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Old 04-09-2008, 06:56 PM   #1
encantotom
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Default my experience fixing duotherm dometic LP furnaces

Hi all,

thought i would relay my experience on fixing my 3 furnaces. I have 3 duotherm dometic 90130.006 furnaces. they are mounted under the couch up front, under the dinette seat and under the rear closet drawers. i am redoing the inside of my coach now so all the furniture is out and the first two were totally exposed. only one of the 3 worked fine, so i thought it was a fine time to learn about furnaces and fix them. i removed the front two that were easy to get at and totally disconnected them and put them on a table in my garage to work on.

i spent some time with the schematic figuring out how they worked. i found a manual online for them as well. http://bryantrv.com/docs2/docs/901.pdf the ones that were not working were intermittant for a while then consistently not working. mine have a planned 30 second delay once the thermostat turns on before the fan comes on. that is from a time delay relay in the furnace, not the contol board. then the fan turns on and gets up to speed, requireing the sail fan switch to be turned on before the control board will allow the ignitor to fire the pilot which fires the burner up. on my two not working ones, the fan would come on, then they would try to lite three times, 30 seconds apart, then stop trying and there would be no heat. on the old ones like mine, once 3 attempts were made, no more attempts to light would happen, but the fan would run forever. (i changed that on the fix)

i made a test bench by using rocker switches i wired into the unit from a car battery and a bbq propane tank with hose and adapter i put together from fittings.

please be sure to check for propane leaks on the fittings before you fire anything up. i am not very scientific, i use windex to check for bubbles....

by swapping parts on the units i have, i found the two not working units to have bad control boards. they were the orignal ones, so got lots of goof life out of them. by checking around, i found that dinosaur electronics makes an upgraded board of better quality than the old ones and are cheaper. i bought 3 new boards to replace all of them for slightly over 100 bucks apiece. http://www.dinosaurelectronics.com/Ignitor_boards.htm

they have several versions of these generic control boards that fit almost all heaters and fridges that are gas. i chose to get the upgraded one, the fan control 50 plus....it has the added feature that if after the 3 times the burner doesnt light, the control board shuts off the fan. as i said before the old ones would just keep running.

on mine furnaces, the thermostat was a ground loop and in the ground circuit. for the new control boards, it required the thermostat to be a 12v dc control look, so it required me to rewire the furnace. very simple and the instructions are included with the control boards. that is only for very specific furnaces like mine.

the new boards worked great. i did have one problem where the delay timer didnt work on one, but i discovered i had reversed the leads on the timer relay and once swapped back to the right positions, that fixed itself.

now i had a different problem. two of the units would go through the startup sequence just fine but once the burner lit, they would start howling. (later i found out that an experienced furnace guy called them "a howler") i talked to two 30 year rv furnace guys and they both said it was due to either backpressure not being on the unit since i had it out of the coach or the air mixture adjustment. one said to put the exhaust pipe on it that goes to the outside of the coach. i did that and walla, one of them stopped howling. btw, the howling only lasted for about 45 seconds as the burner was getting going. but it was loud. the other one, that didnt fix it. so, another guy said to restrict the air flow by covering the squirrel cage fan opening with apiece of cardboard. i did that and it helped but not enough. so i adjusted the air mixture that is on the front of the unit. i was cautioned that they are finicky, so not to change it very much and to do it during the burner start up. mine have adjustments from A to G on a dial. you loosen the phillips screw and slightly rotate a rod which turns a damper in the back of the unit. i adjusted mine from B+ to about C+ and that fixed it.

