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Old 11-09-2011, 09:08 AM   #1
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1969 27' Overlander
Albuquerque , New Mexico
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Suburban furnace problems? New NT-30...

Has anyone else had problems with newly purchased Suburban furnaces?
I just (30 days) installed a new NT-30 Suburban furnace. It seemed to work fine, until sometime last night.
I went out this morning, and it was 34 degress in there!
Turns out the furnace isn't getting ignition: It cycles, and I can see the electronic spark through the viewport, but no gas (yes, I checked the tank, and the water heater works fine, so I think I have pressure)
So, either the gas-valve isn't opening, or the control board isn't applying power to the gas valve.
I called Suburban, and all they said was to take it in for service. Nothing can be repaired by an owner. Has to be done by a service center.
Next Wednesday is my Permit Inspection, I can't have the trailer in the shop. Plus, it's full of expensive restaurant equipment. Not gonna leave it overnight with anyone!!!
Suggestions? Any known issues with Suburban?
Where can I find replacment parts, ie: control board, and gas solenoid?
Or, what's another really reliable brand of furnace. I'll replace the S.O.B. in a heartbeat, if I have to pull it out for service.
Thanks for the info.
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Old 11-09-2011, 09:36 AM   #2
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I installed a new Suburban NT-30 in my 65 Safari 2 years ago. The first winter I did have problems like yours. It would cycle but not light. I discovered that when I turned the therm. off and back on in the middle of a heating cycle it somehow messed up the board. Try to shut everything off (propane & including the power to the trailer)for 30 minutes. This can allow the board to reset. Then turn gas & AC back on. Turn thermo. up to desired setting. If it lights make sure to allow furnace to complete it's cycle before turning thermo. off. In other words wait until the blower shuts off. Mine has never missed a beat after following this procedure. If this does not do the trick then you may have to take it to a dealer.
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Old 11-09-2011, 09:54 AM   #3
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Try this

http://www.gmceast.com/technical/Nicholls_Suburban_Furnace.pdf

Perry
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Old 11-09-2011, 10:01 AM   #4
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If you have recently changed propane tanks you may have a slut of air in the line and the pilot hole is so small it will take several cycles to purge the air. Try cracking the gas line at the furnace until you smell gas and then try lighting it.
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Old 11-09-2011, 11:33 AM   #5
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Was your AS plugged into external power so the batteries were up full? Voltage is critical to the most recent Suburban furnaces. If the voltage drops below (I think 10.5 volts) at the main circuit board, the furnace will not light or operate. Sometimes the voltage at the battery is fine, but the wiring to the furnace is marginal and the voltage at the furnace, under load, is not high enough to run it. This also can be caused by a poor ground line for the furnace, so check both sides of the circuit out.

The thermostats are also suspect, especially if you have not replaced the thermostat when you put the new furnace in. Due to voltage issues (above) the wire gauge to the thermostat is also important. It should be at least #16.

Suburban has changed a lot of little things on their furnaces in the past few years so some of the older published troubleshooting information is not current.
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Old 11-09-2011, 12:02 PM   #6
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Why don't you make some voltage measurements. There are 4 wires on my old furnace. The red wire is 12V that comes on when the thermostat is above room temp. It then goes through the sail switch and the overtemp switch. If you are getting power to the board and it sparks then you need to see if there is 12V on the brown gas valve wire and the black sense wire. There will be power on these for a few seconds after turning on the thermostat. If there is no flame then it shuts the gas valve power off. If there is 12V on the gas valve and it sparks then you are not getting gas to the valve or the valve is bad. If it is really cold outside and you are using a lot of gas the pressure in the tanks can get low enough that you can't keep enough gas flowing. If you are using gas for other stuff then the pressure can get low. If you have this thing setup as a mobile kitchen you may need bigger tanks to get the flow you need. Do not pull the electrodes out unless you ground the frame of it. If yours has the spark gap and the flame sensor in the same assembly the spark will go back into the board if it is not grounded.

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Old 11-09-2011, 04:12 PM   #7
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Maybe just remove the furnace and take it in for service. Mine comes out in no more than 15 minutes. If the furnace is critical, it may be practical to install a second one for backup. All they need is gas and 12 volt and a vent hole in the skin.

Or buy a new spare and keep it on the bench in the shop. If one fails, it could be swapped out in a few minutes.
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Old 11-09-2011, 06:14 PM   #8
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I just put a new control card in mine and it works fine now. Most local RV dealers have them in stock or you can get the online and even on Ebay.

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Old 11-09-2011, 06:44 PM   #9
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I'd check the electrical connections. When we first installed our NT-30, the blower would start but no ignition and then it would just shut down. Above the gas inlet is a limit switch. After unscrewing the plate to take it apart, we found one of the electrical connectors was not connected.
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Old 11-09-2011, 08:08 PM   #10
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1969 27' Overlander
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Recommend another brand of furnace?

Good information from everyone. Thanks!
I isolated the problem down to either the control board wasn't powering the solenoid, or the gas valve wasn't operating properly. It appears to have been an electrical connection, in the end.
I checked the circuit's current flow with the meter in series with the gas valve. It was intermittant at 225mA.
Then, I forced the valve open with 12 volts on the positive terminal, during the ignition cycle. At first the valve was erratic, chattering back and forth, and of course the burner wasn't lighting or staying lit.
On a hunch, I then connected the gas valve's positive terninal back up to the board, but connected the negative terminal to a known good ground, instead of back to the circuit board ground connection.
The furnace worked the next try. So it was a bad ground.
I noticed one relay case had a glow from contact arcing, but this might have been because of a bad ground causing flyback voltage.
All of the furnace grounds are connected together with spade connections on a common terminal strip. I pulled each one, and recrimped them.
I'm not 100% sure that the board isn't suspect, but I'm certain that there was a poor ground connection as the major culprit.
Also, the propane pressure is good (other appliances work fine), but my dual cylinder regulator is defective. It continues to show green, even with both cyliinders detached. I'll be returning it for a new one.
In order to get to the circuit board and gas valve, I had to cut out a section of the side of the cabinet. Other than being cheap, there is no reason Suburban couldn't provide a sheet metal access hatch over these critical components. It shouldn't have to be up to the customer to have to modify their poor design.
p.s. Suburban was FAR from helpful. Their attitude was:"We can't take the liabilty to help you troubleshoot your furnace. You'll have to take it to a repair shop and let them deal with it." And, "We only pay a flat rate for labor. Any extra charge is your problem."
They pay 0.6 hours to replace a gas valve, and 0.5 hours to replace a circuit board. Very unrealistic, unless the furnace is sitting on a test bench. They DON'T pay for diagnostic time, either. I can't imagine why the local authorized service shop wasn't very enthusiastic about repairing a Suburban furnace.
Suburban needs a lesson in Customer Service. I think a letter to the president may help. Or maybe that's where the problem is.
Are there any better brands out there? I'm not buyng Suburban for the rest of my restaurants.
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Old 11-10-2011, 05:13 AM   #11
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I would get a spare board since they seem to be a trouble item. You probably do have a bad connection. What about warrantee?

Perry
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Old 11-10-2011, 09:53 AM   #12
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Suburban reliability & "customer service"...

One of the suppliers told me the "Dinosaur" board is a better replacement (aftermarket) for the OEM board. More robust and better built. Through-soldering instead of surface mount, etc.
I'm ordering one this morning, out of pocket.
Suburban promised they will reimburse for an on-site tech, but not the trip charge. We'll see what they "reimburse" for.
Also, they only ship UPS ground (5-7 days). I have to pay for overnight freight. No time to quibble with them. I need heat NOW. Period.
Probably won't buy another Suburban for the next trailer.
Not good customer service experience, in my opinion.
If it's unusual for their furnace to quit within 30 days, I'd think they'd be jumping all over themselves to get it fixed. If it's NOT unusual for their furnace to fail so quickly, then that means their product is poorly made and they've come to expect (accept) failure.
I expect that from a foreign made POS, but not American made!!
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Old 11-10-2011, 10:26 AM   #13
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Can't you just get a card from a local RV dealer. That is what I did to same time since I am going out of town soon.

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Old 11-10-2011, 09:16 PM   #14
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The "Dinosaur" board is 10 times the quality of the Suburban board, and costs less ($120 vs. $160). I decided it made economic sense to go that route.
I'm hardly worried whether Suburban will "honor" anything, at this point.
$500.00 lessons are cheap, in the long run.
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