Suburban Furnace (Dynatrail NT30, 1985 model) Won't Start

[William Briggs]

Last week, I thought I'd test the furnace before wintertime. I flipped on the wall thermostat, turned the temp lever up. After a few seconds, I heard a click in the furnace, then nothing more happened. Tried several times, same thing.

 

Researched the problem on the internet. Learned that the most likely culprit was a bad "time-delay relay." Following the instructions on the internet, I slid the furnace out, jumped across the relay, and the furnace worked. So I ordered a new relay online. Should have been easy enough. The new relay arrived yesterday, so this morning I pulled out the furnace, replaced the relay. But the furnace is still doing the same thing ... turn on the thermostat, wait a few seconds, hear the click, but nothing more.

 

As I understand it, the thermostat needs heat, so it sends current to the furnace relay. The relay (time-delay) then turns on the fan after 25 seconds. Once the fan turns on, it trips a "sail switch" and the furnace fires up. But I can't get the fan to come on without jumping a wire across the relay.

 

Has anyone experienced this problem? I'll be carrying the furnace to the RV repair shop next week, unless someone has an idea.

 

Best regards,

 

Billy

[John "T" Nordhoff]

  These things are tough over the net, if there with a 12 VDC test lamp and continuity checker it would be easier. Okay, remember there are two sides to that time relay, the control side input would get voltage when the t stat makes up (sounds like that much is working) with the other end of that control side coil going to ground...........The t stat makes up and sends voltage to the relay control coil input, current flows through the control coil to ground.

 

 Nowwwwwwww after a delay the other contactor side of the relay closes a set of contacts AND I THINK THATS THE CLICK YOU HEAR (i.e. the relay is working). The input side of that side (the normally open contactor) of the relay needs 12 volts present so when the contacts close (after the delay and the clik you hear) voltage gets to the fan via the closed relay contacts.

 

  I WONDER IF THE PROBLEM IS THERES NO 12 VDC PRESENT AT THE INPUT SIDE OF THE CONTACTOR PORTION OF THE RELAY????????? The other side works, you hear the click, the click is the contactor closing, BUTTTTTTTTT THERES NO VOLTAGE SOURCE ON THE INPUT TO SEND TO THE FAN

 

 I cant say where that 12 vdc comes from, maybe a wire is broke or a fuze is blown etc BUT I CAN SAY THERE MUST BE 12 VDC PRESENT AT ALL TIMES ON THE INPUT SIDE OF THE CONTACTOR so when it closes that 12 vdc feeds the fan. Then the fan turns,,,,,,the sail switch makes up,,,,,,,,the ignitor starts firing spark,,,,,the gas valve opens (ifffffffff shes sparking and iffffffffff sail switch closes)

 

  Get your voltmeter on the input side of the contactor (thats the output side NOT the control side from t stat to ground) and look for 12 VDC, if its not there even if the relay works n clicks theres no 12 vdc to the fan

 

  WHEW I need a nother cup of coffe now lol

 

  Ol John T  Tooooooooo long retired electrical engineer n rusty as an old nail

 

[William Briggs]

John,

 

Thanks so much for your reply! I put the meter on it today, and traced 13 volts through the circuit. The time delay relay, after 25 seconds, is pushing 13 volts through. So the time-delay relay is working as designed.

 

I'm in Oklahoma so I won't need the furnace for a month or so. I'll think about it for a day or two and, if I don't get the answer, the RV shop is 2 miles down the road. At this point, I can't get the fan motor to come on, even by jumping across the time-delay relay. I presume the motor starts with a capacitor. How do they act when they are dying?

 

We accountants should leave stuff like this to you mechanical types.

 

I sincerely appreciate the help. I had to read your reply a couple of times, but I figured out exactly what you were saying about the 2nd 12-volt wire. I did test that circuit today and it's working as designed.

[John "T" Nordhoff]

  That DC Repulsion Motor DOES NOT use any capacitor to start, those are used for AC motor starting. (some small capacitors can be used for radio inteference suppression).  Okay, its the delay relay that powers the fan so if its working (and all the rest and wiring is okay???) but even if 12 VDC is applied direct to the fan it dont turn MUST BE A BAD FAN, but it seems strange since you say it did work before with a jump??? Usually when a fan goes bad its the bearings that go dry first and they start squealing when first started especially when its colddddddd. I know you say you jumped the relay but Id still suspect a wiring or some other problem BEFORE the fan itself.  The only way to know is run a hot 12 VDC DIRECT to the fan with a ground and if she still dont turn then yes finally its a bad fan. Looks like this is all we can do over the net so if she dont work its off to the RV shop, but if you remove the furnace yourself and drag it into the shop even if it needs a fan youre not looking at all that much money.

 

  Best wishes

 

  John "T" in Indiana    Not too long before we head to Florida woooooo hoooooo

 

  http://travel.webshots.com/album/576959192LrNXNi

[William Briggs]

John, your cheerleading is helping a lot. I might try once again to trace the circuits.

 

Thanks!

 

Billy

[brian moorcroft]

HI william did you get your furance working I had the same thing with mine the fan was stuck .I got I long thin stick and push the fan round till it came free agian but my furnace had not been use for 16 years but mit be the same thing mate. but it work fine now

[William Briggs]

Thanks for responding, Brian. John did his best to try to help me long-distance; I appreciate him very much. The fan is rotating freely; I checked that. At this point, the furnace is in the back of my Dodge. Tomorrow, it's going to the furnace-hospital.

