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10-17-2022, 07:51 AM
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#61
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Weatherman1
First off, the short cycling is the burner?
Have they checked the temperature difference between the inlet and outlet and compared that with the burner output?
Yes propane runs at 11.5" W.C.!
We were in arizona and had no problem with our furnace due to altitude.
If they find the delta T too high that would indicate low airflow which could be a kinked flex hose leading to the outlet.
If the delta T is normal then I would suspect the following;
Thermostat that cycles the burner may need to be changed (likely is unadjustable)
Delta T should not be more than 60 degrees i.e. 70 at the retun grill and 130 at the outlet max
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It is the burner that short cycles. The fan continues to run. I don't know if temps have been checked nor I am sure how to do it. I appreciate the input.
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10-17-2022, 02:38 PM
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#62
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Senior Member
Join Date: Jul 2019
Location: Hampstead
Posts: 131
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sorrry for the error the propane at the burner should be 10.5" water column not 11.5
I have been in the HVAC service for over 40 years and I am also an engineer.
Short cycling of the burner can only be a couple of things, not enough airflow or a defective burner limit switch.
Take a digital meat thermometer at the inlet while it is running and at the closest outlet to measure the temperature difference then tell me what the burner output is rated at or model # of the heater
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10-17-2022, 04:31 PM
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#63
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Senior Member
Join Date: Apr 2019
Location: Northern, Ontario
Posts: 110
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Weatherman1
Thanks for sharing your knowledge
It's people like you that makes this forum great.
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10-17-2022, 05:27 PM
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#64
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Weatherman1
sorrry for the error the propane at the burner should be 10.5" water column not 11.5
I have been in the HVAC service for over 40 years and I am also an engineer.
Short cycling of the burner can only be a couple of things, not enough airflow or a defective burner limit switch.
Take a digital meat thermometer at the inlet while it is running and at the closest outlet to measure the temperature difference then tell me what the burner output is rated at or model # of the heater
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Thx. i will try and do in the next couple of days and get the data posted.
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10-18-2022, 04:40 AM
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#65
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Senior Member
Join Date: Jul 2019
Location: Hampstead
Posts: 131
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Your welcome!
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10-18-2022, 10:46 AM
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#66
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Junior Member
Join Date: Jul 2020
Location: Stoneycreek
Posts: 23
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I have a funace under my jackknife couch as well . And we had to warm up the trailer one night so i turned it on heat..furn came on ran a bit and shut off..continued like that all night..so with futher investigation i realized i had a tool box on the back bumper in front of the exhaust ..it was pastic and actually started to melt..opps..so after removing it the furnace worked perfect..so as other have said about venting etc.. make sure nothing resticting exhaust vent..good luck
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10-19-2022, 07:01 AM
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#67
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Jayv
I have a funace under my jackknife couch as well . And we had to warm up the trailer one night so i turned it on heat..furn came on ran a bit and shut off..continued like that all night..so with futher investigation i realized i had a tool box on the back bumper in front of the exhaust ..it was pastic and actually started to melt..opps..so after removing it the furnace worked perfect..so as other have said about venting etc.. make sure nothing resticting exhaust vent..good luck
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On my unit the furnace vents straight out the side of the trailer. Nothing obstructing the outflow which is very short.
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10-19-2022, 07:55 AM
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#68
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Site Team
Join Date: Jan 2011
Location: James Island, SC
Posts: 22,852
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Dirt daubers love to build nests up in those vents.
__________________
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Can't find what you're looking on JOF? Try Jayco Owners Forum Custom Google Search
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10-19-2022, 08:16 AM
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#69
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by norty1
Dirt daubers love to build nests up in those vents.
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OK, I'll check the exhaust duct today.
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10-19-2022, 10:43 AM
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#70
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by norty1
Dirt daubers love to build nests up in those vents.
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My exhaust duct appears clear.
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10-19-2022, 10:56 AM
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#71
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Weatherman1
sorrry for the error the propane at the burner should be 10.5" water column not 11.5
I have been in the HVAC service for over 40 years and I am also an engineer.
Short cycling of the burner can only be a couple of things, not enough airflow or a defective burner limit switch.
Take a digital meat thermometer at the inlet while it is running and at the closest outlet to measure the temperature difference then tell me what the burner output is rated at or model # of the heater
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OK. so today I tested it as u suggested. The temp near the air intake started at 48 and went up to 54 over the 1/2 hr I did the testing. I have 4 heater vents. The nearest is in the bedroom. It maxed out at 105 at the ending of the testing. 99 was max initially, but the burner was continually short cycling. The 2nd closest vent is the front one in the living/kitchen/dining area. It has poor air flow w/ a max temp of 77. The rear one in that area maxed at 108. The bathroom located the farthest from the furnace maxed at 105. It's a DF series furnace, but I can't see a model # and won't be able to get that till the furnace is pulled next wk. Does this help?
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10-20-2022, 06:29 PM
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#72
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Moderator Emeritus
Join Date: Apr 2011
Location: Michigan
Posts: 9,424
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Doctor Chuck,
For future reference, the following info may be helpful:
Referencing my prior post #58, my 2018 24RBS has the same floorplan as your 2020 248RBSW, and my furnace is an Atwood (Dometic) model # AFMD20121 (20,000 BTU input/15,200 BTU output).
After incorporating my furnace return air modifications, I recorded the following floor heat vent temperature ranges (multiple readings): Bedroom 110-126, Living Room (near sofa) 120-136, Kitchen (near Entertainment Center) 119-140, and Bathroom 124-138.
In my case the bedroom and bathroom heat vents provided a 'tad' more air flow than the other two heat vents.
