Suburban furnace won't heat when connected to shore power

[RClifton]

Hi all,

My wife and I purchased a new to us 2016 Heartland Bighorn 3750FL on Friday and overall we are loving it, with a few minor exceptions. One of them is the Suburban furnace. I'm unclear on the exact model # at the moment as it's buried in the basement behind some panels and above the water heater.

When I am connected to shore power and set the thermostat to Furn the unit will come on and run for just a little over 4 minutes. It never produces heat, and the outside exhaust never gets hot. There is a small odor of propane when it first fires up but that's it, after the 4+ minute run it shuts off and the unit remains locked out until I power the thermostat on and off.

If I disconnect shore power and the battery momentarily and then reconnect the battery the unit will immediately fire up and heat as it should. It will cycle on and off as the temperature changes just as you would expect.

However, if I reconnect shore power after the unit is running it will continue to run and heat but once it reaches the set temperature and turns off when heat is called again it will go through the original issue and turn on but not heat. The only way to get it to heat again is to disconnect shore power and momentarily disconnect the battery.

Does anyone have any ideas? I am leaning towards a possible converter issue as I can't really figure out what else it could be.. Thanks!

[Skip426]

Measuring supply voltage at the furnace when the issue is happening could provide a clue , I haven't heard of a shut down due to over current supply , but I guess it's possible . I have had a low voltage warning; from my thermostat; when a converter failure dropped voltage to 10.6 volt from the coach batteries.

Furnace manual would provide details.

EDIT : Converter output voltage could be measured at the converter or batteries.

[Old-Biscuit]

Fan comes on but no heat from exhaust so Gas is NOT igniting/proving it lit so it shuts down/locks out

Furnace is 12VDC ....has nothing to do with 120VAC

Battery supplies the DC Voltage or the Converter does when AC power is available

Not lighting off
*Could be Low DC Voltage
*Could be inadequate airflow...low voltage/bad combustion wheel
*Could be Sail Switch..low airflow/stuck-hung up paddle/dirty
*Could be lack of spark...bad gap/bad electrode
*Could be bad burner...rusted out
*Could be bad gas valve solenoid
*Could be bad circuit board
*Could be......

Not cycle as per t-stat set point....lock out
*Could be t-stat
*Could be circuit board

Unfortunately Suburban does not have exterior access panel so components can be tested W/O removing and bench testing the furnace

Sequence of Operation starts on pg 26
Troubleshooting Guide starts on page 30
http://techsupport.pdxrvwholesale.co...ing-Manual.pdf

[RClifton]

Originally Posted by Old-Biscuit

Fan comes on but no heat from exhaust so Gas is NOT igniting/proving it lit so it shuts down/locks out

Furnace is 12VDC ....has nothing to do with 120VAC

Battery supplies the DC Voltage or the Converter does when AC power is available

Not lighting off
*Could be Low DC Voltage
*Could be inadequate airflow...low voltage/bad combustion wheel
*Could be Sail Switch..low airflow/stuck-hung up paddle/dirty
*Could be lack of spark...bad gap/bad electrode
*Could be bad burner...rusted out
*Could be bad gas valve solenoid
*Could be bad circuit board
*Could be......

Not cycle as per t-stat set point....lock out
*Could be t-stat
*Could be circuit board

Unfortunately Suburban does not have exterior access panel so components can be tested W/O removing and bench testing the furnace

Sequence of Operation starts on pg 26
Troubleshooting Guide starts on page 30
http://techsupport.pdxrvwholesale.co...ing-Manual.pdf

Thanks, I had already looked through their manual but I don't believe the heater is the real issue. It works perfectly when on battery, it is only when it is plugged into shore power that the issue arises. I'm going to crawl in behind the panels in the basement tomorrow and start measuring the converter output, checking grounds etc..

The only thing that doesn't make sense is that in order to get the furnace to work properly after I remove shore power I must disconnect the battery momentarily before reconnecting it. After that it works perfectly on battery for as long as I tested it (roughly 6 hours).

[Persistent]

Old-Biscuit knows what he is talking about. Get more specific advice by providing make and model of furnace.

The igniter in the furnace requires a proper furnace to frame and frame to battery negative ground. It is possible that the grounding changes when you connect to shore power.

Loose or corroded grounding is common in RV's. Old-Biscuit know better than I, how this works. Try connecting a jumper from the furnace sheet metal to a frame ground point and or to the battery negative.

RV power systems are wired many different ways. Owners change the wiring at will. There is no telling how yours works without tracing wires. Sometimes transfer switches will ground the 120 volt AC neutral (bonding) for inverter or generator use.

If ground wires are not working correctly, the igniter may not spark, or the fan may not spin up fast enough, or the gas valve may not open properly.

Ultimately, you may need to get to the furnace to troubleshoot. However, you may be able to hear the igniter.

Can you hear the igniter spark when it tries to light. It should make a "clicking" sound. This should happen three times before a failure to ignite logic shuts the furnace down.