Gas Furnace Problem

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Old 02-02-13, 08:28 AM
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Gas Furnace Problem

Hi,

Our gas furnace at home seems to be having issues- the flames come on okay, but the blower does not.

From the thermostat, I can turn on the fan independently, and that seems to work just fine- so my guess is that whatever timer tells the blower to turn on after the flames have been on for 30s or so is kaput.

The heater is a Rheem- I'm attaching a photo.

Is this something I could maybe fix myself? What do I need to do?

Thanks
 
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Old 02-02-13, 09:03 AM
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A model number could be helpful.

I can't see from your pic if your unit uses a conventional fan/limit switch like the picture below. This switch would have a silver cover over it.
 
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Old 02-02-13, 11:05 AM
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I didn't see anything that looked like that... I took some more shots of everything I saw inside... hope it helps.
 
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Old 02-02-13, 11:47 AM
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Remove the top furnace panel to look for a fan limit (as shown by PJmax) or cam stat.
Should be there or under the angled panel the is partially covering the flex gas line in your pic.
 
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Old 02-02-13, 07:36 PM
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Found it! Okay, so it looks like the red wire (the curved one) is fried where it inserts into the black thingie. At least it was very crumbly and then when I gave it a gentle tug it popped out.

I dont see any way to re-attach it. Does that mean I need a new fan/limit switch?

What next?

Thanks!!
 
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Old 02-02-13, 07:45 PM
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Yes....it looks like it's seen better days. Looks like heat marks on the switch.

What you can do is leave it in for now because it's still protecting the furnace from over heat (black wiring) and leave your fan switch on FAN ON.

Order and replace the control.

Is there a part number on it. Online stores don't seem to list it by furnace model.
 
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Old 02-02-13, 08:33 PM
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Great!

So I found the part (I think) here

The actual number is in the photo..

Im a bit concerned however- it looks like the red wires are permanently attached to the switch- and then the go directly in to the box on the left (in the picture). Is this a problem to replace?

I currently have the furnace completely unplugged from the wall and gas off. The thermostat is also off. Lucky I live in San Diego where nights arent too cold.

Any words of warning or advice? I'm pretty handy, and have soldering stuff but I was a bit surprised the wired weren't connected with screws or some other easy-to-remove connector.

Thanks!
 
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Old 02-02-13, 08:44 PM
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Looks like you have located the correct part.

The wires just "push in" to the terminals.
You would cut them off at the old switch.......strip them maybe a half inch......if you have a soldering iron you could lightly tin the wires so that they don't unravel as you push them in to the new switch.
 
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Old 02-02-13, 09:38 PM
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Excellent!

A HUGE thanks to PJmax and Houston204. I shudder to think how much this would have cost had I called someone out to fix it.

It's not done yet of course, but I'm 99% sure this will take care of it.

Cheers!
 
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Old 02-02-13, 10:05 PM
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Some limit switches come with a jumper between the fan side and the limit side of the circuit.

In your case the jumper MUST be removed to prevent damage.


--------------------------
A couple of other things:

1. That furnace is a 1988, so it should be inspected by a pro one of these days

2. It's dangerous (...and illegal, but maybe not in your state/municipality) to have flex gas line inside the cabinet.

3. The high temp limit is set to 200F on the existing switch -> it should be set to 180F according to the label. Someone may have tampered with it to cover up an airflow problem.

Recommended settings for the new limit switch:

Fan off-> 90F
Fan on -> 115F-140F (as per the temp rise range on the furnace with a room temperature of 70F)
Limit: 180F (do not set it any higher - if the burners cycle during a call for heat, there's an airflow problem)
 

Last edited by user 10; 02-02-13 at 10:21 PM.
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Old 02-02-13, 11:53 PM
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Thanks!

That's interesting the furnace is 1988- the house was built in 1995- I'm sure the furnace was 'new' at the time, but just not the latest model.

I will follow your settings advice... I'm guessing when the switch arrives it will have some sort of spec sheet or recommended settings with it...?
 
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Old 02-03-13, 12:08 AM
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It will come preset. You'll need to hold the round dial from spinning as you set the pointers.

Follow muggle's post......those are the correct values for your furnace.
 
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Old 02-03-13, 12:55 AM
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They stopped making natural draft (the opening at the top is called a draft hood - confirms that it's natural draft) furnaces without a damper in '92 due to efficiency regulations.

I got 1988 right off the label at the bottom -> it could mean something else.
 
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Old 02-07-13, 12:00 AM
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Guys, thank you for your help!

I got the part, installed it and am now sitting in my nice cozy house. I about had a heart attack waiting for the fan to kick on once the furnace was burning, but it went on and all is good.

Awesome forum.
 
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