Removing Suburban Furnace SF42 from Itasca Horizon

[jhanan]

Hi all, I have an Suburban SF42 Furnace in the Horizon with only outside access to the unit. Anyone have the steps to remove this unit? Mine is screwed and glued in and looks a bit difficult to remove it.

I need to remove the unit as it will not fire. The fan runs for 4 minutes and then shuts off. No clicking sound. Does not sound like sail switch is the issue because the fan runs for 4 minutes which is a long time. Might be the ignitor or something else. I see no access to the ignitor from the outside, but I still don't have the cover peeled off yet. I have good power and full propane and all the other applicinces working fine such as the fridge and water heater.

Any advice or videos out there for a Class A Winnebago?

Thanks, Jeff

[Old-Biscuit]

Installation/Operation Manual ALL Models
Pg 7
SF removal
Pg 10
SF Exploded view with outside access
http://techsupport.pdxrvwholesale.co...ing-Manual.pdf




That model uses a 'blower circuit' on the circuit board to start/stop Fan.
Fan has to CLOSE sail switch for DC to flow thru High Limit Switch and go to Circuit Board in order for Circuit Board to send DC to Gas Valve/Spark Electode
BO DC back to circuit board via Sail Switch/Limit Switch circuit no attempts at ignition.

[jhanan]

Originally Posted by Old-Biscuit

Installation/Operation Manual ALL Models
Pg 7
SF removal
Pg 10
SF Exploded view with outside access
http://techsupport.pdxrvwholesale.co...ing-Manual.pdf




That model uses a 'blower circuit' on the circuit board to start/stop Fan.
Fan has to CLOSE sail switch for DC to flow thru High Limit Switch and go to Circuit Board in order for Circuit Board to send DC to Gas Valve/Spark Electode
BO DC back to circuit board via Sail Switch/Limit Switch circuit no attempts at ignition.

Thank you Old Biscuit! So maybe is a stuck sail switch then after all. I will get in there and figure it out soon as have trip on Nov 9!

[jhanan]

Nice troubleshooting guide here so based on my 4 min run time the controller is trying all 3 start tries and that mean the sail switch is ok otherwise the fan would stop after 30 seconds so it's down to either the electrode module or the gas valve. The document seems clear will just take more time trouble shooting and see if mice got inside the furnace wiring

[jhanan]

Peeled off the cover and discover no mice and fans and motor all look good and I sail switch is fine as expected and I can hear it trying to start and can small a wif of propane so valve is opening and so decided to cycle it a few more time and well it finally fired but the burn seems and sounds intermittent like it will burn hot for a few seconds and then stop and restart. It ran down for about 20 min before ai shut it down to troubleshoot more tomorrow

[Old-Biscuit]

Need to pull that intake/exhaust ports back off.....remove burner assembly and CLEAN it


Also blow compressed air thru heat exchanger while you have burner assembly removed and make sure no critters have set up house (nests etc)


Intermittant firing can be from heat exchanger getting too hot (High temp limit switch opening)....obstructed exchanger
OR can be due to heat NOT being removed....blocked registers/collapsed ductwork

OR can be due to lack of return air (stuff being stored around furnace cabinet)

[jhanan]

Thanks old biscuit I will pull the unit out and see whats going on

[Tuquala]

Pull out unit and check the position of the igniter. Acts just like ours did last year. The igniter was slightly mispositioned, not "firing" onto a gas hole in the tube, and was closer than recommended. Tech widened the gap, like a car spark plug, which makes the spark "hotter" due to the larger gap. Has worked perfectly since then!! Also, check the LP pressure if you can obtain a manometer. Ours was very slightly low, and got adjusted up to just over max. That may have helped just as much, but do know that that the igniter gap adjustment made the furnace start quicker, first try almost everytime.

You will need a gasket for the LP connection to the burn tube for disassembly, and a "modified" wrench or crows foot type to get the LP pipe off of burner hsg to check the igniter.

