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Old 11-07-2021, 05:09 PM   #1
Winnebago Victim
 
Join Date: Dec 2018
Location: Sandy, Utah
Posts: 15
Suburban Furnace SHD-2542Q Dual-Stage

Hello all,

2015/2016 Adventurer W37F furnace fails to function in Stage 1.
As near as I can tell, it attempts to start as the blower runs but ignition never happens. This cycle happens several times and then the furnace goes into shutdown/lockdown. I have to use the thermostat to turn off the heating function to restart/reset the furnace. After reset, if the temp difference between the thermostat setting and the actual room temp is small, which then sets up a Stage 1 heating cycle, the system goes through the same multiple failed attempts to heat resulting in another lockdown.

However, after restarting the furnace from completely off and setting the thermostat high enough to call for Stage 2 (about 5-6 degrees) the furnace starts up perfectly & heats the coach.

Great? No, because I go back to bed and when the furnace goes through a normal cycle to start again, it calls for Stage 1 and fails again.

Does anyone have experience is resolving this situation? I pulled everything apart and all looks great & clean. It appears that 2-Stage furnaces are not common. I really like this 2-Stage unit as it normally only needs to run in Stage-1 as I don't winter camp, just for chilly nights, so it runs very quietly.

There are still some parts and circuit boards available. I don't think it would be the thermostat as it calls for heating when needed. It is a RVComfort.zc controller setup for 2-Zones.
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Old 11-07-2021, 06:09 PM   #2
Winnebago Master
 
Join Date: Nov 2018
Location: Pflugerville/Austin, Tx
Posts: 7,371
Furnaces on RV often operate somewhat the same bu tthere are also often small differences which really throw us off if we are not careful, so this is a time when I want good firm info and look online for the best manuals I can find.

In this case, you appear to have given exactly the right info to head directly to the right manual and the right part! Good show on getting the info!

This appears to be the correct manual:
https://manuals.heartlandowners.org/...11-05-2015.pdf

And looking down through it looks like I would start on page 28 to carefully follow what is expected to happen and that will give you a firm idea of where to look for the solution.

Can we be sure the battery voltage is not a problem when starting on the single stage as that is one first point for shutting down if it drops below 9 something?

Just as top-o-the-head, it doesn't sound like the most frequent things I think of like insects on the sail switch , etc. as the second stage lights off okay, but then that is the time to go with the folks who build the thing!

Good luck and let us know how it turns out or if there may be other points??
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Old 11-07-2021, 09:21 PM   #3
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Join Date: Dec 2018
Location: Sandy, Utah
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Nice manual

Hello Morich,

Thanx for the 2015 manual. I found a 2007 version but it was lacking so I came here. Unfortunately the 2015 version is still lacking. Neither has a schematic for the 2542 model and both state that the motor and gas valve are 2-Stage devices. Unless someone here has more insight I'll probably need to call Suburban for help and hopefully a schematic. That would make life simple.

Len
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Old 11-20-2021, 09:35 AM   #4
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Join Date: Mar 2010
Location: Anchorage, Alaska
Posts: 18
Our Suburban SHD-2542 two stage furnace started operating erratically after being in storage for 19 months due to COVID. Initially it would start and heat but shut down before reaching the set point. Then it would not restart without cycling the thermostat off and back on. Then it would operate a shorter length of time. Then it would not restart even after cycling the the thermostat. Waiting a day, it would start once but not reach the set point before shutting down. Thought that maybe it was a failing limit switch. Pulled the furnace, checked the limit switch. It was fine. Checked the board. Output voltage with the motor lead connected was 3 to 4 volts when the thermostat clicked on and then went to zero. According to a Suburban troubleshooting manual that was an indication of a bad board. Researched Suburban literature and determined the Suburban part no. was 232806. The number on the board was Fenwal 06-235773-007. Could not find any source that listed the Fenwal number. Did find a couple sources that indicated that the Suburban 232806 board was on backorder. Note that there is confusion on the boards because the Suburban SHD-2542 (supposedly no longer manufactured) has two boards, one on the side of the motor and one on the end of the motor. The one on the end is supposedly Suburban 232806. The one on the side is supposedly Suburban 93267. An RV technician indicated that Dinosaur board Fan 50 Plus PINS is an exact replacement for the original OEM board. Dimension wise, plug wise and terminal wise it is the same. Removed the Fenwal 06-235773-007 board and installed the Dinosaur Fan 50 Plus Pins board and the furnace seems to run fine although not certain how to tell which state it is operating on. Also note that only after installing the Dinosaur board as it came out of the box was it discovered an instruction sheet indicating that certain terminal on the Dinosaur board can be jumped differently. I made not changes. Also the Dinosaur board is fused and has a Red and Green LED which indicate power and flame for ease of troubleshooting. Good Luck.
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Old 11-20-2021, 09:43 AM   #5
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Join Date: Mar 2010
Location: Anchorage, Alaska
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PS: Calling Suburban was of little help. They do not recommend any non-technician work on the furnace and will only give you the names and phone numbers for technicians around the US. They would not tell me anything on the availability of the OEM board but suggested that I call Camping World.
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Old 11-22-2021, 05:51 PM   #6
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Join Date: Dec 2018
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Troubleshooting

