Lance furnace

[fikkellin]

It seems like the furnace cycles for too short of time ...can comes on then burner comes on for a minute or two then Shuts off and the fan continues to run for a minute mostly colder air....does get up to temp
But does take a long time.... Seems like it should run for 5 minutes or longer would be better any suggestions ?

[skipbee]

I had a similar problem, we were advised to blow out the furnace after removing the outside cover and using an air compressor. I got a mess of dust and crud. All's well now. Will repeat the process next fall.

[3_tons]

I had the exact same problem as the OP described...Furnace is an Atwood 15/22...Making a field repair, the sail switch was fine...Problem was the igniter gap out of adjustment...Igniter is behind the gas valve (up high - 1 red wire) and the contact gap was found to be 1/4". I squeezed them back to the factory setting of 1/8" and all was fine again...also, check out the red wire connectors and continuity before removing igniter.

Good Luck,

3 tons

[AnEv942]

I hope were not muddying the water too much, I believe OP gained a resolve and we do not confuse by added discussion, however some comments were made that IMO should not stand without clarification or rebuttal.

No RV furnace I'm aware of burners light & run with fan off. Either enlightenment, because all I know is how much I don't know, and there may be some RV furnace that operates as Rollin described. If there is such a heater I would like to know about it. If there is not, the information needs to be countered. If it is misunderstanding of how RV furnace works then someone else might learn something. Otherwise ...

I'm seeing down the road, someone noting that their fan no longer runs while burner is on or cycles on/off WHILE burner remains lit and generating heat (though redundant safety features should not allow that). Looking for information stumbles across this thread- reads the comments that the fan cycles on & off while burner is heating box-so assumes they don't have a problem.

Im not as tactful as mkirsch, but hope the OP and anyone else with similar issue reading this thread understands why its drifted from the original post and resolve (we hope) & doesnt detract.

[okan-star]

travelnutz wrote:
mkirsch,

So true that RV furnaces do not work like Rollin described and note he reference to an automotive heater which uses engine heated water etc liquids. Not chance of fire as the liquid is around 200 degrees which is a mere fraction of burning fuel flames. We ARE talking about RV furnaces and propane burning flames as that's what this thread is about. It would be unlawful and never pass muster and there'd fire after fire if the blower fan wasn't first in RV's.

However, home furnaces can and most modern ones do work different as they have TWO fans in the furnace system. The combustion chamber blower small fan and the big blower fan to distribute the heated air. The small combustion chamber fan comes on first after the "call for heat" signal comes from the thermostat and forces any raw gas fumes out of the combustion chamber. After a preset timed delay, the gas valve opens and the igniter is activated. POOF! The burning flame heats the chamber and the plenum to a preset temp or period of preset time and then the big blower starts up to deliver the heated air. When the thermostat setting is reached, the gas valve closes and the flame goes out. The big blower fan continues until the plenum temp lowers to the preset temp (some use time) and then it shuts off.

Wood type stoves may or does have a heat activated sensor that turns on the blower after the unit's heat is sensed to be high enough.

Different animals and they require different controls and operation's sequences.

Yea its called an induction fan in a house unit but why are we confusing the subject of an rv heater that has one motor and two fans on it, one for the combustion chamber and one to blow heat
The fan has to come on first to clear the combustion chamber in case there is gas in it to avert an explosion , and stay on after for the same reason
The OP`s question was answered I think by adjusting the stat

[travelnutz]

mkirsch,

So true that RV furnaces do not work like Rollin described and note he reference to an automotive heater which uses engine heated water etc liquids. Not chance of fire as the liquid is around 200 degrees which is a mere fraction of burning fuel flames. We ARE talking about RV furnaces and propane burning flames as that's what this thread is about. It would be unlawful and never pass muster and there'd fire after fire if the blower fan wasn't first in RV's.

However, home furnaces can and most modern ones do work different as they have TWO fans in the furnace system. The combustion chamber blower small fan and the big blower fan to distribute the heated air. The small combustion chamber fan comes on first after the "call for heat" signal comes from the thermostat and forces any raw gas fumes out of the combustion chamber. After a preset timed delay, the gas valve opens and the igniter is activated. POOF! The burning flame heats the chamber and the plenum to a preset temp or period of preset time and then the big blower starts up to deliver the heated air. When the thermostat setting is reached, the gas valve closes and the flame goes out. The big blower fan continues until the plenum temp lowers to the preset temp (some use time) and then it shuts off.

Wood type stoves may or does have a heat activated sensor that turns on the blower after the unit's heat is sensed to be high enough.

Different animals and they require different controls and operation's sequences.

[mkirsch]

Rollin wrote:
Hey fikkellin, I'm sorry I didn't catch the typo can for fan. However, moving air will be cool unless it is warmed by a hot firebox or hot heater coils in a car. The fan should not come on until the firebox reaches a set temp. If the fan cycles on and off a lot when it is extremely cold while the burner keeps going then its going to take a little longer to get to t-stat set temp.

I'm going to be a little less delicate in my response and say, "No EFFING way does an RV furnace function like this!"

Air must be blowing across the heat exchanger at ALL TIMES that the burner is burning. Otherwise the heat exchanger will quickly overhead and melt. It's just made of lightweight sheet metal.

If the direct result of a meltdown isn't a burning camper, at the very least you now have wonderful carbon monoxide blowing straight into the living area. Turns the camping adventure into a one-way trip, real quick.

