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Old 01-23-2016, 11:22 AM   #21
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Originally Posted by JDZO6C5 View Post
Im going to check the intake and exhaust ports on the outside to see if there is any obstruction of air flow, but I am just contemplating the thought of just replacing the sail switch to see if that does anything. I don't really want to, since that requires pulling the entire furnace out, but obviously that may have to be my next step anyway if the intake and exhaust ports are not obstructed.
you seem to be getting lots of guesses but no answers . you are on the right track . while running on battery power the fan does not have quite the same power as when on shore power . now it's trying to push air through your vents causing back pressure and not tripping the sail switch . when you pull the front cover off you are reducing restriction of air flow and now it works fine . Remember there is only one fan motor but two squirrel cages . one is used for combustion/exhaust air the other in a separate chamber to push air over the heat exchangers and heat your unit . the only real way around this is to either add extra vents out to reduce back pressure when on battery power or leave the front cover off the furnace and allow the heated air to just come out from there making the vents/registers useless . there is no other solution to this issue.

On my unit a xlr 29hsf the vents to the furnace were useless . i now have it so the vents act as a return air and the heat is blown right out where the cover used to be . the units heats much better now and the vents act as return air now for the furnace . very little modification is needed for this .; but if you wish it to work the way it was installed you will need to add more heat vents to allow great airflow with out building back poressue when on battery power
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Old 01-23-2016, 03:48 PM   #22
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I would check your existing heating vents. I wouldn't be surprised if you've got one that's crushed or restricted.
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Old 01-23-2016, 04:46 PM   #23
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I would check your existing heating vents. I wouldn't be surprised if you've got one that's crushed or restricted.

Has to be on the intake side no?



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Old 01-24-2016, 11:08 AM   #24
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Has to be on the intake side no?
Not necessarily. The total air flow is dependent on the total flow coefficient through the system. Improving flow either upstream or downstream will help. Ever had a carburetor freeze up? That's a restriction on the intake side. Clogged muffler is a restriction on the discharge side. So opening the inlet grill reduces the inlet flow coefficient, which helps reduce the total flow coefficient. He's probably JUST a bit off with respect to picking up the sail switch. Any little bit seems to bump him over the edge and close the switch.
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Old 01-24-2016, 12:17 PM   #25
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Smile back pressure issue ?????

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Originally Posted by northstar1960 View Post
you seem to be getting lots of guesses but no answers . you are on the right track . while running on battery power the fan does not have quite the same power as when on shore power . now it's trying to push air through your vents causing back pressure and not tripping the sail switch . when you pull the front cover off you are reducing restriction of air flow and now it works fine . Remember there is only one fan motor but two squirrel cages . one is used for combustion/exhaust air the other in a separate chamber to push air over the heat exchangers and heat your unit . the only real way around this is to either add extra vents out to reduce back pressure when on battery power or leave the front cover off the furnace and allow the heated air to just come out from there making the vents/registers useless . there is no other solution to this issue.

On my unit a xlr 29hsf the vents to the furnace were useless . i now have it so the vents act as a return air and the heat is blown right out where the cover used to be . the units heats much better now and the vents act as return air now for the furnace . very little modification is needed for this .; but if you wish it to work the way it was installed you will need to add more heat vents to allow great airflow with out building back poressue when on battery power
In my case, do you think it's a back pressure issue when it is operates fine at lower altitudes (shore power and battery) but will only operated with the front cover off at 10,000 ft..... Oh..Just occurred to me ........ I have never had a opportunity to operate it on shore power at 10,000 ft. Thanks for the suggestions.
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Old 01-24-2016, 01:49 PM   #26
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In my case, do you think it's a back pressure issue when it is operates fine at lower altitudes (shore power and battery) but will only operated with the front cover off at 10,000 ft..... Oh..Just occurred to me ........ I have never had a opportunity to operate it on shore power at 10,000 ft. Thanks for the suggestions.
elevation can make a huge difference . you have to remember even with a fully charged battery the fan will not put out as much cfm as it will on shore power being supplied by the converter .the converter will put out a steady 13.8 volts . fully charged battery less then 13 volts
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Old 01-24-2016, 04:28 PM   #27
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The air's thinner at 10K feet, too, so the fan doesn't move as much air.

As I said, I suspect you're very close to the setpoint. Anything that drops it just a bit is causing you problems.

I still think the major issue is probably crushed/restricted ducting on the downstream side. Someone else had a similar issue and found duct problems.
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Old 02-01-2016, 02:48 PM   #28
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Same issue

I had the same issue and discovered the same "fix" as you while dry camping on battery only in yellowstone. Removing the plywood seat would make the furnace fire up. Putting it back together the furnace would not fire up. I think the combination of high altitude/lower oxygen definitely played into the issue, because at a lower spot earlier in the week we had no issues using battery only. No issues hooked up to electric as well. We were there at the end of July and they got a cold spell where it got down to 29 degrees around July 30! We were freezing since the heater wouldn't work properly and when it did, the low voltage alarm that is hooked up to the CO2 alarm kept beeping loudly every 30 seconds to a minute or so. I wish there was a way to turn that alarm off to say the least.
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Old 02-01-2016, 04:20 PM   #29
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Side cutters and add a switch....
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