 

I enjoyed looking at the pics you posted. I have considered repainting my Pace Arrow to a more-modern color. I was pleased to see your painting work. With the addition of a few modern graphics, your motorhome will look much more modern than mine -- although, if I remember correctly, yours is several years older.

 

However, outside of the ugly beige color, the body and the finish of my Pace Arrow are in reasonably good shape. (It was garage-kept for many years.) Therefore, I intend to keep the original exterior colors, for the time being. Piece by piece, I'm working off the oxidation with rubbing compound, then applying a heavy coat of paste wax.

 

I will be interested in reading more about your restoration work, and seeing the pictures.

 

Happy trails,

 

Billy

[William Briggs]

Finally carried the furnace to the shop. According to the mechanic, the motor was seizing. (Yeah, John, I don't understand it, either.) Of course, he couldn't find the exact replacement, but found one which he made to fit. He replaced the sail switch while he had the furnace apart.

 

$400 and one month later, the furnace works beautifully. Does a great job! But it seems that mechanic is awfully proud of his work.

 

John, thanks again for all your patient help! Hopefully, I can do a favor for you sometime.

[John "T" Nordhoff]

   WOW  William, youre right, Id say that dude is indeed proud of his work!!! Especially considering Flea Bay has Suburban Furnace Motors from $85 to $150 or you can buy a whole freakin new furnace in the $400 to $600 price range. Buttttttttt it works now and thats worth a bunch plus the peace of mind. As an old buddy used to say, A body soon forgets what he had to pay for repairs if the dern thing works.

 

  Ive owned several used RV's over the years and keeping furnaces and hot water heaters n fridges all working is an ongoing job. However good preventive maintenance like cleaning and purging and blowing out the air inlet and flu pipe tubes and passages and frequent exercising of units (letting things set unused for months is hard on them) sure helps. As an example a buddy last winter comes running over to me "My fridge wont light on gas" so I open the inspection plate beside where the burner is and theres a hugeeeeeeeee hunk of soft powdery carbon soot that was shorting out the peizo igniter from sparking to light the burner flame. I say "have you ever took your air blow gun and cleaned out all that soot n rust n carbon in the burner and flu pipe" he responds "never have"  well DUHHHHHHHHHHH He asks if I have ever cleaned mine I respond "TWICE A YEAR"

 

  But hey all that poor maintenance Im always railing against makes for good work for RV service techs and the country needs jobs right?? If all were tight as me the country would be in even worse shape I reckon........DO YOUR PART TO CREATE JOBS AND NEW PARTS SALES YALL,,,,,,,DONT PULL REGULAR MAINTENANCE !!!!!!!!!!!!!!!!!!!

 

 John T   Conservative Fuddy Duddy

 

[William Briggs]

Well john I did my part by hiring that furnace tech for two hours. Thanks again for your help. Billy

[Sharon Jo]

Hi, thanks for the post on furnaces.  I have a 27 foot 1988 Ford Jamboree Ralley.  furnace NEVER works, so I just use a portable propane heater, (the small Mr. Heater little buddy heater).  heats up the whole coach in a flash.  however, along those lines, my Suburban hot water heater lights right up first time, then the next day won't light.  had a neghboring motor home resident work on it the whole day, couldn't get it to light!! then next day, fires right up! whassup!!! by the way, it starts up but clicks the whole time...HELP!!

[John "T" Nordhoff]

  Sharon, this is a bit too techy n over my head and hard to help over the net, but hey why let that stop me from trying huh

 

  Im assuming??? its an automatic electronic ignition unit based on what you say, Ive had em act that way n heres my experience: Those elec circuit board controllers ARE VERY LOW VOLTAGE SENSITIVE just cuz a test lamp shows voltage to them dont mean its high enough, if it gets much under 12 they dont work. THEREFORE insure good voltage,,,,,,,,,,see if it helps if the RV is plugged in so the voltage rises??? Ive had em act up so I removed about all the push on connectors and with a tiny brass wire brush shined em all up and used small pliers to smash them just a tad down for a tigher re fit.........The other thign that fixed one if it has a small flat ribbon cable that atatches to the circuit (ignitor) board, remove that and use a pencil eraser to shine up the little copper strips the plug goes over.

 

  If that dont fix it and theres like 12 and over volts present, then the board may be bad and you need a REAL RV tech not a shade tree amateur like myself.

 

 Usually when the T stat calls for heat theres a delay, then the elec ignitor starts her firing (tic tic tic tic) then the gas valve opens, then a sensor sees the flame and the ignitor stops firing its spark (tic tic tic tic) so if it keeps firing THATS A PROBLEM and I cant fix over the net, it may just need some slight mechanical bending/tweaking or the circuit board may be bad or the sensors bad???????

 

 I dont like the sound of that other heater youre talkin about, but its you and your RV

 

  Thats my best shot, low voltage, loose or corroded connections, then to an RV tech

 

  John T

[Mr.&Mrs.vonRabenau]

Hey Bill, I have a new furnace and mine did the same "no start". JOHN T is right on. I remember that part about the voltage.