[Butch50]

Rollin wrote:
Hey fikkellin, I'm sorry I didn't catch the typo can for fan. However, moving air will be cool unless it is warmed by a hot firebox or hot heater coils in a car. The fan should not come on until the firebox reaches a set temp. If the fan cycles on and off a lot when it is extremely cold while the burner keeps going then its going to take a little longer to get to t-stat set temp.

Where are you coming up with your info and like stated above what type of furnace do you have? Please post your reference telling that this is the way they work.

Here is an excerpt from a web page telling how an RV furnace works. In fact my house fan comes on before the it well ignite the gas in the fire box. The furnace wants to make sure you have air flow before starting to heat up.

"•Your RV furnace operates on the 12vdc system, You do not have to be plugged in to 120v power use it.
•If your thermostat only controls the furnace and has a switch to turn the furnace on/off, switch to ON position. If your thermostat controls the furnace and the air conditioner make sure the switch is set to FURNACE.
•Set thermostat to warm temperature and furnace blower should come on after 15-30 seconds.
•Blower runs for 15-30 seconds then burner will fire up. It's normal for burner to cycle on and off.
•When proper temperature is reached the burner will cut off, blower will continue to run for a short time."

Same site

"If your furnace fan starts you can assume that the thermostat is working.

Possible problems are insufficient air flow through the furnace a bad propane valve at the furnace or a bad regulator at the propane tank.

A furnace contains an internal sail switch, that senses the air flow. If the air flow is not sufficient then the switch will prevent the furnace from igniting and the fan will run but you will get no heat. A slow motor speed could be caused by a low battery or other low voltage cause such as a bad connection in the wiring.

Low air flow could also be caused by a restriction in the ventilation system. Check to see if any heat registers are closed or blocked. Some furnaces will not tolerate even a partial closure of a heat register. .

If you have an electronic ignition check to see if the two contacts are touching or are too far apart. They should be about 1/8 apart."

This is from this web site

Here is another site telling how the RV furnace works.

Go down to the "SEQUENCE OF OPERATION OF DSI MODELS:" and read the how they work.

[AnEv942]

Rollin wrote:
Hey fikkellin, I'm sorry I didn't catch the typo can for fan. However, moving air will be cool unless it is warmed by a hot firebox or hot heater coils in a car. The fan should not come on until the firebox reaches a set temp. If the fan cycles on and off a lot when it is extremely cold while the burner keeps going then its going to take a little longer to get to t-stat set temp.

I am really curious..What brand/model of rv furnace functions like this? Its is contrary to every heater Im familiar with? The fan comes on first-stays on while heater is burning, goes off last to cool the box. Fan doesnt cycle on/off while burner is actually lit. Is this how yours operates?

The OPS problem was cycle time-which he adjusted as okan-star outlined. Hopefully issue solved.

[Rollin]

Hey fikkellin, I'm sorry I didn't catch the typo can for fan. However, moving air will be cool unless it is warmed by a hot firebox or hot heater coils in a car. The fan should not come on until the firebox reaches a set temp. If the fan cycles on and off a lot when it is extremely cold while the burner keeps going then its going to take a little longer to get to t-stat set temp.

[Butch50]

okan-star has it.

The fan has to run, unless you have a faulty sail switch, before you can get any gas flow to the burner. They don't want the burner to come on without the fan blowing.

[AnEv942]

mkirsch wrote:
The blower is running, according to the OP.

The problem is the furnace burner is only running for 2 minutes, then shutting off.

This could be one of two problems:

1. A vent is blowing hot air right on the thermostat.
2. The burner is sensing that it is getting too hot, and shutting down to prevent a heat exchanger meltdown.

If your heat exchanger is caked with dust it can prevent the efficient transfer of heat to the air being blown through by the fan.

Sorry my response was to Rollins comment (edited my post) not OPs.

[mkirsch]

The blower is running, according to the OP.

The problem is the furnace burner is only running for 2 minutes, then shutting off.

This could be one of two problems:

1. A vent is blowing hot air right on the thermostat.
2. The burner is sensing that it is getting too hot, and shutting down to prevent a heat exchanger meltdown.

If your heat exchanger is caked with dust it can prevent the efficient transfer of heat to the air being blown through by the fan.

[AnEv942]

Agreed, not knowing what heater you have but the thermostat turns on heater-
the fan/blower is what signals controls that its ok to fire burner. When tstat turns off- it turns off burner, fan continues to run to cool the box down.
Unless this operation can be verified as 'normal' If your seeing burner on and no fan running- on a typical horizontal rv furnace, I believe you have problem.

Edit: response to Rollins comment-not OP

[okan-star]

Rollin wrote:
Well, I just had to coment on this subject. Travelnutz pretty much nailed it. Heating systems for the most part are closed loop. If the abient air recirculating inside is so cold that it cools the firebox down, then the blower control will close down so that the burner can raise the firebox temp back up. When the firebox reaches a certain temp then the blower switch closes and the blower engages, as the abient temp increases so does the blower on time. When the set abient temp is reached then the burner will close and then the blower.

I don`t belive that the burner could ever be on and the blower not.
The sail switch controls the blower and keeps it running until it reaches a set temp after the burner is off, to exhaust gas on the combustion side of the heater to outside