Propane heater cycles on & off

[dsbike]

I know this is an old thread, but there doesn't appear that anyone has come up with a diffinitive fix.

2001 Winnebago Journey 35' DP, Suburban SP-42 heater. This RV is my parents.

Our problems is as follows: When the heater is turned on at the thermostat the fan comes on for about 30 secs (normal) then the burner kicks on (normal) then after 3 min the burner kicks off but the fan continues to run to cool the heat chamber for about 90secs, then the burner kicks back on & continues to cycle like this until desired temp is reached. Not normal, when it was extremely cold this past winter it would not get the coach warm enough to ever turn off.

This is what we have done so far:
Last fall we replaced the high limit switch thinking it was turning off pwr at a low temp. No help. While the heater was out of the RV we cleaned the fan for the heater. Checked the floor plenum for any restrictions, none.

At this point it was Christmas week & did not have time for any more troubleshooting. Jan 1st my parents headed to central Fl. There they had an independant service tech come & work on it. He said the converter/inverter was bad & the heater was getting insufficient pwr. He replaced this & charged them 3X the price of the converter/inverter + $450 labor. No help, later had the old con/in checked out, operated properly. Yes he ripped them off, a story for another post. My dad replaced the propane gas regulator due to insufficient flow. They continued to use electric heater all winter until they returned to NC where we have been TSing this now.

Present: We contacted Suburban Factory Service Techs. They have been very helpful, but we still are not operating properly. Per the techs suggestions we have done the following. Measured the cold air return in side the RV, 35sqin, tech says it need to be at least 88sqin. We opened up the floor to allow more airflow, we now have 112sqin of air intake in to the heater & replaced the high limit switch again. The heater now runs for about 5min before cycling & has a bit more air coming out of the floor vents. We removed all floor registers & inspected the duct work for any restrictions, none. We ran the furnace with the registers removed, no change. We tried to measure the amp draw on the heater motor, but we did not get the desired measurement the tech told us we should, he wanted us to check the red wire, there are 3 red wires, tried them all, Could not call him back due to after closing hours, I will call tomorrow.

We removed the heater from the RV & bench tested it, the heater/burner ran continuously until we blocked off the hot air exhaust almost completely, to apprx 10sqin. At this point it finally cycled off & on. I also found a placard on the heater box that says the air intake needs to be a min of 142sqin. We closed off the air intake on the bench to simulate the present amount of opening we now have , it did not shut off the burner. I am leaning now towards adding another register or opening up one or more of the present registers to a larger size, but I don't want to cut up the floor unless I am sure this is the fix. We also checked that there is no register blowing on the t-stat to cause this to happen.

Sorry for the long post, but I wanted to avoid the replies that lead us to do what we have already done. I know several other people have had this problem, has anyone come up with a truely positive fix?

[Robs]

Would that be a SF 42 model?

[dsbike]

Yes SF42

[GaryKD]

Hi dsbike,
The bottom line is the furnace works correctly when on the bench, but not in the coach. I know the propane regulator has been changed. However, consider double checking the propane flow to the furnace. The only trouble I've had with my furnace (Suburban) is when I got a bad tank of propane. A gooey liquid (like a very light sowing machine oil) came out of the regulator. I had to change the regulator twice before I got it cleaned out. Even if all the other appliances work okay, the furnace uses propane like water going over Niagara Falls. My symptom was the same as yours.

[Robs]

On that model if the fan motor drags it will cause those symptoms and it takes 2 or 3 mins for the fan motor to warm up. To test it check the 12vcd draw when the fan motor is cold at startup and then again at 3 mins if volt draw goes up the its the fan motor.

[MrTransistor]

Hello dsbike,

My money would be on overall air flow restriction. Our Adventurer had this problem although not quite as bad and if I recall correctly, we also noticed a similar effect in the Journey. I’ve been looking through the parts, plumbing, and wiring diagrams for the 2001 Journeys and since no 35 foot is listed, I’m not sure which drawings apply. Do you have the exact model of coach? Having looked at all the drawings, I am not sure that knowing this will help since the exact location of the furnace is not shown. The inference is that it is right beside the hot water heater since that panel seems to have a small cut out in the top right corner that looks like it could be for the air intake and exhaust of the furnace. Is it just behind the right rear wheel?

There was a thread quite a while back having to do with the air flow restrictions in the Adventurer but my memory isn’t coming up with anything on the Journey. I did make an air intake cover for both units because the intake is directly above the exhaust and it was my feeling that exhaust air was being mixed with fresh air being pulled into the intake. This would have an adverse effect on combustion efficiency. After the cover was installed, the furnace ran noticeably less on both coaches. Now that I remember this, I should make one for our current coach.

With your problem, the symptoms would suggest that the burner unit is becoming too hot. That trips the high temp limit switch which shuts the propane off. As the fan after-runs to reduce the burners heat, the burner cools enough for the high temp switch to reset and the gas comes back on. This cycle repeats until the demand stops. This can be caused by inadequate air passing over the burner unit. This is caused by three things: low voltage to the fan motor (but we are talking about dead batteries i.e. 10 volts), a defective fan motor (dragging as it heats up which is detected by increasing Amp. draw), or overall air flow restriction.

As mentioned in an earlier post, restrictions can be caused by rodents or insects making a home in the ductwork. Also, clogged air filters or the worst culprit, poor ductwork design! When it comes to furnace design, more is better for duct area and Winne engineers tend to scrimp a bit. Remember that the Suburban recommendations are direct in and out areas and don’t allow for the twists and turns and long ducts running under the floor that Winne uses. That was the problem with the Adventurer. The furnace was all the way in the back so the duct was over 30 feet plus the return air was under the bed.

