Suburban furnace problem - Problem Solved

6

6.7LMegaCab

Well-known member
Hi all! Day one out hunting with my son. Last night I fired up the furnace and before I went to bed, I lowered the thermostat to about 67 degrees. After I lowered it, it never came back on and so we woke up to a cold trailer.

When I turn the thermostat on, I hear a click in the AC and while out at the furnace, I also hear a click. I don't see any lights, so I don't know if this model has a troubleshooting indicator on it or not.

I pulled the exterior cover off and there is nothing jamming up the blower motor.

Batteries are charging fine and are not low.

I read through 2 troubleshooting guides and neither really seemed to address the problem or how to troubleshoot it.

Is the furnace tied to one of the circuit breakers in the battery compartment? None of the fuses on the fuse panel are lit up, yet none are marked for a heater or I can't read the chicken scratch writing.

Any help to get us going in the right direction will be greatly appreciated.

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JohnDar

JohnDar

Prolifically Gabby Member
There isn’t much electrically to a Suburban furnace. If it sounds like it’s trying to light and won’t, it’s a good chance the circuit board needs replacing. Check inside the burner tube to be sure no insects have found a new home, too.


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danemayer

danemayer

Well-known member
The click in the A/C is a relay that connects 12V DC from the fuse box to the furnace. After the click, the next thing that's supposed to happen is the furnace blower runs for about 25 seconds. Then, there should be an ignition attempt.

If the blower doesn't run, the furnace may not be getting 12V. Checking for a blown fuse by looking at the LEDs can be misleading because the LED will illuminate ONLY if the fuse is blown or removed, AND there's a load on the circuit. Check again right after you hear the click at the A/C. If no lights, check each fuse visually. If all the fuses look ok, and you have a meter, one by one, remove and check the continuity of each fuse.

Also, on the tank level monitor, there's an indicator of battery level. With a fully charged battery, you should get 4 lights. Your battery might be fully charged, but there's a 12V mini-circuit breaker near the battery that has a manual reset. If it trips, you won't get power to the fuse box. If you're not on shore power, that's probably not your problem or the thermostat would be dark.
 
6

6.7LMegaCab

Well-known member
danemayer said:
The click in the A/C is a relay that connects 12V DC from the fuse box to the furnace. After the click, the next thing that's supposed to happen is the furnace blower runs for about 25 seconds. Then, there should be an ignition attempt.

If the blower doesn't run, the furnace may not be getting 12V. Checking for a blown fuse by looking at the LEDs can be misleading because the LED will illuminate ONLY if the fuse is blown or removed, AND there's a load on the circuit. Check again right after you hear the click at the A/C. If no lights, check each fuse visually. If all the fuses look ok, and you have a meter, one by one, remove and check the continuity of each fuse.

Also, on the tank level monitor, there's an indicator of battery level. With a fully charged battery, you should get 4 lights. Your battery might be fully charged, but there's a 12V mini-circuit breaker near the battery that has a manual reset. If it trips, you won't get power to the fuse box. If you're not on shore power, that's probably not your problem or the thermostat would be dark.
Click to expand...
Thank you! I found the fuse. Pulled it, turned the furnace on via the thermostat and got the red light. Turned it off and put the fuse back in.

I checked the battery indicator when we got back to see how low they were after being out since 0600. The 4th (full LED) was barely flickering. Which makes sense considering the fridge was the only one pulling the tiny bit of power.

I'm guessing it's the board if there is a click at the furnace and click at AC that it runs through, but no blower. I guess we will be bundling up for the night.

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6

6.7LMegaCab

Well-known member
wdk450 said:
Here's a link to a You Tube Video on troubleshooting a Suburban RV furnace with the exact same problem you have. The problem was bad blower motor relay contacts on the circuit board:

I think this is a common problem.

More similar videos here: https://www.youtube.com/results?search_query=suburban+rv+furnace+troubleshooting

You can get replacement circuit boards on E-Bay, Amazon, RVColingunitwarehouse.com, or directly from Dinosaur Electronics.
Click to expand...

Wow! Thank you for this! I'm betting it's the control board after watching that video. Gotta figure out who I can get one from soon or at least delivered by Wednesday to my parents as once my son tags out, we're heading to their place for Thanksgiving...need to have heat when the rest of my family joins us.

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09Busaman

09Busaman

Active Member
I couldnt tell from your description but does it blow air for 3 seconds or so then shut off, or just wont come on at all? Ours gave us fits because a a sail switch being dirty.
 
wdk450

wdk450

Well-known member
The dirty little secret about RV furnaces is that they use up your batteries VERY QUICKLY if boondocking (not connected to grid power). Get yourself plugged in (then you can use electric heaters), or get a generator going during the day to recharge your batteries if you can't get plugged in.