[Tuquala]

Just noticed your post aboot getting furnace to run, and then "hot" cycling. Ours does that regularly when on, heats nicely, burner shuts off, fan stays on, then burner ignites again. Does this until the thermostat setting is reached. Tech says that mfgs now days don't put enough flow area into RVs. He told me not to worry about it, or to change the hitemp cutoff switch to a higher rating. Said it really doesn't cause any damage or problems, since the switch is working like it should.

I plan (best laid!!) to open up the front outlet in the bedroom to a larger vent and maybe put an outlet under the bed to give a bit more flow to the system. One of these days!!

[Old-Biscuit]

Originally Posted by Tuquala

Just noticed your post aboot getting furnace to run, and then "hot" cycling. Ours does that regularly when on, heats nicely, burner shuts off, fan stays on, then burner ignites again. Does this until the thermostat setting is reached. Tech says that mfgs now days don't put enough flow area into RVs. He told me not to worry about it, or to change the hitemp cutoff switch to a higher rating. Said it really doesn't cause any damage or problems, since the switch is working like it should.

I plan (best laid!!) to open up the front outlet in the bedroom to a larger vent and maybe put an outlet under the bed to give a bit more flow to the system. One of these days!!

RV Tech is an idiot.


Furnace Mfgs have High Temp Limit Switch installed as a SAFETY device and it's temp setting is based on fan cfm/burner btu and expected discharge/return air requirements

RV Mfgs might ignore the discharge/return air requirements but even they aren't THAT STUPID.....open up a big can of liability issues.

IF furnace is 'limiting'-----operating on High Temp Limit Switch changing it out for a Higher Temp Setting is asking for MAJOR problems ie: FIRE, CO Exposure etc

High Temp Limit Switch shuts down ALL DC to circuit board so gas valve closes.
No more Flame or raw fuel flow

Fan continues to run cause Thermostat set point has not been satisfied therefore DC is still going to fan motor circuit, heat echanger cools down, high temp limit switch closes......firing resumes.

Excessive heat can cause heat exchanger to CRACK which will allow CO into room side of airflow...CO Posioning BAD!
A Higher Limit set point would allow flame to operate outside of furnace specs which could result in a FIRE

That RV Tech is an idiot!

High Temp Limit Switch is OPENING
*Because Exhaust is obstructed (combustion heat can't be removed)
*Because Return air is obstructed (Room return air is not sufficient to cool exhanger)
*Because Discharge air is obstructed (lack of airflow THRU heat exchanger---too many registers closed/blocked or ductwork collapsed)
*Because LP System pressure is TOO High (Overfiring)
*Because High Temp Limit Switch is faulty (rare)


The more 'uncontrolled events' (High Temp Limit Switch operating is an uncontrolled event vs thermstat set point) the more likelyhood of damage due to excessive thermal stressing of heat exchanger
(heat/cool/heat/cool/heat/cool cycles in a short time frame VS Heat/cool then long delay before next cycle)


YOU can goggle the Service Manual for YOUR specific Brand/Model and read about the REQUIREMENTS for disharge/return air flows
YOU need to FInd/Fix the cause of your furnace 'LIMITING' cause it is NOT going to get better and could become dangerous...family!

[oldbeek]

Originally Posted by Old-Biscuit

RV Tech is an idiot.


Furnace Mfgs have High Temp Limit Switch installed as a SAFETY device and it's temp setting is based on fan cfm/burner btu and expected discharge/return air requirements

RV Mfgs might ignore the discharge/return air requirements but even they aren't THAT STUPID.....open up a big can of liability issues.

IF furnace is 'limiting'-----operating on High Temp Limit Switch changing it out for a Higher Temp Setting is asking for MAJOR problems ie: FIRE, CO Exposure etc

High Temp Limit Switch shuts down ALL DC to circuit board so gas valve closes.
No more Flame or raw fuel flow

Fan continues to run cause Thermostat set point has not been satisfied therefore DC is still going to fan motor circuit, heat echanger cools down, high temp limit switch closes......firing resumes.

Excessive heat can cause heat exchanger to CRACK which will allow CO into room side of airflow...CO Posioning BAD!
A Higher Limit set point would allow flame to operate outside of furnace specs which could result in a FIRE

That RV Tech is an idiot!