If the furnace worked properly at one time and has started this behavior in the last couple of years, I would suspect something is blocking the ducts somewhere. Time to drag out the inspection mirrors and flashlights? Nests can be in some really out of the way places. Keep us posted and good luck.

[Gary RVRoamer]

I'd bet on inadequate air flow through the heat exchanger too. On theworkbench, in the open air, it probably sheds enough heat to get by, but mounted in the RV the exchanger probably heats up a lot more. Can you open up another outlet duct and just lay the duct tube out on the floor temporarily to see if that stops the cycling? If it does, proceed with the mods. If not, look at the fan speed as Robs suggests.

[dsbike]

Originally Posted by MrTransistor

Hello dsbike,

My money would be on overall air flow restriction. Our Adventurer had this problem although not quite as bad and if I recall correctly, we also noticed a similar effect in the Journey. I’ve been looking through the parts, plumbing, and wiring diagrams for the 2001 Journeys and since no 35 foot is listed, I’m not sure which drawings apply. Do you have the exact model of coach? Having looked at all the drawings, I am not sure that knowing this will help since the exact location of the furnace is not shown. The inference is that it is right beside the hot water heater since that panel seems to have a small cut out in the top right corner that looks like it could be for the air intake and exhaust of the furnace. Is it just behind the right rear wheel?

There was a thread quite a while back having to do with the air flow restrictions in the Adventurer but my memory isn’t coming up with anything on the Journey. I did make an air intake cover for both units because the intake is directly above the exhaust and it was my feeling that exhaust air was being mixed with fresh air being pulled into the intake. This would have an adverse effect on combustion efficiency. After the cover was installed, the furnace ran noticeably less on both coaches. Now that I remember this, I should make one for our current coach.

With your problem, the symptoms would suggest that the burner unit is becoming too hot. That trips the high temp limit switch which shuts the propane off. As the fan after-runs to reduce the burners heat, the burner cools enough for the high temp switch to reset and the gas comes back on. This cycle repeats until the demand stops. This can be caused by inadequate air passing over the burner unit. This is caused by three things: low voltage to the fan motor (but we are talking about dead batteries i.e. 10 volts), a defective fan motor (dragging as it heats up which is detected by increasing Amp. draw), or overall air flow restriction.

As mentioned in an earlier post, restrictions can be caused by rodents or insects making a home in the ductwork. Also, clogged air filters or the worst culprit, poor ductwork design! When it comes to furnace design, more is better for duct area and Winne engineers tend to scrimp a bit. Remember that the Suburban recommendations are direct in and out areas and don’t allow for the twists and turns and long ducts running under the floor that Winne uses. That was the problem with the Adventurer. The furnace was all the way in the back so the duct was over 30 feet plus the return air was under the bed.

If the furnace worked properly at one time and has started this behavior in the last couple of years, I would suspect something is blocking the ducts somewhere. Time to drag out the inspection mirrors and flashlights? Nests can be in some really out of the way places. Keep us posted and good luck.

Mr Transitor; To answer some of your questions:
1) I was wrong on the RV size it is 36' & I believe it is a Journy DL.
2) Yes the heater unit is located on the right just behind the RR Wheels
3) The burner intake & exhaust are located with in inches of each other, yes another poor design within this whole system.
4) long inadaquete duct work causing its own restrictions.
5) My dad says this is a new situtation with the burner cycling, My mom says it has always done this since they bought the RV in 2005. Don't know, I suspect my mom is correct.
6) We have inspected the duct work & we are positive there is no FOD
7) The cold air return was definiatly to small, we increased to more than required from Suburban, 5 hot air registers require at least 88sqin, we increased to 112sqin. This made a noticable improvent in air flow through out the RV.
8) still suspected high limit switch getting hot to quickly, opened up the first hot air register from 19sqin to 54sqin. No noticable change.

I have a 2004 Coachman with a Atwood heater. Fired it up to see what it would do. It does the same thing cycles on & off, but the burner stays on for about 7mins before switching off for burner cool down. I did a web research on RV propane heaters cycling. Every RV service website I read said this is a normal condition. So the next question is, Is my parents Journey working properly or not? Maybe the burner should stay on a bit longer before it cycles if the system was ever correctly designed. I think it is working as best as it can with the poor design of the duct work & heater burner int/exh setup. I know there is one other check we can do that is to check the amp draw. I tried this but found out I did not have a Amp meter that would measure a high enough DCAmps. I may have access to one & will give it a try next week when I get a chance. I need to be able to measure 11.5 DCAmps & as of now I can only go to 10 DCAmps. If this checks out good then the fan motor is good , which I suspect to be true. They are just going to have to live with the way it operates. Which at this time it appears to be heating ok, They tend to use electric heaters for the most of the time anyways.

Thanks for all your help everyone.

[ralper]

Any forced warm air furnace fan and fire should run continously until the thermostat is satisfied. Then the fire shuts off and the fan runs until the furnace is cooled off. Your ducting is not allowing sufficient air flow to remove the heat in the furnace and thus keep the fire on continuously. You proved this with your bench test. A larger return air grille and another heat outlet solved that problem for me.

Ralph

[Gary RVRoamer]

If the burner cycles off and the fan continues to run and then the burner comes back on, then the heat exchanger was overheated and that off/on cycle was due to the high limit switch. Except for a high limit cutout, it is as ralper says - the burner should stay on until the t-stat is satisfied. I too think your bench test has proved it is an air flow problem.

[Paul R. Haller]

No one to this point mentioned the batteries. If low voltage exists at the furnace the fan will run slower causing less air to cool the heat exchanger. check battery voltage first. maybe just a new battery will solve the furnace problem.
-Paul R. Haller-.