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Old 11-19-2013, 10:12 AM   #1
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furnace short cycling , poor heat

I noticed the other night the furnace in our grey wolf was short cycling. Good hot air for about 5 mins and then the burner would cut out and only run fan and as the furnace cooled down it would relight the burner. Classic short cycle. I pulled the air return panel under the stove and the first thing I noticed was I thought the frame of the furnace itself was very warm. I pulled the access panel off the burner compartment and there is a heat overload limit right there. I was able to determine that particular limit is taking the furnace out and then cooling off and allowing the furnace to re light.


Here is the good stuff...

The burner box has provisions for up to six 4inch supply air taps to be ducted into the living space for hot air. This application is only using two. I'm suspecting that there simply is not enough air flow over the heat exchanger to allow the furnace to operate correctly with out short cycling.... I am considering trying to install at least two more taps into the living space to help achieve enough airflow across the heat exchanger to prevent the short cycling....

Any thoughts/suggestions??
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Old 11-19-2013, 10:19 AM   #2
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Originally Posted by only1stegall View Post
I noticed the other night the furnace in our grey wolf was short cycling. Good hot air for about 5 mins and then the burner would cut out and only run fan and as the furnace cooled down it would relight the burner. Classic short cycle. I pulled the air return panel under the stove and the first thing I noticed was I thought the frame of the furnace itself was very warm. I pulled the access panel off the burner compartment and there is a heat overload limit right there. I was able to determine that particular limit is taking the furnace out and then cooling off and allowing the furnace to re light.

Here is the good stuff...

The burner box has provisions for up to six 4inch supply air taps to be ducted into the living space for hot air. This application is only using two. I'm suspecting that there simply is not enough air flow over the heat exchanger to allow the furnace to operate correctly with out short cycling.... I am considering trying to install at least two more taps into the living space to help achieve enough airflow across the heat exchanger to prevent the short cycling....

Any thoughts/suggestions??
This is exactly what I did on my '12 28BH. Added another duct right by the door. It was a bit of work, but helped distribute heat better. I never had any problems with short cycling. Not sure about yours, but mine had completely exposed underbelly, so I heated with electric mostly. In my new fiver, I must use the furnace some to keep the underbelly tanks and piping heated, unless I don't plan to use water.
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Old 11-19-2013, 10:50 AM   #3
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Another thought: Do you have a bug screen in the outside intake/exhaust? The manufacturer says not to use those. That might be restricting your flow too much as well.
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Old 11-19-2013, 10:55 AM   #4
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Another thought: Do you have a bug screen in the outside intake/exhaust? The manufacturer says not to use those. That might be restricting your flow too much as well.
Actually I do..... does suburban say that or forest river?

I will try the furnace with the wasp guards off and see what happens
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Old 11-19-2013, 11:58 AM   #5
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Actually I do..... does suburban say that or forest river?
It's in the Suburban book, at least for my heater. I leave them on except when I'm going to use the heater.
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Old 11-19-2013, 12:01 PM   #6
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Originally Posted by only1stegall View Post
I noticed the other night the furnace in our grey wolf was short cycling. Good hot air for about 5 mins and then the burner would cut out and only run fan and as the furnace cooled down it would relight the burner. Classic short cycle. I pulled the air return panel under the stove and the first thing I noticed was I thought the frame of the furnace itself was very warm. I pulled the access panel off the burner compartment and there is a heat overload limit right there. I was able to determine that particular limit is taking the furnace out and then cooling off and allowing the furnace to re light.


Here is the good stuff...

The burner box has provisions for up to six 4inch supply air taps to be ducted into the living space for hot air. This application is only using two. I'm suspecting that there simply is not enough air flow over the heat exchanger to allow the furnace to operate correctly with out short cycling.... I am considering trying to install at least two more taps into the living space to help achieve enough airflow across the heat exchanger to prevent the short cycling....

Any thoughts/suggestions??
If your unit is short cycling, for the reason you stated you should put a meter on the limit to see if that is opening when it shuts down. Where is your stat located compared to a heating duct? If you turn your stat up to 80 will the unit stay on? You can also just open 1 of the area without a duct and see if that helps and if it stays on, unless you really want to add more ducts anyway. But you need to find the reason out first. How many total registers do you have in the floor 2 or do you have more in the sidewall or floors somewhere?
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Old 11-19-2013, 01:04 PM   #7
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Have had a wire hornet/wasp guard on our last 2 units and never had a problem with the furnace. Don't use them that much, but when we do, the furnaces worked fine. We normally use only the EdenPure elec. heater and if it is going to be below freezing, I just turn the furnace blower on. Had to do this for 3 nights last week. Ran the blower from about 9pm to 9am the 3 nights.
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Old 11-19-2013, 01:20 PM   #8
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If your unit is short cycling, for the reason you stated you should put a meter on the limit to see if that is opening when it shuts down. Where is your stat located compared to a heating duct? If you turn your stat up to 80 will the unit stay on? You can also just open 1 of the area without a duct and see if that helps and if it stays on, unless you really want to add more ducts anyway. But you need to find the reason out first. How many total registers do you have in the floor 2 or do you have more in the sidewall or floors somewhere?
Yes I watched the limit open with my meter.

Two registers total, as stated in original post.

Thermostat is on side wall in front of bunks, factory location.

The furnace is not cycling on the thermostat , but rather the limit as I stated before.
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Old 11-19-2013, 01:57 PM   #9
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Originally Posted by only1stegall View Post
Yes I watched the limit open with my meter.

Two registers total, as stated in original post.

Thermostat is on side wall in front of bunks, factory location.

The furnace is not cycling on the thermostat , but rather the limit as I stated before.
Strictly as an experiment, remove the limit from the furnace and try it.
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Old 11-19-2013, 04:21 PM   #10
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Yes I watched the limit open with my meter.

Two registers total, as stated in original post.

Thermostat is on side wall in front of bunks, factory location.

The furnace is not cycling on the thermostat , but rather the limit as I stated before.
Well now you need to find out if the limit is good by temp at the limit location. I find it hard to understand how a 26' unit has only two ducts in it. Not that I doubt you. I'm just not familiar with your unit and this is the first time I heard about only 2 ducts. A 4" duct will only carry about 80 cfm depending on the static pressure. Do you have a return air? I ask you that because mine did not have one when I bought it. they seemed to forgot to install it. I had to take it back to the dealer to have them cut one in. Sorry I didn't catch the part that you had a meter on the limit when it opened and broke the circuit to the valve. You might want to also call Suburban and ask what temp the high limit is set for. Or as OC said jumper it out and see if it stays on. You must be getting heat out of registers thats pretty hot to open your upper limit.
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