Thanx Market, the more help the better. Hopefully this info will help someone else someday.

I did call Suburban and got the same result as you. Quite unfriendly to self us repair folks. Fortunately, with my background, I am as capable as someone Suburban would offer. I just don't have the correct manual but that won't stop me.

I used what info I could find, dug into the furnace and made my own block diagram/schematic. What I determined is that the board right in front by the blower is the Stage-2 controller, part #232806. The board at the left end of the blower they call the Module board, part #521099. It also makes the HV spark and starts Stage-1.

The 4-wire connector also on the left side is for the thermostat:
Yel-Gnd; Orn-Stage-2 call (W2) to the Dual-Stage board; Red-12VDC power; Blu-Stage-1 call (W1) to the Module/HV board after going thru the Limit, Sail & chassis on/off switch. This switch is REAL handy during testing. Turn it off, go set the thermostat as desired for Stage-1 or 2, come back and flip the switch on to start the testing/heating.

All the Yel wires are ground.

Both boards each have a Brn wire to activate their own gas valve (p/o Dual-Stage). Both boards also each have a Red wire to run their own blower motors (again p/o Dual-Stage).

The 12VDC to operate the Dual-Stage board goes thru the large relay on the Module board using the two 1/4" spade connectors next to the relay rather than the 6-position edge conn that only has 4 wires. This means the Stage-2 board can't operate w/o the Module board triggering first, so Stage-1 has to have already been called.

I did this tracing after I got back from our trip with the problem. After doing this research I was going to find the problem, I'm READY!

Of course, the furnace worked perfectly, NTF. So what changed? Only two things I can think of.
1. Altitude; the failure happened at 10,400'. My test session was at home at 4200'.
2. Voltage; we were in a Federal CG w/no hookups. We ran the gen before bed and the residential fridge ran fine all night, plus the furnace could be forced into running ok, so I don't think that was it.

The Stage-1 gas valve now comes into focus as everything else checks out to a degree. I can't find a replacement for it although I did find both boards are available. I also saw the Dinosaur board you mentioned.

I guess I'm stuck until the next trip (Spring 2022) to do more testing. At least I have the info now to troubleshoot on the spot.

BTW, the Module board edge conn is pinned:
1- Red, switched 12VDC out to main blower.
2- Blu, switched 12VDC from thermostat thru all 3 switches I mentioned.
3- n/c
4- Brn, out to Stage-1 gas valve.
5- n/c
6- Yel, gnd
Without a real schematic, I don't know if the Module board is powered from the Pin-2 thermostat voltage or the 1/4" spade terminal power source by the relay. Maybe both to a degree, but I suspect the 1/4" spade is more correct.
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Old 09-16-2022, 04:13 PM   #7
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Join Date: Dec 2018
Location: Sandy, Utah
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Problem solved!
It was the sail switch. It's reasonably accessible, inside the blower housing.

It is mounted upside-down with the sail on the bottom. Comparing the replacement to the original, the new switch has a longer sail by 1/4" & required slightly less pressure to operate. My issue was the failure at elevations of 10k feet where the air is thinner makes sense now.

With the furnace disassembled further than before I discovered that I have some errors in my wiring info previously offered. Please ignore as the Blue wire does come from the thermostat but it does NOT go thru the Limit & Sail switches. Sorry!
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