Sometime last winter, we had the HVAC guy come in to clean our furnace (we try to do it once a year). At the time, the fan limit switch wasn’t turning the fan off. The guy convinced me that I could do it myself. Well a year later, I still haven’t fixed it. We just keep the fan on all the time. We kind’a like it. Helps keep all the rooms the same temp – no hot or cool spots.
Well, another guy came in the other day. He started to try to convince me to replace the switch myself just like the other guy. I’m sure I can do it, but why are these guys trying to get out of the work? Any insight would quench my curiosity.
That being said, I also need some help picking out the right switch. I can buy from Grainger and they have a location nearby. I don’t mind paying a little extra for the convenience.
thanks
Joe
Replies
Well, if your a cynic, you might think they want you to change it yourself so that you can break the furnace even more and then hire them for changing the whole thing and not just a switch.
Or it could be that they want your business in the future so saving you a few bucks now might convince you to use them later.
Also, HVAC guys are really busy at this time of the year (in the north anyways) so I figure turning down small jobs is not hurting too much.
Is your furnace still under warranty, by the way ?
No, not under warranty. I think it's orginal to the house, built in '74. We are planning a new one sometime next year.
It was strange how they both wormed out of doing the work in the same way.
Wow, a 34 year old furnace. That's pretty good.
The guy couldn't find the year in the serial/part number. None of the duct work looks like it's been changed. Between the he and I, this was our guess that it was original.
(I didn't get a warm fuzzy feeling from him when he couldn't pinpoint the year a little better)
The limit switch should have a mfg. and part no. on it. Pull it out and take it to a supply house to match it up with a replacement.
My take is both were saving you some $$ and themself a ton of time. They would have both had to charge for the run and pickup time. Parts for old units aren't always in stock, so they have to wait while the counter guy searches, either on line or manufactures books, for the correct repalcement. Then if it has to be ordered you getanother charge and another service run charge.
Not being able to find the mfg. date in the serial number is no big deal. some use actual numbers, others letters, and still others a combination as a code. If they don't service that particular brand frequently, it is easy to forget who does what.
It is a Honeywell, should be easy to find. (famous last words)
Betcha ya kind find it on their web site and then cll arounf. Those old war horses are still used alot.
thats when furnaces had about 6 parts and thats all that could go wrong. i have probably a 1/2 dozen that were put in in the mid 50's.just put a thermocouple in one this am. 4.00 and it's fixed.
yea i know i could buy new and save energy, well by the time i buy anew one,buy a computer baord evry 5 years, a ignitor every 3-4. it will take a long time to even out,and i'm working on a 20 year plan right now. in 20 years i'll be drulling all over my self and could care less.if a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
Wow, a 34 year old furnace.
My 52 y/o FAG furnace was still working fine when I replaced it last summer. My 20 y/o A/C died and I decided to put in a heat pump w/ 93% eff. gas back up. I think I wasted my furnace money. The heat pumps works fine down to about 18F. The gas has only been on once this year.http://www.quittintime.com/ View Image
It might be that they don't have the switch on their truck, so they know they would have to go get one and come back, and they probably don't get to charge for the extra work.
Or occasionally, they know that the price they charge for the switch is outrageously high, and they know that if you find this out, you will get mad at them. I had that regarding an ice-maker.
Some of those have a little white button on them... and it will say something like "push manual, pull auto".
If the little button is pushed in, the fan will stay on all the time.
Two guys have told me the coil inside is shot. It won't turn off without a wack on the side of the furnace - not a practice I would like to continued basis.
The switch is pretty standard, the main difference being the length of the probe that comes out of the back to sense temperature. Simplest thing to do is to remove the unit and take it with you to match up. Just be sure to label the wires, or somehow keep track of how they were arranged.
When setting up the new unit, be sure to hold the round dial steady with one hand while moving the indicator levers with the other -- if you don't do this you bend the thermostat element and wreck the switch.
Edited 11/14/2008 6:09 pm by DanH
Finally got my limit/fan switch swapped out today. Piece of cake. The weather was warm enough that I could have the furnace off for a while (couple of hours if needed). So I was confident I had time to get it done. Even though the furnace is ancient, the switch was identical.
That being said, now I want to get my humidifier working. In a nutshell it doesn't turn off. It's an Aprilaire connected to the hot end of the furnace, pretty standard I think. The control is connected to the return air duct.
Two questions...
One, what would stop the humidifier from turning off?
Second, shouldn't the humidifier stop when the furnace fan stops?
