Count the fans
The first and most useful thing to do is stand in the box and count how many fans are actually spinning against how many there are. Multi-fan coils are normal on anything but the smallest walk-in, and a single stopped fan produces no dramatic symptom at all — just a box that does not hold quite as well as it used to and a patch of ice that keeps coming back in the same place.
We have found coils with two of four fans dead in boxes whose owners were convinced they had a refrigerant problem.
What fans actually do
Refrigerant boiling in the coil absorbs heat, but only from air that physically touches the fins. No airflow means the coil gets very cold and the box stays warm, and the moisture in the box deposits on that unnaturally cold coil as ice. So a fan failure produces two symptoms simultaneously: poor cooling and ice. People usually report the ice, and the ice sends them looking at the defrost system when the actual fault is a motor.
The causes
Motor failed
Bearings seize or windings go open. The clue is often a motor that is hot to the touch but not turning, or one that hums without starting. Shaded-pole motors, which are what most older coils use, run hot and have a limited service life in continuous cold damp duty.
Blade fouled or loose
Ice buildup can physically jam a blade against its guard, and if the motor then burns out you have two faults instead of one. Blades also work loose on their shafts and spin without moving much air.
Fan delay stuck
After defrost the fans are deliberately held off until the coil is cold again. If that delay control fails closed, the fans never restart. The symptom is distinctive: everything was fine, then after a defrost cycle it was not.
Defrost circuit holding them off
If the system believes it is permanently in defrost, the fans stay off by design. The coil will be warm rather than cold in this case, which distinguishes it immediately from a motor failure.
Thermal overload cycling
A motor drawing too much current trips its internal overload, cools, restarts, and does it again. You will see the fan running intermittently rather than not at all, which is a motor on its way out.
The upgrade worth knowing about
When a shaded-pole evaporator fan motor fails, it can usually be replaced with an electronically commutated motor instead. They use substantially less power, run cooler, and last considerably longer in this duty. On a coil with four fans running continuously, the energy difference is real money over a year and the replacement interval stretches out. It is one of the few genuinely worthwhile upgrades available during an ordinary repair, and we will quote both options rather than assuming.
What you can check
- Count spinning fans against total fans.
- Is the coil cold? Cold coil plus stopped fans is a motor or delay fault. Warm coil plus stopped fans means the system thinks it is in defrost.
- Is there ice specifically behind the stopped fan? That confirms it.
- Is a blade physically jammed by ice or fouling? Visible without tools.
Do not reach into a coil to free a blade with the power on. The fan will start the moment it releases.
Why this is a cheap call
Evaporator fan motors are inexpensive parts and the work is straightforward. Of everything on this index, this is one of the faults where calling early genuinely saves money — because a box run for months with a dead fan ices repeatedly, gets diagnosed as a defrost problem, and sometimes gets charged with refrigerant it never needed.
Questions we get asked
Should the fans run all the time?
On most walk-in coolers, yes, continuously, because constant air circulation keeps the box temperature even. On freezers they stop during defrost and restart after a delay that lets the coil get cold again, so that warm air is not blown over product.
One of my three fans has stopped. Does it matter that much?
Yes. You have lost roughly a third of the airflow over the coil, so capacity falls and the section of coil behind the dead fan will start to ice because nothing is moving air across it. It also loads the remaining motors harder.
Why do evaporator fan motors fail so often?
They run continuously in cold damp air, which is hard on bearings and on windings. Shaded-pole motors in particular have a finite life measured in a few years of continuous duty. Replacing them with electronically commutated motors lasts longer and uses markedly less energy.