I’ve been having the following problem with my fan/limit switch: the blower doesn’t turn off when the “fan off indicator†goes past the “temperature mark†on the body of the unit. I’ve watched the “scale plate†when I’ve turned off the heat and when the “fan off indicator†hits the “temperature mark†I see it “jump†as though its “triggeredâ€. Also, I can get the fan to turn off by manually rotating the “scale plate†or the moving the “fan off indicator†back and forth past the “temperature mark†(I feel it “trigger†when it turns it off), so I know its not an electrical problem.
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I called the manufacturer and he told me to contact a pro but I think this is a simple issue that I can solve with your help!
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The unit is a Honeywell L4064A and the manual can be found at: http://www.honeywell.com/ <!—->sites/servlet/com.merx.npoint. <!—->servlets.DocumentServlet? <!—->docid=DB6EDE2B5-389C-8487- <!—->0644-73BD77880C46
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Thanks for any advice you may have, Mischa
Replies
The low temp limit switch is bad. Replace it and the check the fan run/off switch.
The fan comes on at the run temp and should run for a few minutes after the t-stat says it is satisfied. That is to get more heat out of the heat exchanger and cool it down to the off temp on the limit switch.
Your unit could have both a fan on and a fan off switch. The on one will rated at the higher temp and the off one at around 120-130 degrees F.
Edited 10/29/2008 12:52 pm ET by DaveRicheson
Can one replace the "low temp limit switch" without replacing the whole fan limit unit? If so, do you know where I might go to get directions on this? Or, are you saying I should replace the whole unit?<!----><!----><!---->
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Thanks, M
All i got on your link was the Honeywell home page, so didn't get a look at your specific fan limit switch. It could be that yours is a single unit with both upper and lower switches built into it. Without a schematic of the switch or the even the furnace it would just be wag to say replace it.
If you can give a link to the specific switch or the schematic for the furnace it would help.
Maybe Bill Hartman or Dan H will come long and help us out.
Assuming this is the classical Honeywell unit with a rotating disk inside with fan off, fan on, and high limit adjustment levers around the perimeter:
First I'd try nudging the fan off (low temp) setting up a little (5-10 degrees). (Don't forget to hold the temp disk when adjusting!!) If that doesn't fix it I'd just replace the entire control, rather than worry about it.
It is a classic with the disk inside.I've tried that so it sounds like I need to replace the unit. Any recommendations on a book or website that addresses how to remove and install a fan limit unit?
If it's the unit I'm thinking of you just take out a couple of screws (through the back of the case). Disconnect and reconnect the wires in the same order they were in. (Don't forget to shut off the power first.)But before you do this, does this unit have AC? If so there's generally a fan relay that could be sticking and causing the fan to stay on. It's probably a plug-in relay attached to the side of the case, just above the fan chamber. Simply pulling out the relay (with the power disconnected) and then trying the furnace will confirm whether or not the relay is at fault. (You only need the relay for AC, not heat.)
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
No A/C (we are in upstate NY; no need :)<!----><!----><!---->
Regarding purchasing the new unit:<!----><!---->
· Are there any compatibility issues I should be aware of when I purchase a new unit?<!----><!---->
· Any recommendations for a good unit/seller?<!----><!---->
It's a pretty standard unit. Just try to get the model number off of it, and the basic dimensions. Or take it with you when you shop.Anyone who carries HVAC parts should carry it.
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
Right on. Thanks again!
So this is the unit I'm planning to buy, seems straight forward but I don't want to end up with the wrong thing: http://www.simplyplumbing.com/honeywell-l4064b2210.html
The various units differ by how long the temperature probe is on the back. That's probably the one thing you have to get right. That's where a model number is handy.
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
And a big thanks for you help!