Walk-In Cooler Fans Running but Not Cooling

When you can hear the evaporator fans running and feel air moving but the box keeps warming, the fans are only half the story. They move box air across the coil; the refrigeration system has to make that coil cold and carry the heat outside. This page works from what you can see and feel inside the box back to which part of that job has stopped.

Rule out defrost first

Most coolers held near 35°F use off-cycle (air) defrost: the compressor stops on schedule and the evaporator fans keep running so box air melts the frost off the coil. During that time you will see exactly this symptom, fans on and no cooling, and it is normal.

Heatcraft's Beacon II controller defaults to two air defrosts a day that end when the coil reaches 45°F, or after a 40-minute fail-safe. Electronic controllers normally show a defrost status (dEF on Beacon II), and mechanical time clocks show defrost windows on the dial. If a defrost is underway, wait for it to end and check again. If the problem lasts well past the defrost window, keep going.

Then check the condensing unit

Walk outside, or to wherever the condensing unit sits, and look and listen.

• Condensing unit silent: the problem is on the compressor side. Go to compressor not running.
• Condensing unit running: the system is trying. The causes below are what stop it from moving heat.

What's usually behind it

Read the coil

The evaporator coil is the most useful thing you can look at from inside the box. With a flashlight, and without touching anything:

Clean, dark fins and air that feels barely cool. The coil isn't getting refrigerant, or isn't getting enough. With the condensing unit running, suspect low charge, a restriction, or a valve that won't open. A technician will measure pressures and superheat to tell which.

Frost on only part of the coil, usually the first few rows or where the refrigerant enters. The coil is being starved, so only the first section gets cold. This is the classic low-charge or expansion valve (TXV) pattern. Heatcraft's installation manual notes that valves set at high superheat lower refrigeration capacity, which is exactly what a starved coil feels like from inside the box.

Solid white ice across the whole face. Air can't pass through, so the fans spin and move very little. This is an airflow and defrost problem as much as a refrigerant one; see evaporator coil frozen for the patterns and why it must never be chipped.

One fan stopped or iced. Reduced airflow lets the coil get colder and frost faster, and the box warms. See evaporator fan motor.

Low refrigerant and the valves

A walk-in doesn't use up refrigerant. If the charge is low, there is a leak. A system losing charge slowly cools a little less each week: run times stretch, the coil frosts unevenly, and eventually a hot day tips it over. Bubbles in the sight glass can mean low charge, but not always; the filter drier and sight glass page explains why a technician doesn't rely on it alone.

The expansion valve meters refrigerant into the coil based on superheat, the amount the refrigerant vapor warms above its boiling point before it leaves the coil. Heatcraft's general guideline is 6 to 10°F of superheat for systems designed at a 10°F temperature difference. A valve that sticks closed, has lost its sensing bulb charge, or sits behind a clogged strainer starves the coil even with a full charge.

On pump-down systems, a liquid line solenoid opens when the thermostat calls. A burned-out coil or stuck valve keeps refrigerant from reaching the evaporator, and the compressor may cycle on and off on its low-pressure control while the box warms.

Some controllers report the result rather than the cause. Russell's EcoNet controller raises A108, "Cooler/Freezer not Satisfying Setpoint," when a cooling cycle runs past its run-time alert (120 minutes by default). Heatcraft's controllers raise a high box temperature alarm (A1 on Beacon II, BOXHI on the Smart Controller, AL01 on intelliGen).

The condenser side

Heat removed from the box has to be dumped outside at the condenser. If the condenser coil is caked with dust, grease or cottonwood, or its fan has stopped, pressure and temperature on the high side climb and cooling capacity drops. The fans inside keep running normally the whole time. The site's article on why cleaning condenser coils matters explains the mechanism, and the hub's condenser coil page covers safe cleaning.

Checks staff can do safely

1. Check the controller for a defrost status or alarm, and note any code exactly.
2. Confirm the condensing unit is running. If not, switch to the compressor page.
3. Feel the air leaving the evaporator with the back of your hand, keeping fingers away from the fan guard. Is it clearly colder than the room, or about the same?
4. Look at the coil with a flashlight and note the frost pattern: none, partial or solid.
5. Count the fans. Note any that are stopped, slow, iced or noisy.
6. Clear the airflow. Move product that is stacked against the front of the evaporator or blocking its discharge.
7. Look at the condenser for dirt and check its fan is turning. Cleaning happens only with the disconnect off, as the condenser page describes.

Safety: Keep hands and tools away from fan guards; the fans can start at any time when the controller calls. Do not add refrigerant, adjust valves, or jump the solenoid or controls to force cooling.

What a technician will check

• Suction and discharge pressures, superheat at the evaporator, and subcooling at the condenser.
• Whether the solenoid opens on a call for cooling, and whether the expansion valve responds.
• Temperature drop across the filter drier, which reveals a restriction.
• Condenser coil condition, condenser fan operation and head pressure.
• Evaporator fan motors, rotation and blade condition.
• Defrost settings and termination if frost patterns suggest weak defrost.
• A leak search if the charge is low, before any refrigerant is added. Only an EPA Section 608 certified technician may open the circuit.

Related symptoms

If the box does cool but never shuts off, see runs constantly. If the fans are running and water is blowing out of the unit, see evaporator dripping or spitting water. For Heatcraft equipment specifically, the site's Heatcraft troubleshooting guide has model-family notes.