I "believe" that Dometic at some point after acquiring Atwood changed the "AF" furnace designation to "DF" ....., "if" that's the case and you confirm that your furnace model is DFMD20121, the following Dometic "DF" series furnace manual may be helpful:
https://www.dometic.com/assets/14/52...1_01_81452.pdf
Bob 
__________________
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)
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10-21-2022, 09:43 AM
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#73
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Rustic Eagle
Doctor Chuck,
For future reference, the following info may be helpful:
Referencing my prior post #58, my 2018 24RBS has the same floorplan as your 2020 248RBSW, and my furnace is an Atwood (Dometic) model # AFMD20121 (20,000 BTU input/15,200 BTU output).
After incorporating my furnace return air modifications, I recorded the following floor heat vent temperature ranges (multiple readings): Bedroom 110-126, Living Room (near sofa) 120-136, Kitchen (near Entertainment Center) 119-140, and Bathroom 124-138.
In my case the bedroom and bathroom heat vents provided a 'tad' more air flow than the other two heat vents.
I "believe" that Dometic at some point after acquiring Atwood changed the "AF" furnace designation to "DF" ....., "if" that's the case and you confirm that your furnace model is DFMD20121, the following Dometic "DF" series furnace manual may be helpful:
https://www.dometic.com/assets/14/52...1_01_81452.pdf
Bob |
Appreciate the info. Your temps run much higher than what I'm getting. And I do have the manual.
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11-10-2022, 09:05 PM
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#74
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Senior Member
Join Date: Sep 2015
Location: Mexico Beach
Posts: 2,196
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Mine started short cycling which has nothing to do with the sail switch. Fan ran but burner cycled which is the overheat switch. I removed heater took it apart and found nothing dirty or clogged. Reinstalled and it runs fine. I hate when things fix themselves. My ducting was fine so if it comes back again it will be a circuit board and overheat sensor change out. If your ducting is fine and heater clean then CB or overheat sensor are bad. Sail switch will shut the entire heater off ( no fan). When it is on are you getting good air flow from all your vents?
__________________
2024 Greyhawk 30Z
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11-11-2022, 05:50 AM
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#75
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Senior Member
Join Date: Jul 2019
Location: Hampstead
Posts: 131
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Quote:
Originally Posted by Doctor Chuck
OK. so today I tested it as u suggested. The temp near the air intake started at 48 and went up to 54 over the 1/2 hr I did the testing. I have 4 heater vents. The nearest is in the bedroom. It maxed out at 105 at the ending of the testing. 99 was max initially, but the burner was continually short cycling. The 2nd closest vent is the front one in the living/kitchen/dining area. It has poor air flow w/ a max temp of 77. The rear one in that area maxed at 108. The bathroom located the farthest from the furnace maxed at 105. It's a DF series furnace, but I can't see a model # and won't be able to get that till the furnace is pulled next wk. Does this help?
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That would put the airflow around 360 CFM which is well within tolerance which
would indicate to me that the limit switch is defective and cycling the burner too often
Weatherman
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11-11-2022, 07:35 AM
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#76
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by Weatherman1
That would put the airflow around 360 CFM which is well within tolerance which
would indicate to me that the limit switch is defective and cycling the burner too often
Weatherman
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Appreciate the thought. Picking up the trailer today from the service center. It's been there 3 wks. The manager says my ducts are clear and they replaced the high limit switch. I'm concerned that doesn't explain why I'm not getting any significant air flow from one floor vent. But if the short cycling the burner is fixed, I will be very happy. This is 4th time in the shop for this problem that has been present since we bought this new trailer. I will update once I get a chance to test the unit over the next few days.
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11-11-2022, 08:18 AM
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#77
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Senior Member
Join Date: Jun 2013
Location: McKean, PA
Posts: 1,073
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Ask the dealer how they determined that the ducts were clear. They really need to look down the length of the duct work from the inside, not just pull the covers off. They sell some snake cameras for cell phones that will let you look in the ducts.
__________________
2011 Skylark 21FKV
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11-11-2022, 08:21 AM
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#78
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Quote:
Originally Posted by us71na
Ask the dealer how they determined that the ducts were clear. They really need to look down the length of the duct work from the inside, not just pull the covers off. They sell some snake cameras for cell phones that will let you look in the ducts. |
Appreciate the advice. Will ask them today when I get there today.
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11-11-2022, 09:22 AM
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#79
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Senior Member
Join Date: Oct 2022
Location: Central
Posts: 195
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Quote:
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They sell some snake cameras for cell phones that will let you look in the ducts.
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They're endoscopes. I have one and paid about $40, several years ago. I've used it to borescope some engines and the inside of the frame on my Jeep Wrangler.
It connected to my android phone. I don't see how it would connect to my Iphone.
You can buy one with a screen attached. Depstech is the brand I have. I have no experience with other brands.
https://www.amazon.com/dp/B094XGX6GQ...T1zcF9kZXRhaWw
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11-15-2022, 09:36 AM
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#80
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Member
Join Date: May 2022
Location: Lakeside
Posts: 34
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Heater fixed, I think and hope
Just got back to 6500' after picking the TT up from Jayco service center. 3rd time in there for the short cycling problem. They put a camera in all the vents and said they were clear. They finally replaced the high limit switch. Not sure what else they might have done. The furnace seems to be burning not as hot as prior, and is not short cycling. I still don't get good heat from the vent near the heater in the main area, but the unit seems to heat up OK. Camping season over for us now till spring. I want to thank everyone who responded to this post. I shared the info with the service center and I suspect that's why they finally replaced the high limit switch.
Special thanks to Weatherman1 for the continued f/u through all this.
And to Rustic Eagle for sharing the mods you made.
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