Atwood Furnace
I'm a little frustrated with my Atwood furnace. I have a 2018 5th wheel that I bought at the RV show in Sacramento. I hit the road to Arizona and almost immediately had trouble with the furnace. Fo...
Forum Discussion
jbrack wrote:starcraft69 wrote:Old-Biscuit wrote:
Burner cycling on then off/back on/off is called 'limiting' which is when the airflow has been restricted and heat exchanger high temp limit switch is opening (too hot) then fan continues to run so temp drops...high temp limit switch closes and burner lights back off
You have something obstructing/blocking either the furnace discharge air flow OR the return air to furnace
Could be closed/blocked register, could be crushed ductwork, could be how/where stuff is stored
Fan runs cause high temp limit switch opened.burner keeps firing back off cause thermostat temp set point has not been met....high temp limit switch controlling burner shutting down/relighting
Listen to this man! This is the correct answer.
This makes the most sense to me...and has been suggested to me before but none of the mechanics who have looked at the furnace have investigated this. None of my inside vent are blocked or restricted. I can see most of the ductwork from inside the belly but cant see the duct that feeds the one floor vent in the extreme rear of the coach. My next question is...if I continue to operate the furnace in this on/off fluctuating mode, will it cause any damage?
YES!
Continued operation where high limit switch is 'controlling' the burner cycle can result in damage to the HEAT EXCHANGER.....cracks/warping---gasket leaks. That then results in CO Leakage into the INSIDE of RV,
CO is the 'silent killer'.
Every RV Furnace has a 'minimum ducting' requirements AND Return air requirements.
4" flex duct = 12 sq/ft (2" duct is NOT 1/2 of 4"---only 2 sq/inch)
16K/20K btu furnace---minimum 24 sq/inch (2 ducts)
25K/31K btu furnace---minimum 36 sq/inch (3 ducts)
35K/40K btu furnace---minimum 48 sq/inch (4 ducts)
Return Air......respectively
33 sq/inches, 65 sq/inches & 80 sq/inches
Furnace overfiring is another means of high limit switch cycling.
LP System pressure set too high will cause overfiring.
LP System should be set to 11"WC with at least 50% of propane appliances in service.
And then there is Thermostat Location
Does a register blow towards thermostat?
Is warm air coming thru hole where wires to thermostat exit the wall?