The humidifier is controlled by the humidistat. If the humidifier doesn't shut off as you turn down the humidistat, either the humidistat is defective or it's miswired.The humidifier should not run when the fan is not running. Either the humidifier should be rigged with a current transformer (in series with the humidistat) to keep it from running when the fan isn't running, or the humidifier should be wired to turn on the furnace fan when the humidifier runs.If the humidifier is rigged to run when just the furnace fan is running (no heat), it should be piped with hot water. But only if it's a brand (eg, most AprilAire models) that's rated for hot water.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Thanks for the response.
I think the humidistat is not working. It never shuts off or turns on automatically. That being said, it still shouldn't run when the fan's off.
I checked it out and the humidistat is connected directly to the humidifier but nothing else. The humidfier has no other connections - nothing to turn on/off the fan or to detect if the fan is running.
Anything else I should be looking for?
Joe
Turn the adjustment knob on the humidistat all the way down to "Off" and see if that turns off the humidifier. If not then probably the unit is miswired. If you can turn it off (suggesting that the wiring is essentially correct), then turning the knob slowly higher should cause the unit to come on when the knob reaches the ambient humidity. Failure to do that would suggest that the humidistat is defective.To bring the unit on with the furnace fan, you need a Model 50 24V current relay from Research Products Corp.What model of humidifier do you have, is it the bypass type, with a tube that runs between the supply and return plenums, or the stand-alone type with a built-in fan? Is there a 120V power cord coming out of the unit, or does it use the furnace transformer's power?
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
The humidifier turns on and off when I turn the knob. It just never does it by itself.
It's a stand alone with a 120v plug. Aprilaire model 760.
The humidifier isn't going to work right if the fan isn't running. You probably need to get the Model 50 current relay to turn the unit on with the fan. Then the humidistat will have a chance to work right. (The wiring diagram is on the Aprilaire web site, IIRC.)The only problem is that the lashup will then not effectively humidify in the "shoulder" periods of spring and fall. To fix that you can add a relay to the furnace to bring the furnace fan on when the humidistat calls for moisture, but that's a bit involved.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
I would actually want it to run less than more. So having it run just in the really dry months of dead winter would be fine. I'm not really picky about humidity (dw is though), so if I could just control the worst case scenario, I would be happy.
I went to the Aprilaire site (which s&*%s) and couldn't find the relay you mention. Do you have a link?
Thanks for all the help!!
Why the heck the Aprilaire folks don't sell the relay (or vane switch, which accomplishes the same thing differently) with the unit, I don't know. And you can't find them at any big box, you have to go with an internet order. Here's a source that I got with Google:http://www.amazon.com/Generalaire-Aprilaire-50-Current-Sensing/dp/B000XM4BB4Here's another source that I've used before:http://www.arnoldservice.com/humidifier_parts.htm(Aprilaire relabels the box, but it's a Research Products unit when you open it up)It's a little tricky to wire up, because you need to dig into the motor wiring on the furnace. If you're not comfortable with that you might want to call a pro (or a semi-pro buddy) or use a vane switch. (Unfortunately, I can't find a link to a vane switch.)Here are the relay install instructions (though my old Acrobat couldn't open the reference):http://www.alpinehomeair.com/_viewresource.cfm/ID/81/p/Aprilaire%2050%20Relay%20Installation%20InstructionsHere's another, though fuzzy:http://www.gogeisel.com/geiselonline/support/Aprilaire_Humidifier_Information.htmlHere's clear instructions for the 120V model 51:http://docs.electronicaircleaners.com/aprilaire_51_installation.pdf
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Ok Dan, one more question.
This might be a dumb question (or scary from an electricians point of view), but how do I know if I need a 24 volt or a 120 volt relay? I'm assuming since the humidifier is plugged straight into the wall that I would need a 120, but I don't know if the voltage is changed inside the unit.
thanks
You put the relay in series with the humidistat. The humidistat is powered from a 24V transformer in the humidifier. The relay should be 24V.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Makes sense, thanks for all the help.
I got my model 50 in the mail.
I found my common wire on my blower, easy enough to put the relay around the wire.
When I put the relay in series with the humidistat, does it matter which wire I connect to? (I think I just heard the collective cringe from the electricians in the forum)
No, doesn't matter. The low-voltage cable between the humidifier and the humidistat isn't "polarized" in any meaningful way, so either wire can be switched by the current relay.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
That's what I thought, so I fixed it this morning.
I should have done this years ago. It was way too easy.
I am so tired of refilling our little humidifier that sits in the hallway. Now I just have to convince the DW that it's not needed anymore.
Thanks for the help,
Joe
Glad to help.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel