RV.Net Open Roads Forum: Tech Issues: Suburban Furnace Problem

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > Suburban Furnace Problem

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 2  
Next
Sponsored By:
sandpaper600

Touring the U.S.

New Member

Joined: 07/06/2012

View Profile



Good Sam RV Club Member

Offline
Posted: 01/09/20 04:03pm Link  |  Quote  |  Print  |  Notify Moderator

So I'm doing battle again with my furnace. Suburban NT34SP. The unit has worked well for the last 16+ years, well except for that whole motor replacement thing 2 years ago.

We're in bed and I'm thinking that it's starting to get cool in the house. I check the thermostat and it says the temp is 68°. Not good, as I keep it @ 72°.

Turning the thermostat off and back on yields only a single click, then silence. No blower.

Doing some online troubleshooting tends to point me in the direction of the board, since I just replaced the motor year before last.

I checked for continuity through the sail switch and the over limit switch, both of witch were fine. So, I ordered the board.

I received my new board and installed it today. Now when the thermostat calls for heat I get a repeated relay clicking. Still no blower. I can spin the blower cage by hand, so I know it's not stuck. I also have spun it manually while trying to start it, in case it has a dead spot. No joy. If I run a hot wire to the motor it runs fine.

I have 12.6 v at the furnace. I found that if I unplug the wire from the board to the blower motor, or if I unplug the ground wire from the motor, I get just the normal one relay click.

If I manually close the sail switch, the relay stops clicking. At this point I normally would start looking at the motor again, but if it spins using a hot wire, why doesn't it work when the board feeds it voltage? (I know the board is giving it voltage at the motor because I checked.)

I'm not a furnace repair man by any means. I'm trying to dope this out with logic, but this dope has hit a wall.

Anybody had anything like this?

Lwiddis

near Jawbone Canyon, CA

Senior Member

Joined: 08/12/2016

View Profile



Good Sam RV Club Member

Offline
Posted: 01/09/20 04:23pm Link  |  Quote  |  Print  |  Notify Moderator

72 at night when sleeping in an RV? Lucky it has lasted 16 years IMO.


Winnebago 2101DS TT & 2020 Chevy Silverado 1500 LTZ Z71, 300 watts solar-parallel & MPPT, Trojan T-125s. TALL pole for flags. Prefer USFS, COE, BLM, NPS, TVA, USF&WS, state & county camps. Bicyclist! 14 year Army vet - 11B40 then 11A - (MOS 1542 & 1560)


ScottG

Bothell Wa.

Senior Member

Joined: 02/25/2005

View Profile


Offline
Posted: 01/09/20 04:36pm Link  |  Quote  |  Print  |  Notify Moderator

Not a pro by any means but since you know the motor is OK and it's getting +12V, maybe it's the negative side that's missing (ground).
Can you measure across both connections to the motor?


Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins.
2018 Silver Fox 32A.
H0NDA eu2000i

dougrainer

Carrolton, Texas

Senior Member

Joined: 06/11/2007

View Profile


Offline
Posted: 01/09/20 05:29pm Link  |  Quote  |  Print  |  Notify Moderator

Are you positive that you have the Fan motor wires connected to the correct spades on the new module board? Your model board should have the built in FAN RELAY. When you close the contac wires to start the furnace, the relay on the module board closes and outputs 12 volt positive to the Fan motor. The fan motor starts to run and the sail switch closes and starts the Ignition sequence.
1. You may have the wrong module board. Does the Malfunction happen with the original board installed?
2. You have the motor 12 volt pos wire on the wrong spade of the module board
3. You have lost the ground for the furnace, hence the clicking. Doug

sandpaper600

Touring the U.S.

New Member

Joined: 07/06/2012

View Profile



Good Sam RV Club Member

Offline
Posted: 01/09/20 11:31pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

Are you positive that you have the Fan motor wires connected to the correct spades on the new module board? Your model board should have the built in FAN RELAY. When you close the contac wires to start the furnace, the relay on the module board closes and outputs 12 volt positive to the Fan motor. The fan motor starts to run and the sail switch closes and starts the Ignition sequence.
1. You may have the wrong module board. Does the Malfunction happen with the original board installed?
2. You have the motor 12 volt pos wire on the wrong spade of the module board
3. You have lost the ground for the furnace, hence the clicking. Doug


I'm sure they are hooked up to the right terminals. I marked the power wire before old board removal. The wires and the board have different size spade connectors also. It's easy to follow the wires on this unit and see that they are correct.

The board does have the built in relay. That's what's doing the repeated clicking.

With the old board I only had one click from the relay, then nothing. I put the old board back in just as a check and it still gave just the one click.

As far as loosing ground...here's the kicker...if I unplug the ground wire for the motor, the relay clicks once. If I put a hot wire on the + side of the motor, it runs (using the existing ground.)

I have a spade connector inline from the board to the motor (from when I replaced the motor), if I unplug this and call for heat, I see 12.4 v on that wire. When I plug it back in, there is no voltage there and the relay starts clicking.

Suburban discontinued the original part number for this board and the new board is supposed to retrofit all models of furnace and water heaters. I'm wondering if my furnace, being about 18 years old, is somehow not captured in this update. The original part number is 520741 and the new board is 521099.

GenoB

Parker Strip, AZ

New Member

Joined: 01/06/2020

View Profile


Offline
Posted: 01/10/20 10:42am Link  |  Quote  |  Print  |  Notify Moderator

I just went through a bunch of trouble shooting on a water heater in my RV. I'm a very good low voltage tech and worked tech support for many years for a electronic security mfg. However my experience with RV's are limited but I do suggest the following:
1) Connect one lead of your volt meter to a good known neg or ground source and set it for DC range around 12vdc
2) Since we know the sequent of the start up for a furnace, follow that with all the wires connected
3) Turn thermostat to heat and put the other lead of your meter to the motor pos+ lead and see if voltage is present. If so then why isn't the motorr moving ? Search that. If relay clicks, then what is feeding the relay common side ? See why there is no voltage coming across the relay contacts ?
4) If the motor starts then check both sides of the sail switches to see if they are working correctly. If OK then why isn't burner starting.
5) Ck pos+ leads to gas valve and see if there is voltage there, etc
* Just follow the logic trail and see where it fails is my suggestion ...

sandpaper600

Touring the U.S.

New Member

Joined: 07/06/2012

View Profile



Good Sam RV Club Member

Offline
Posted: 01/10/20 06:21pm Link  |  Quote  |  Print  |  Notify Moderator

@GenoB--I have done this and can't figure out why it fails where it fails. I have 12.6 on the feed into the furnace. I have the same on the power terminal on the board.

When the thermostat calls for heat, I have 12.4 on the blower feed from the board ONLY if the wire to the motor is unplugged. Otherwise I get no voltage and repeated clicking of the relay.

If I unplug the motor lead from the board and power the motor direct with a hot wire, the motor runs.

If I unplug the motor from the board, everything looks normal - One click of the relay and proper voltage to the motor feed. I plug the motor back in and it starts kicking the relay in and out again.

Something is causing the relay to kick out repeatedly instead of hanging in there and passing the voltage to the motor, I just don't know what. Too large of a load for the relay rating?

I'm leaning towards wrong board at this point.

dougrainer

Carrolton, Texas

Senior Member

Joined: 06/11/2007

View Profile


Offline
Posted: 01/11/20 07:20am Link  |  Quote  |  Print  |  Notify Moderator

Have you taken a voltage reading using just the Motor Ground and positive when attempting to start? Doug

sandpaper600

Touring the U.S.

New Member

Joined: 07/06/2012

View Profile



Good Sam RV Club Member

Offline
Posted: 01/11/20 09:21am Link  |  Quote  |  Print  |  Notify Moderator

@dougrainer - Yeah, tried that. I don't get anything. The relay just clicks repeatedly and never sends any voltage.

wnjj

Cornelius, Oregon

Senior Member

Joined: 01/11/2007

View Profile


Online
Posted: 01/11/20 10:22am Link  |  Quote  |  Print  |  Notify Moderator

sandpaper600 wrote:

Something is causing the relay to kick out repeatedly instead of hanging in there and passing the voltage to the motor, I just don't know what. Too large of a load for the relay rating?

I'm leaning towards wrong board at this point.


If you find that’s the case, you could always get a 12V automotive relay. Power the relay coil with the board’s fan output and use a direct fused 12V source to switch to the fan. You could even try that temporarily just to see if it operates if it seems to kludgy for a permanent fix.

It’s unlikely but possible your replacement fan motor is failing or drawing too much power. Try running the motor with an ammeter in series to see how much it’s taking.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 2  
Next

Open Roads Forum  >  Tech Issues

 > Suburban Furnace Problem
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2020 CWI, Inc. © 2020 Good Sam Enterprises, LLC. All Rights Reserved.