I stay in RV parks and keep plugged in. I use electric heat. I have used my furnace about 1 time in 2 years. Of course, I stay in Southern California where overnight freezing is rare.
 
6

6.7LMegaCab

Well-known member
Stove works fine. Fridge on propane works fine. Batteries are fine. Fan on heater will not turn on. I hear a click at the AC and at the heater when I turn the thermostat to heat. Nothing happens. Fuse is good.

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2019_V22

2019_V22

Well-known member
The next step would be get to the blower and understand if it is obstruction free, (able to be turned by hand), and if the motor it's self is getting power from the board, or controlling relays.
 
6

6.7LMegaCab

Well-known member
Motor spins freely. I know power is getting to the circuit board because there is an audible click once power is signaled (ie calling for heat at the thermostat).

We are home now and just decided to forgo the repair while away for a few reasons.

1. Mobile repair guy was the only one that had a new board on hand, but he wanted $25 for a service call, $125 to troubleshoot, and wouldn't give me a price for the board.

2. The local RV parts place wanted to sell me a Dinosaur Electronics board for $170. One of the online dinosaur retailers has it for $96.

That tells me dinosaur electronics doesn't really care what their boards are sold for, regardless of the 3 Year Warranty, which is the added value that the local RV shop tried to sell me on.

I'm going to pull the board tonight or tomorrow and get out the multimeter. I'm willing to bet I can fix it myself and while it's out, I'm going to design that board in NI MultiSim/UltiSim and perhaps see what I can get new boards printed for if this board is bad. About 6 years ago I designed a pinewood derby track timer circuit board for about $30 total. These boards are about the same size.

I know people need to make a living but there is a saying that you can never hire someone to do something for less than what you can do yourself.

Now, I'm all ears if there is something behind the furnace cabinet that also calls for air to get the motor to spin. The schematic doesn't indicate something like that...or I missed it.

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2019_V22

2019_V22

Well-known member
It sounds like either the board relay contacts are shot, or the motor brushes are worn. Before board removal check the motor connectors to see if they are getting 12v from the board relay, and or just apply 12v to the motor terminals.
DigiKey, and Mouser are all go-to's for replacement board components if you are good at soldering the parts on the existing board. All components, IE: relays have identifiers printed on them for replacement purposes.
 
6

6.7LMegaCab

Well-known member
2019_V22 said:
It sounds like either the board relay contacts are shot, or the motor brushes are worn. Before board removal check the motor connectors to see if they are getting 12v from the board relay, and or just apply 12v to the motor terminals.
DigiKey, and Mouser are all go-to's for replacement board components if you are good at soldering the parts on the existing board. All components, IE: relays have identifiers printed on them for replacement purposes.
Click to expand...

Good call on that! I will check for 12V at the relay and apply 12V to the motor just to be sure the motor isn't bad. It's odd that something that was just fine one day suddenly stops working the next.

Both Digikey and Mouser are definitely my go to electronic parts suppliers. One of them I have some parts saved to try to revive an old car audio amplifier for my brother. All the large caps are bulging on it. He said of all the amps he's used, this one was the cleanest sounding.

I'll check it out tomorrow and report back the findings.

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wdk450

wdk450

Well-known member
The motors are on E-Bay, but there are several part numbers, and they seem pricey.
www.ebay.com

Suburban Rv Furnace Blower Motor for sale | eBay

Get the best deals for Suburban Rv Furnace Blower Motor at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!
www.ebay.com

I found a You Tube Video on changing the Suburban RV Furnace blower motor brushes. They guy found them for cheap at Ace Hardware, but his video was kind of flakey saying "cut this, remove that, etc." without showing you what this and that were.
 
6

6.7LMegaCab

Well-known member
Thanks all! So I've been out here troubleshooting this thing this morning.

I checked for voltage at the red spade connectors on the control board which should provide the +12V to power the blower and provide the necessary voltage for everything else. There isn't any power getting to the board. I pulled and checked that every fuse at the main panel is good and they are.

I connected a battery directly to the blower and the blower powered on with no hesitation.

I also pulled the dust cover on the main AC that the t-stat for the furnace runs through and all the wires that say +12V tests good on the multimeter.

Is there some other hidden fuse or CB somewhere that is between the combo 120 main breaker/ 12V fuse panel that controls power to the furnace? There is a fuse for the furnace on that main panel and when heat is called for and pull the fuse, the LED lights up, so I know that is good.

What else is there that I can check?

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