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-   -   Heat comes on but blower never does (http://www.diychatroom.com/f17/heat-comes-but-blower-never-does-4877/)

aczer 11-18-2006 02:37 PM

Heat comes on but blower never does
 
I am new here, so I hope I am posting in the right place. My Snyder General gas-fired furnace (model GUD 060A014AIM, mfg date 6/91) stopped working a few days ago. I went online and started to learn about home heating. I determined that the igniter was defective and replaced it. So I am proud to report now that when I switch the thermostat to Heat, the gas flows, the igniter glows, and there is hot air.

However, the blower never comes on, and so the hot air only comes out of the register in the room which is located directly above the furnace. There is almost nothing emerging from the other registers.

The blower does operate if I move the fan switch on the thermostat from Auto to Manual. Of course when I do that the blower keeps going even after the heat turns itself off (when the set termperature is reached). The blower turns off as soon as I move its switch to Auto.

I just tested what happens if I switch the thermostat from Heat to Cool and set the temperature lower. In that case the blower and the compressor outside both come on immediately.

I thought I might have accidentally pulled off some wire down there on the side of the blower while I was working on the igniter, but I cannot see anything that seems loose.

What should be my next step to solve this heating problem?
Could this be a thermostat malfunction or is it something down there on the blower unit?

I would guess there might be some danger in letting the furnace operate without the blower - is that right?:eek:

While trying to figure things out, I took the thermostat off the wall and noticed that there is melted plastic on a back corner of the thermostat. Is that a clue?

Any guidance will be very much appreciated!

Justin1635 11-18-2006 08:58 PM

your furnace should shut off after a certain amount of time if the blower doesnt work. this is usually dont by a heat limiting switch, after this problem is fixed, i suggest you also have that checked out.

anyway for the blower, it doesnt sound like the actual unit is having a problem if you can force it on with the tstat. it sounds like your anticipator is shot?

what model thermostat is it

aczer 11-18-2006 09:39 PM

The thermostat is a 10 year old Maple/Chase which looks very much like my 3 year old Robertshaw thermostat upstairs. The only difference I can see is that the newer thermostat has a fuse inside, whereas the older one has no fuse that I can find..

I am assuming that I should expect the following behavior to be "normal" for the heater cycle:
  1. thermostat sees that current temp is below desired temp, so it "calls for" heat
  2. the control box sends current to warm the ignitor,
  3. the control box allows gas flow, and then the main burners light
  4. the control box must detect main burner flame pretty soon or else it shuts off both the gas and ignitor
  5. if it detects the main burner flame, it leaves the gas flowing and the burners burning until the thermostat stops calling for heat
  6. the blower does not come on immediately but should start up sometime after it detects heat being produced
  7. the blower should continue to run for a short time after the heat shuts down, to purge the system of gas
Is that correct?

Where can I find the heat limiting switch?

What is an anticipator, and where do I find it?
Thanks.

#CARRIERMAN 11-19-2006 01:55 PM

Hi aczer

Stop what you are doing! If the anticipator is out of a thermostat you will not fire up the heater at all. I am not sure where justin is getting his schooling from but a digital stat does not have a mechanical aticipator, it has a software anticipator. Even though the Maple Chase is a cheap thermostat in your case it is not bad. You are bringing the gas part of the furnace on. What is wrong with your furnace is it either has a bymetal fan switch that is sticking or is has a blower board that is not working properly. The bymetal switch I am talking about is a piece that will be setting towards the middle of the furnace and is about 3" wide by 6" long and has Honeywell on the cover, if you have the bymetal it will have a round dial, if you carefully turn this dial and return it back it should make a clicking sound, do not move the little pins sticking through the dial. If it has the blower board leave the blower on until you can get a new one. Either way you will need to replace the defective component.

Good luck
Rusty

aczer 11-19-2006 03:53 PM

Thanks for pointing me in a new direction. I found the "fan and limit control" about half-way up the furnace. It is hard to see and reach, but it has a round dial and I think some pins. After unplugging the power, I can reach up and turn the dial in both directions. It is spring loaded, and returns to its original position, so I only turned it very gently, did not hear any clicking. Anyway, I made sure that it does turn a little bit in each direction, but perhaps I did not turn it enough. Should I go back and turn until there is a definite click?
According to my Snyder General parts list, this thing is called Fan & Limit Control L4064E-2403 190 and has a part number 130061.

The control has four wires: red, black, yellow, and pink. The red wire goes to two little chips, one above this and one below. I think these are called a Flame Roll-out switch and look as if they each have a reset button.

Anyway, all four of those wires are harnessed together and run through a grommet into the bottom of a metal box on the side of the blower.
Inside the box I would expect to find the Blower Relay and the 120 to 24 VAC Transformer.

Is that box where the "blower board" would be?

I did not remove that box in my earlier fix of the igniter, so I doubt that I pulled any wires inside; but I could pull the box off and look inside. The metal box has connectors on the outside of it, and all those connections seem tight.

Thanks for any clarification.

#CARRIERMAN 11-19-2006 04:02 PM

Hi aczer

You found the right part. In your case you don't have to worry about the blower board. If you turned the switch as far as it would go without damaging it and you did not hear a click. There is no doubt it is bad, when you go to replace it if you use the Honeywell number, that is the L4604 part #. They will be able to get you a replacement. The aftermarket ones are generally cheaper. If you have a Johnstone supply in your area or something of that equivalence, you should have no problem getting one. Good job on diagnosing.


