RV furnace motors are scapegoats. They are often blamed for problems not at all their fault. Many a motor has been replaced by a well-meaning DIYer only to discover that a sail switch, circuit board, or cracked fuse was the true culprit. And since the average RV furnace motor costs around $150, that’s a painful mistake to make.

How can you tell if an RV furnace motor has failed? Is it easy to replace a furnace motor? I’ve replaced a handful myself, and while the job isn’t technically difficult, it’s rather like changing the spark plugs on a Subaru flat-six engine: The access is the challenging part!

But first, let’s learn a little more about your RV furnace, how to replace an RV furnace motor, and why your furnace ain’t blowing like it used to. 

Introduction to the RV Furnace Motor

The motor is the whirring heart of your furnace. Most RV furnaces have a single dual-shaft motor that spins two fan wheels at the same rpm.

• One fan is a blower wheel that recirculates interior air through a ductwork system over a heat exchanger. It moves the hot air that you feel coming out of the floor vents.
• The other fan is a combustion wheel that brings in air from the outside for the propane combustion and then sends out the gases. It moves the hot air you feel if you stick your hand next to the exhaust pipe (although don’t do that).

It is a common misconception that furnaces exchange air with the outdoors. That just isn’t true. No air is transferred between inside and outside; only heat is transferred through a set of serpentine tubes in the heat exchanger. No toxic combustion gases or fumes should be getting inside your camper. 

>>> READ MORE: The Difference Between Gas Heat & Electric Heat in an RV

As motors go, RV furnace motors are rather primitive. They are single-speed only. Most are series-wound: one positive wire, one negative wire. The vast majority of RV furnaces run on 12-volt DC electricity only; a small selection of park model furnaces run on 120-volt AC electricity. These park model furnace motors may use AC asynchronous motors and a capacitor. But for everything else, it’s a simple 2-wire connection and nothing else. 

Unlike more complicated motors, RV furnace motors are rarely rebuilt. They are not designed with easily replaceable bearings or windings. If you try to rebuild an RV furnace motor, you’re on your own!

Symptoms of a Failing RV Furnace Motor

If an RV furnace motor is going bad, what are some of the symptoms?

Low Heat Output

You may feel less heat coming out of the air registers. You may notice that the furnace is unable to maintain a temperature setpoint once the ambient temperature dips to below freezing. 

Fair warning: This is difficult to diagnose as a DIYer. Lower airflow than usual can also be caused by the following:

• Insect nests
• Rodent nests
• Damaged electrode
• Burnt-out burner head
• Damaged or blocked ducts 
• Faulty gas solenoids
• Broken fan wheel

Low Airflow

You may feel less air moving out of the air registers. You also may notice less air coming out of the exterior exhaust pipe.

Fair warning: This is difficult to diagnose as a DIYer. Lower airflow than usual can also be caused by the following:

• Insect nests
• Rodent nests
• Damaged ducts 
• Broken fan wheel
• Low incoming voltage (wiring, fuse, converter, etc.)

Furnace Shuts Off After 30 Seconds

If your furnace kicks on, whirrs for about 30 seconds, and then turns off, it is most likely the circuit board has determined that there is insufficient airflow to begin combustion. In this scenario, the motor might still be spinning, but not fast enough to close the sail switch.

Fair warning: This is difficult to diagnose as a DIYer. A furnace shutting down after its initial period can also be caused by the following:

• Bad sail switch
• Failing control board or motor relay
• Loose wire connections
• Stuck high-temperature limit switch
• Low incoming voltage (wiring, fuse, converter, etc.)

>>> READ MORE: RV Furnace Not Turning On? RV Tech Says 7 Easy Tips!

Furnace Never Kicks On

If your furnace will not even “kick on,” that is, if the motor never starts spinning, that could be a result of a dead motor. For instance, if a motor has an open winding (normally caused by age, excessive heat, or moisture buildup), then the motor may not spin at all. In some cases, the motor may hum but not spin, and in other cases, it may spool up if spun by hand. 

Fair warning: What appears to be a “dead motor” can also be caused by the following:

• Bad sail switch
• Stuck high-temperature limit switch
• Loose wire connections or bad ground connection
• Failing control board or motor relay
• Low incoming voltage (wiring, fuse, converter, etc.)

In summary: As you can tell, there are any number of symptoms that can point to a failing motor. Without proper electrical diagnostics, you’ll be taking a shot in the dark. 

How to Replace a Dometic or Suburban RV Furnace Motor

If you’ve concluded that your furnace has malfunctioned due to a bad motor, you’ll need to replace the motor.

Order the Correct Part

RV furnace motors are not universal. Not only are they different sizes, but they also spin at different speeds for proper airflow.

You’ll need to know your RV furnace’s model number and serial number in order to call for a part number for the replacement motor. You can find this information on a sticker either on the motor housing or a sheet metal casing.

Most RV furnaces are made by one of two manufacturers: Dometic or Suburban. You can call your manufacturer to find out the part number for the motor. Then, you can choose to buy the motor locally or online. 

If you buy locally, then you can order a part through your local RV service center or dealership. Some common motors (such as for Suburban SF-30 furnaces) are kept on the shelf, but most are ordered as needed. If you buy online, you’ll probably be waiting longer, but online parts usually cost about 20-30% less.

Research How to Replace Your Particular Furnace’s Motor

Unfortunately, there’s no such thing as a Chilton repair manual for RVs. You won’t find any germane instructions in the User Manual of the RV or the furnace. However, if you can track down the Service Manual for your furnace, it should contain some basic instructions on replacing the motor.

Hopefully, your furnace has a full-size access door on the exterior sidewall of your RV. If not – if your manufacturer skimped and only installed a sidewall exhaust vent – then you’ll have to completely uninstall and remove your furnace to access the motor. At this point, unless you’re a glutton for punishment, I would be contacting your local RV service technician.

In some cases, such as for some Suburban furnaces, the motor can be removed only after pulling out the furnace core. In this case, again, I would be contacting your local RV service technician. Pulling out a furnace core usually requires breaking into the gas propane system, and that’s not something to mess around with.  

If, however, you’ve lucked out and your motor can be replaced simply by removing the exterior access door, unscrewing the motor housing, popping the taps, disconnecting a whole bunch of wires, pulling out the motor assembly, disassembling the fan wheels, and then doing everything in reverse (you did color-code every wire and categorize every screw, didn’t you?), then you’re in luck.