furnace sail switch

[Brian B-P]

Originally Posted by cpaharley2008

That does not make sense when the source of combustion is from outside air one would think that blocking the outside source would be the purpose of a sail switch, inside loop means nothing to the proper functioning.

The inside air blower and the combustion air blower are driven by the same motor, so if one is turning the other one is, too, so if any specific design puts the sail switch in the cabin air loop it is still functional.

[alanmalk]

Originally Posted by Donna D.

I understand how crud or fluff or fuzz would prevent a sail switch from operating correctly. What I don't understand is how 'cabin air' affects the switch. It doesn't work off a sensor or thermostat. So why does it need 'air'? I think I need to go back to school It almost sounds like it works on some sort of air pressure (barometer), like you'd experience in general weather.

It needs moving air, which in fact is under (modest) pressure from the fan. From the previous comments it sounds like some furnaces have the switch in the combustion air flow, others have it in the cabin air flow (the air that will be heated and returned to the cabin). The sail switch is the sensor that tells the electronics that the air is moving correctly. A barometer could be used in place of the sail switch, but it would be ultra-fragile and expensive.
--
Alan

[rubicon327]

Originally Posted by alanmalk

A barometer could be used in place of the sail switch, but it would be ultra-fragile and expensive.

Many home furnaces use differential pressure switches instead of sail switches as a proxy for flow. It seems to me if Dometic wanted to they could easily incorporate that style of sensor into their furnaces and accomplish the same safety sequences.

[gbaglo]

Originally Posted by rubicon327

Many home furnaces use differential pressure switches instead of sail switches as a proxy for flow.

What happens when you go from sea level to 9,600 feet? Is a differential pressure switch set when the furnace is installed in a house that stays put?

[Rossue]

Originally Posted by gbaglo

What happens when you go from sea level to 9,600 feet?

In some people it is a bad case of vertigo.

[sclifrickson]

Originally Posted by gbaglo

What happens when you go from sea level to 9,600 feet? Is a differential pressure switch set when the furnace is installed in a house that stays put?

I’d imagine that a pressure differential exists with a properly functioning blower regardless of altitude. Does a fan only operate at a factory preset altitude?

[gbaglo]

Originally Posted by sclifrickson

I’d imagine that a pressure differential exists with a properly functioning blower regardless of altitude. Does a fan only operate at a factory preset altitude?

All I know is that making rice at sea level is different than making rice at 9,600 feet and that the recipe for many foods requires adjusting depending on altitude. I only ask if a pressure differential switch would be affected because I have a bad altitude.

[sclifrickson]

Originally Posted by gbaglo

All I know is that making rice at sea level is different than making rice at 9,600 feet and that the recipe for many foods requires adjusting depending on altitude. I only ask if a pressure differential switch would be affected because I have a bad altitude.

Touché [emoji38]

[Brian B-P]

Originally Posted by gbaglo

What happens when you go from sea level to 9,600 feet? Is a differential pressure switch set when the furnace is installed in a house that stays put?

Because it measures is the difference in pressure between before and after the blower, the absolute or barometric pressure (or altitude) doesn't matter.

My guess is that

• the differential pressure in these furnaces is low, and
• a differential pressure switch is probably more expensive than a sail switch.

... but that's only my guess at the reasons for the use of this device which is annoyingly problematic (but trouble free in my older Atwood furnaces).

[steve dunham]

The furnace requires a positive proof of air flow . That flow of air is used to purge the combustion chamber of the furnace . Since there is only one fan motor that single motor is used for purging and moving air into the room . Positive proof of air flow is accomplished with a sail switch or a differential pressure switch or a speed sensor on the fan blade . Like all heating safeties it cannot be dependent on a related signal IE You cannot assume that if the blower motor is getting power it’s working because the motor could be bad , fan blade could be bad or loose on motor shaft or the fan belt is broken .
The furnace control circuit is designed so that the sail switch has to change states in order to cycle If the sail switch gets stuck in the closed position the furnace will lock out after it’s cycle is completed . It is set up to be self checking
Once the sail switch gets stuck in one position it’s all over until you remove the obstruction

[suncoastdancers]

I have attached an assembly drawing of the AFSAD12 Hydro flame furnace noting the location of sail switch (part 23) inside the blower assembly. It appears to be facing the combustion scroll wheel (part 9) and is pushed back when the motor is running, closing and completing the circuit. I assume that the dust bunnies have been collecting behind the paddle, preventing the switch from closing. Not surprising, given that the back of the sail is in the perfect location to scoop up any debris thrown off by the fan.

