fan...NOTE heating is always either LO or MED fan speed.if you have a volt meter might read that black or brown wire to ground when the fan is running to see what drops off or go across those 2 when the control opens the fan will shut off or the meter will read something...

Last edited by biggles; 10-14-2012 at 07:14 AM.
biggles is offline   Reply With Quote
Old 10-15-2012, 12:28 AM   #12
Newbie
 
Join Date: Oct 2012
Posts: 9
Rewards Points: 10
Default

fan limit switch?


This is the best shot of the schematics I could get. Will be ordering the new fan limit switch shortly...still don't know if the relay with red dot on it is going up also....seems to be making more of a weird rattling noise when the blower kicks on then yesterday when trying it. Don't know if that's normal or not. Tried lowering the fan temperature cut off to see if it would do anything different...no change
Attached Thumbnails
fan limit switch?-img_20121015_013510.jpg  

Last edited by jbrown0902; 10-15-2012 at 12:36 AM.
jbrown0902 is offline   Reply With Quote
Old 10-15-2012, 01:35 AM   #13
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,498
Rewards Points: 512
Default

fan limit switch?


Normally turning the temp control of a fan control low enough should make the fan run forever. I'm assuming that either something is faulty with the fan control which is making it non adjustable or another cause is cutting power to the fan motor. I have seen fan controls set up with 24V which then ran through an isolation relay. Just because you've mentioned several times how noicy that relay is, does a wire from the fan control go to that relay?
how is offline   Reply With Quote
Old 10-15-2012, 06:44 PM   #14
Member
 
Join Date: Oct 2011
Location: pa
Posts: 4,436
Rewards Points: 2,186
Default

fan limit switch?


you can use this as a guide.....johnstone supply...4-5 different one still made to fit your furnace..ben sr
Attached Thumbnails
fan limit switch?-002.jpg  
ben's plumbing is offline   Reply With Quote
Old 10-15-2012, 08:16 PM   #15
Member
 
Missouri Bound's Avatar
 
Join Date: Apr 2011
Location: Almost Arkansas
Posts: 2,764
Rewards Points: 2,000
Default

fan limit switch?


Quote:
Originally Posted by jbrown0902 View Post
Also...blower works fine when cut on manually from thermostat and had no problems with the AC working this summer.
Sure sounds like a limit switch. I"m surprised a furnace 20+ years old only has that issue.

__________________
Do you want it your way or the right way?
Missouri Bound is offline   Reply With Quote
Reply


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
Bryant 311AAZ036070 Limit Switch Problem coleary61385 HVAC 5 02-24-2012 05:01 PM
furnace limit switch question diyheat HVAC 29 02-18-2012 07:18 PM
Furnace limit switch jk55 HVAC 5 03-03-2011 04:23 PM
heil 9000 limit switch problem? barryatnewton HVAC 1 01-02-2010 05:44 PM
Replacing a bathroom fan switch cmacjr22 Electrical 4 11-04-2008 06:14 PM




Top of Page | View New Posts

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