a few words on removing the rear furnace from the closet area. that one i had to scratch my head about. my coach is a 38'. it does not have the open bathroom, but an enclosed bathroom and shower area. directly across from that door is two doors to a closet area. in half of the closet is a built in dresser with 3 drawers. it has a counter top (all made from the same laminate the rest of the coach has). the other half of the closet is a full length one. the air return for the heater is below the bottom drawer. i removed it and the heater is in there such that without removing the top counter it is not removeable. so i removed all the screws holding the countertop on. there is a 1 1/2" black ABS pipe that is the vent pipe for the tank that runs from the tank bay through this closet up to the roof. if it wasnt for that pipe, the top would just lift off. however, that pipe goes through a hole drilled in the counter top. right next to the wall, but enough so it is not notched but a hole. so i took the silicone out and carefully rotozipped it enough to be able to slide the countertop up on the pipe to the ceiling and prop it up with a stick. not elegant, but it worked. the furnaces have a sliding exhaust pipe that requires you to slide the furnace about six inche forward to remove it. no room to do that so i took the exhaust pipe off from the outside of the coach by removing the chrome plate that houses the air intake and exhaust for the furnace. they were really stuck on the coach with the rubber butyl tape. that stuff is really gooey. you have to be careful not to bend that exterior plate, so be gentle.

sounds worse than it was. the side benefit was that i wanted to run a new coax and cat5 cable from the front tv area to the bay for a bay tv. the old coax was rg59 and not in good shape. and there was a hole in there on the floor where the sensors for the tanks had there wires coming through and then there is direct access from the closet to the wire chase that runs on the ceiling all the way up to the front of the coach. while i had the space i ran another cat5e and coax to the tank bay where the cable tv port is. to replace the older one with new.

closing them up, i put new weatherstripping i got at home depot on the bottom rails where the old ones were and on the inside of the casing and put them back together.

i had taken the external plate for the air intake and exhaust off the coach as well so i cleaned the gooey butyl rubber tape off the coach and the chrome units, got some new mud duaber screens at camping world and am ready to put them all back together.

dont know if this will help anyone, but it might.

later

tom
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Old 04-09-2008, 07:07 PM   #2
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Great post Tom. It is always beneficial to have this type information available. You are becoming an expert at interior restoration on a Newell.
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Old 04-10-2008, 05:19 AM   #3
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We'll second what Michael stated! Great information Tom. This will be very helpful to other Newell owners.


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Old 04-25-2008, 05:44 PM   #4
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update to my furnaces.....

i got them all installed back in the coach. for the flex hose for the air intake i looked all over. could order them maybe but they were pricey. they needed replacing so i continued my qwest. they are a heavy foil flex hose like a dryer vent only heavier. and they are 1 3/4" in diameter, not a standard one. ended up finding them as pre-heater hose for 5 bucks apiece at autozone. go figure.

i used the rubber butyl tape double thickness to put the exterior intake and exhaust cover on to seal to the coach. trick is to tighten every day or so after the sun allows the butyl to compress. just keep checking every few days and slightly tighten then trim with a plastic putty knife the ooze.

i got new mud dauber covers at camping world. they were cheaper than anywhere online.

i got chicken and bought a higher end propane leak dectector. the propane detector that is wired into the tank valve in the coach is only sensitive to slightly over 2000 ppm and i wanted something better to check since i did all three furnaces and this hardwired one is only in the furnace under the couch and not the other two.

i ended up buying the Extech FG100 i paid 65 bucks delivered for it. i looked quite a bit and it did what i wanted. there are cheaper ones that only go to 2000 ppm detection, but i wanted better than that.

http://www.extech.com/instrument/pro...pha/FG100.html

which goes down to 50ppm.

i checked it and have no leaks anywhere that are detectable. then yesterday i tried to test the furnaces....no luck. only because it was 85 degrees inside the coach and the thermostats would not turn the heaters on....so i got up at 3:30am this morning and went and tried them when it was 75 degrees inside. they all worked great! they had no howling and the delays worked fine and they ignited on the first try for all three of them. so am glad that is all done.

i ended up making some metal brackets to mount them to the floor of the coach. before they were loosely mounted on the floor.

btw, if you need extra rivets, i found a box spilled under the closet on the floor that were spilled those many years ago when newell built the coach. so i have OEM rivets i am will sell as collector items for ten bucks apiece. maybe it will finance some of my updates........yea right.

now i have a new electric heater from cadet to see if i can make it fit under the bed, bathroom and in the bay. of course they are not quite the same dimensions.

tom
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