Think you need to replace your AC fan motor? Maybe not


By Steve Savage, Mobility RV Service

It’s warm out and air conditioners are humming — or should be. Then comes the request for service. A common one concerns air delivery, or more specifically, “My air conditioner is not blowing as hard as it should,” or “My air conditioner fan will not start.” Before getting in line for service, let’s talk about possible problems.

Let’s take the “fan motor won’t start at all” first.Air conditioners sit for months without running and one of the things that often happens during that time is the motor shaft rusts and sticks in the bushing. Before ordering a new motor, try freeing the motor shaft by turning it by hand. In severe cases you may need pliers. Do this while the unit is off (OK, sometimes I do it with the fan switched on, but that is me). What you will often discover is once the shaft is freed up and the motor starts to run, the problem goes away.

I do this dozens of times each year on dealer lots. If you call me on the phone (customers only, not Internet readers), I will discuss this possibility with you before I fire up the truck and charge a bushel of money for a very simple and brief fix. I have run into this so often, I have made a bent hook out of a piece of aluminum trim and don’t even have to unscrew the cover in order to get it spinning. In my experience, the problem is more common with Dometic Duo Therms rather than Colemans, but they all do it some.

Next up is “air delivery at the vents is too weak.” Again, this is not a motor replacement issue, at least in my experience. More likely than not, your coil is “iced.” When humidity is high, running the fan on high is often the cure to put more heat across the evaporator coil. That’s the coil you can see from inside the camper, and if you drop the filter cover and look up, you often can see the ice. If running the fan on high does not cure the problem, your freeze control that is sticking in the coil and is designed to shut off the compressor when the coil starts to freeze may have been left out or has fallen out of the coil.

Sometimes the freeze control does fail. The good news is, it is not an expensive part and takes only a few minutes to take out the old one and plug in the new one. Duo Therms are a normally open circuit and Coleman’s are normally closed, so they are not interchangeable and can be tested for continuity to ensure one is not replaced unnecessarily. I replace less than one a year, so failure is uncommon.

Do fan motors fail? Sure, but not often. If you know how to use a multimeter to test an electric motor, you already know how to check them. In my opinion, Coleman’s are the easiest to replace, Duo Therms are not bad, and I hate replacing Penguin motors. As always, be sure to diagnose before ordering a motor!