High Temp Limit Switch is OPENING
*Because Exhaust is obstructed (combustion heat can't be removed)
*Because Return air is obstructed (Room return air is not sufficient to cool exhanger)
*Because Discharge air is obstructed (lack of airflow THRU heat exchanger---too many registers closed/blocked or ductwork collapsed)
*Because LP System pressure is TOO High (Overfiring)
*Because High Temp Limit Switch is faulty (rare)


The more 'uncontrolled events' (High Temp Limit Switch operating is an uncontrolled event vs thermstat set point) the more likelyhood of damage due to excessive thermal stressing of heat exchanger
(heat/cool/heat/cool/heat/cool cycles in a short time frame VS Heat/cool then long delay before next cycle)


YOU can goggle the Service Manual for YOUR specific Brand/Model and read about the REQUIREMENTS for disharge/return air flows
YOU need to FInd/Fix the cause of your furnace 'LIMITING' cause it is NOT going to get better and could become dangerous...family!

Further note ,, the high temp switch is 410 degree in the fire box. DON"T mess with that. I had this problem with the heater on a test bench. No ducts attached at all. Finally installed a jet 2 sizes smaller. The board will let the heat box cycle on and off 6 times then time out for 1 hr. This happens to me when I am trying to bring temp in trailer up to temp from 15 degree. The way to bypass this problem safely is to put a switch in series to the 12 volt fuse controlling the heater. Flip power off for 5 seconds then turn it back on. Heater board will run you through another 6 cycles. Turning off and on the thermostat does nothing for this problem. The board is a computer. What do we do??? Remove the power and reconnect.

[Roy1]

Old biscuit is telling it to you straight the tech is an idiot. Most high limit switches are set at 1** degrees auto reset with a manual reset high limit 10 or 20 degrees higher find and fix the obstruction even if it means another duct or larger outlet or larger return opening don’t mess with higher temp limit switches your life may depend on it.

[oldbeek]

Originally Posted by Old-Biscuit

Installation/Operation Manual ALL Models
Pg 7
SF removal
Pg 10
SF Exploded view with outside access
http://techsupport.pdxrvwholesale.co...ing-Manual.pdf




That model uses a 'blower circuit' on the circuit board to start/stop Fan.
Fan has to CLOSE sail switch for DC to flow thru High Limit Switch and go to Circuit Board in order for Circuit Board to send DC to Gas Valve/Spark Electode
BO DC back to circuit board via Sail Switch/Limit Switch circuit no attempts at ignition.

. The sad truth is that the manual does not include the repeat cycling feature that happens when the high limit switch in the fire box opens. The board will try to relight 6 times then time out for 1 hour. The first step in trouble shooting is to disconnect all power, then reconnect power. Pull and replace heater fuse.

[Old-Biscuit]

Originally Posted by oldbeek

Further note ,, the high temp switch is 410 degree in the fire box. DON"T mess with that. I had this problem with the heater on a test bench. No ducts attached at all. Finally installed a jet 2 sizes smaller. The board will let the heat box cycle on and off 6 times then time out for 1 hr. This happens to me when I am trying to bring temp in trailer up to temp from 15 degree. The way to bypass this problem safely is to put a switch in series to the 12 volt fuse controlling the heater. Flip power off for 5 seconds then turn it back on. Heater board will run you through another 6 cycles. Turning off and on the thermostat does nothing for this problem. The board is a computer. What do we do??? Remove the power and reconnect.

410*F...???
TYPO
Did you mean 140*F?


High Temp Limit Switches range from 130*F to a High of 190*F
They are sized based on orifice/burner and air flow specs





Installed an orifice 2 sizes smaller......???
Your LP Supply Pressure was TOO HIGH causing the Overfiring.

Originally Posted by oldbeek

. The sad truth is that the manual does not include the repeat cycling feature that happens when the high limit switch in the fire box opens. The board will try to relight 6 times then time out for 1 hour. The first step in trouble shooting is to disconnect all power, then reconnect power. Pull and replace heater fuse.

What Brand/Model is YOURS??