A drawing of another Hydro flame model shows a different style sail switch located on the cabin-side of the blower. The video posted by Rease shows this model.

I wonder which model is current - the model with the sail switch on the cabin side or the model with the switch on the combustion side?

Any thoughts on how to prevent this buildup?

[Perry Butler]

Originally Posted by suncoastdancers

I have attached an assembly drawing of the AFSAD12 Hydro flame furnace noting the location of sail switch (part 23) inside the blower assembly. It appears to be facing the combustion scroll wheel (part 9) and is pushed back when the motor is running, closing and completing the circuit. I assume that the dust bunnies have been collecting behind the paddle, preventing the switch from closing. Not surprising, given that the back of the sail is in the perfect location to scoop up any debris thrown off by the fan.

A drawing of an earlier Hydro flame model shows a different style sail switch located on the cabin-side of the blower.

Any thoughts on how to prevent this buildup?

Thanks for the blower assembly pdf!

It appears to me, from the diagram you provided, the sail switch is in the hot air portion of the furnace, not in the combustion air portion. Facing the furnace from the outside, the diagram shows the hot air fan on the left and the combustion air fan on the right. My 2018 sail switch is on the left also. Therefore we will be adding a thin filter to the back of the inlet air grill in the camper (hope this makes sense?).

However, if I'm wrong (that wouldn't be the first time) the filter I and others are considering would be rather worthless.



Enjoy,

Perry

[suncoastdancers]

Originally Posted by Perryb67

Thanks for the blower assembly pdf!

It appears to me, from the diagram you provided, the sail switch is in the hot air portion of the furnace, not in the combustion air portion. Facing the furnace from the outside, the diagram shows the hot air fan on the left and the combustion air fan on the right. My 2018 sail switch is on the left also. Therefore we will be adding a thin filter to the back of the inlet air grill in the camper (hope this makes sense?).

However, if I'm wrong (that wouldn't be the first time) the filter I and others are considering would be rather worthless.



Enjoy,

Perry

Thanks for your help. I am trying to understand which model is current. My furnace is a late 2017. I would have to pull it out to tell. By the looks of it, and reviewing Rease's videos again, the sail switch is on the cabin side on the newer model.

You would not happen to know the part number for the sail switch off-hand??

[padlin]

Don't the new models as discussed here have a black plastic grill on them as opposed to the tanish metal grill on the older style like mine?

[sclifrickson]

Originally Posted by suncoastdancers

My furnace is a late 2017. I would have to pull it out to tell. By the looks of it, and reviewing Rease's videos again, the sail switch is on the cabin side on the newer model.

There should be a large sticker inside one of your cabinets that lists make and model for all appliances installed by ETI, including the furnace. Should look like this:

As you can see, our 19, manufactured in July 2017 was fitted with the Atwood AFSAD12. I am still unclear whether our sail switch is in the combustion or cabin airway, although I did preemptively add a cabin grill air filter, even though we’ve never had any sail switch issues.

[bdornbush]

Originally Posted by sclifrickson

As you can see, our 19, manufactured in July 2017 was fitted with the Atwood AFSAD12.

I asked Atwood about this and was told that it depends on the serial number of the furnace. Apparently, there were changes made within the same model number. And my model number is actually AFSAD12121 and that suffix is not shown on the listing inside the trailer. I learned later that the 121 suffix indicates that there is no external access panel.

"Thank you for contacting Dometic, to determine which sail switch you need we now go by the serial #, I’m sending you pictures of the sail switches can you please identify which one you need? "

I have attached the photo sent by Dometic.

[Tam2004]

Originally Posted by steve dunham

Dometic’s furnishing of a free sail switch does little to solve the real issue .

This is a design flaw and throwing parts at it just pushes the problem down the road just past the warranty period .