Good luck
Rusty

aczer 11-19-2006 04:15 PM

1 Attachment(s)
I looked around on-line to try to find a picture of my fan limit control. I found one picture on the web (attached). Here is the URL where I found it.
http://toad.net/~jsmeenen/blower.html#camstat
It seems to have the same dial as my control, but I have not taken my control out of the furnace yet, so I don't know what type it is inside. I have learned that there is a temperature probe on the inside of the furnace which provides the input to this unit, the probes come in different lengths. But I am having difficulty finding my exact model number on the internet, perhaps it has been replaced by newer model numbers.

I am wondering if my replacement of the ignitor could have caused a problem with the fan limit control. What are the odds that both components would fail at the same time?

#CARRIERMAN 11-19-2006 04:38 PM

Hi aczer

Replacing the ignitor did not cause the problem, actually nothing you have done to this point caused a problem. The bymetal coil that sticks into the furnace actually get the crap kicked out of it every time the furnace is on. The probe that is on the back of it is in the air stream so it not only has air running across it in the winter but also in the summer. It also is a mechanical device, it has been working I am assuming for 15 years now. Heck I myself in the last 15 years went from a vibrant young man to a grouchy old fart. When you go to get a new one take the old one with you, note the red and yellow wires in the center. This fan/limit has a heater built into it, you will need to make sure they give you one exactly like this. This part is not hard to get out of the furnace, all you will need is a 1/4" nut driver and a small tipped flat screwdriver. Please make sure you have power off to furnace while working on this part. If you look you will see one side marked fan and the other marked limit. The fan side has 120 volts on it and the limit side has 24 volts on it. I would not be happy if I allowed you to hurt yourself because I forgot to warn you of something. When you get the new switch there will be a brass tab in the middle of the switch just below where the red and yellow wires hook up. You will need to use a pair of needle nose plyers and break this tab out, If you forget to it will destroy your transformer and probalbly your thermostat! You can also get this one from a Lennox dealer, they used this exact switch on their units also. I am not sure about your area but going to a parts house is going to be a better choice simply because they have to deal directly with you. Less likley for you to get the wrong part. Let me know if I can help any further.

Good luck
Rusty

Justin1635 11-20-2006 12:11 AM

Quote:

Originally Posted by #CARRIERMAN (Post 24142)
Hi aczer

Stop what you are doing! If the anticipator is out of a thermostat you will not fire up the heater at all. I am not sure where justin is getting his schooling from but a digital stat does not have a mechanical aticipator, it has a software anticipator.

if you read my post, you woulda seen that i asked him what type of thermostat he had, i didnt say that it was his problem. i simply thought if he had an older stat, it might be causing some problems.

aczer 11-21-2006 03:10 AM

My thanks to both Justin and Rusty. Here is my update: I removed the fan limit control, and went to Johnstone Supply out on the edge of town. They sent me away, saying they would not sell anything to anyone who is not a licensed contractor. But I was able to get a new fan limit control at a different appliance parts store. The two people at the counter there looked at my old part, and went right for what they said was the only L-shaped cardboard box on the shelf. They only had one in stock, and both of them said that this was the first time they have sold one -- for $108 including tax.

Installation was straightforward, and now... the furnace seems to be working OK! Hooray and many thanks.

I believe that the thermostat is OK since it seems to turn the furnace off and on for heating and for cooling.

By the way, I learned another thing from this project. It seems that the blower has at least two speeds. The lower speed is what comes on when the fan limit control detects hot air. The higher speed comes on when the AC is pushing cool air, and the higher speed also comes on when I push the fan switch from Auto to ON at the thermostat. Is that normal?

I really appreciate all the advice. I spent $166 for parts, avoided buying a new furnace (for now). I assume that a service call to a local HVAC company might have cost much more, and possibly talked me into an entirely new furnace (would that be in the ballpark of more than $2,000 ??)

I have already told my friends and family about this helpful website. Thanks again.

#CARRIERMAN 11-21-2006 10:43 AM

Hi aczer

First I would like to thank you for writing back and letting everyone know how you were able to repair your furnace. And second I am glad we were able to help you. As far as the fan speeds, most blower motors have either 3 or 4 speeds you can choose from to give you proper air velocity. I could give you hours of lecture on enthalpy, but once again not sure if the server is big enough. Just wanted to say have a safe and happy winter.

Good luck
Rusty

aczer 11-21-2006 03:37 PM

I feel it is important to share all of the learning, one never knows if the next guy who comes along will have the same problem and will find the solution here.

Thank YOU, and Happy Thanksgiving.

jer_maynard 02-13-2011 07:57 AM

check the start capacitor for the blower motor
 
i recently saved alot of money on a service call. the heating element would get hot and stink up the place because the blower wouldnt come on at all. the blower start capacitor is a little silver block wired from the blower motor itself, mine looks like a 9vlt battery in shape .I used an ohm meter and verified loss of continuityand replaced it. the part cost me 9 dollars at the part store. the service estimate was $70 , diagnostics $50 , part and replacement $50 and i was broke till friday. my wife bragged on me like i was a hero
I hope this helps .
god bless


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