MY RANT: I so agree that putting in new parts doesn't necessarily work if the furnace is bad from the start. After we recorded our horrible experience with the furnace right after we picked it up (we were headed to Colorado to visit our 99 year old Aunt and have a long anticipated 4 week journey) it just gave us ongoing trouble. You may go and see our agonizing record - but it was only after we got home from our (cold) trip that our local trailer people called foul on Dometic and got us a new furnace. THE NEW ONE WORKS LIKE A GEM!!! We are in our 4th week of travel and it is perfect. I know that it SHOULD be true that putting in new parts will make it like new, but the Dometic staff person at one point did kind of slip and say "some did have issues". So, go ahead and try changing out the parts if you like - but after all of our huge efforts and many calls and many shops on our trip -- it took getting a new one to fix the problems. I appreciate all the advice on how they might not work at altitude or it was the this part or that part or maybe it was fluff in the sail switch (that rumor I think started with us finding fluff - but damn it - that didn't fix it). The good thing is that we find this furnace perfect now and we did learn how to respectfully tap the thermostat to not cause it issues (it compresses the foam underneath) and to remember to have the auto on - not low or high fan - when wanting to use the furnace or air conditioner. So I hope this will keep going on past our 4 weeks and for years like all the other trailer furnaces in the past did. Our refrigerator is indeed wonderful, BTW.

[steve dunham]

Originally Posted by Tam2004

MY RANT: I so agree that putting in new parts doesn't necessarily work if the furnace is bad from the start. After we recorded our horrible experience with the furnace right after we picked it up (we were headed to Colorado to visit our 99 year old Aunt and have a long anticipated 4 week journey) it just gave us ongoing trouble. You may go and see our agonizing record - but it was only after we got home from our (cold) trip that our local trailer people called foul on Dometic and got us a new furnace. THE NEW ONE WORKS LIKE A GEM!!! We are in our 4th week of travel and it is perfect. I know that it SHOULD be true that putting in new parts will make it like new, but the Dometic staff person at one point did kind of slip and say "some did have issues". So, go ahead and try changing out the parts if you like - but after all of our huge efforts and many calls and many shops on our trip -- it took getting a new one to fix the problems. I appreciate all the advice on how they might not work at altitude or it was the this part or that part or maybe it was fluff in the sail switch (that rumor I think started with us finding fluff - but damn it - that didn't fix it). The good thing is that we find this furnace perfect now and we did learn how to respectfully tap the thermostat to not cause it issues (it compresses the foam underneath) and to remember to have the auto on - not low or high fan - when wanting to use the furnace or air conditioner. So I hope this will keep going on past our 4 weeks and for years like all the other trailer furnaces in the past did. Our refrigerator is indeed wonderful, BTW.

The closest authorized Dometic Service Center is almost 200 miles from our home
The service center is part of a trailer dealership that sells new trailers . The option I was given was to haul my trailer down to their dealership / service center , drop it off , go home and wait .Since I didn’t buy my trailer from the dealership I go to the bottom of their repair list (Trailers bought at the dealership get repaired first.) He would not give me a time frame , could be 3 days , could be 3 months .
I decided to opt out , so much for the Dometic warranty
I was not enthralled with the idea of having my trailer tied up for only God knows how long , and possibly losing a whole Summer of camping .
We had a Dometic service center in our area a while back but he dropped out of the program due to issues with Dometic (Read Money )

If it wasn’t so far to Chilliwack ,I would bring my trailer back
to ETI and pay them to change out the furnace with the new style with the outside access panel .

[suncoastdancers]

Originally Posted by bdornbush

I asked Atwood about this and was told that it depends on the serial number of the furnace. Apparently, there were changes made within the same model number. And my model number is actually AFSAD12121 and that suffix is not shown on the listing inside the trailer. I learned later that the 121 suffix indicates that there is no external access panel.

"Thank you for contacting Dometic, to determine which sail switch you need we now go by the serial #, I’m sending you pictures of the sail switches can you please identify which one you need? "

I have attached the photo sent by Dometic.

Thanks for your help.

Looks like I am blessed with the older model. The serial number starts with 607.

While rummaging about, I did find a lot of sawdust and loose wood shavings in the cabinet housing the furnace. I vacuumed these out of course. If you are following this post Rease, perhaps something to watch during assembly.

Paul

[rubicon327]

Originally Posted by gbaglo

What happens when you go from sea level to 9,600 feet? Is a differential pressure switch set when the furnace is installed in a house that stays put?

Originally Posted by sclifrickson

I’d imagine that a pressure differential exists with a properly functioning blower regardless of altitude. Does a fan only operate at a factory preset altitude?

Good question. Since it is a differential it shouldn’t matter but all switches may not be created equal. Some online literature indicates that in some home furnaces they need to be changed above 7000’, but in practice it sounds like most typically work fine and are not changed until above 10,000’. As a practical matter in the US this issue doesn’t impact too many people. The bottom line is that if Dometic engineers wanted to develop a better air proving device on their furnaces they certainly could.