Fridge Compressor Runs but No Cooling Decision Tree

Why this matters

A running compressor with no temperature drop is the highest-stakes call in residential refrigeration because it forks into either a 20-minute repair or a sealed-system condemnation that triggers a buy-vs-fix conversation with the customer. The wrong branch costs the customer a fridge or costs the shop a callback. Most techs default to "low charge" the moment they feel a warm box, which is the single most common misdiagnosis on dual-evaporator French door units. The decision tree below forces airflow and defrost checks ahead of the sealed-system call so the tech does not vent refrigerant on a $20 fan motor problem. ASHRAE Handbook (Refrigeration, 2022) and the Sub-Zero / Whirlpool / LG service manuals all converge on the same isolation order.

Symptom presentation at the door

Confirm the customer report before opening the unit. Ask: how long since cooling stopped, was it gradual or sudden, has anyone unplugged or moved the unit, and is the freezer also warm or only the fresh-food side. Sudden total loss with both compartments warm points at the compressor, start components, or main control board. Gradual warming over days with the freezer still partially cold points at airflow, defrost, or low charge. Only the fresh-food side warm on a top-mount or French door points at the damper, evap fan, or defrost system, not the compressor.

Place a calibrated thermocouple in each compartment before opening any panel. Record the readings. If freezer is at or below 10 F and fresh food is at 50 F, the sealed system is fine and the issue is air movement or damper control. If both compartments are above 50 F after 12 hours of runtime, suspect sealed system, condenser airflow, or main control.

Quick checks before pulling panels

Listen at the compressor. A steady hum with no clicking and a warm-to-hot shell after 10 minutes of runtime means the compressor is rotating. A clicking every 3 to 5 minutes with no sustained run is a start-component or locked-rotor symptom and belongs in a separate decision tree, not this one.

Feel the condenser. A discharge line that warms within 2 minutes and a condenser coil that reaches at least 20 F above ambient confirms the compressor is moving refrigerant. A cold or barely warm condenser with a running compressor points at zero charge, valve failure inside the compressor, or a blocked cap tube.

Pull the kick plate and check the condenser fan. On bottom-mount and French door units the condenser fan runs whenever the compressor runs. A stopped condenser fan will push head pressure high, the compressor will short-cycle on its overload, and the box will warm. Spin the fan by hand; if it binds or shows blade damage, replace before going further.

Check the gasket. A gasket that has lost magnetic pull or shows a visible gap will not by itself cause "no cooling," but on a unit that has been worked on twice already, a failed gasket is the silent driver of a "runs constantly, never gets cold" callback. Cull this confounder early.

Isolation tree by compartment pattern

Branch A: freezer cold, fresh food warm. Pull the rear fresh-food panel and look at the damper. On Whirlpool side-by-side and French door units the damper is a stepper-driven assembly that fails open or closed depending on firmware state. Manually cycle the damper from the diagnostic mode (Whirlpool: hold the door switch and press the freezer-temp-up button per the service-manual sequence on the model tag). If the damper does not move, replace the damper assembly. If the damper moves but the fresh-food evap fan does not run, replace the evap fan. If both run, suspect the thermistor on the fresh-food side reading low.

Branch B: both compartments warm, freezer warmer than fresh food. This is unusual and almost always points at defrost system failure on a single-evap unit. Check the evaporator behind the freezer rear panel. A solid ice block over the coil that does not let air through confirms a stuck defrost cycle. Test the defrost heater for continuity (typical glass-tube heater reads 20 to 40 ohms; sheath heaters read 8 to 25 ohms; consult the model service sheet). Test the defrost thermostat or bimetal in a freezer for closed continuity. Test the defrost control board or main board for the timed defrost cycle by initiating forced defrost from diagnostic mode. Replace the failed component.

Branch C: both compartments warm, condenser cold or barely warm, compressor humming. This is the sealed-system fork. Confirm by hooking a sealed-system process tube or a piercing valve only if you intend to recover and recharge. Do not pierce a high-side or low-side line on an inverter unit without first reading the OEM procedure; the LG inverter linear-compressor units in particular have specific charge and process port specifications. If the unit holds vacuum and pulls down on recharge but warms again within 24 hours, the leak is in the box and the unit is a candidate for condemnation. If the compressor runs but no refrigerant is moving (no temperature differential across the cap tube), the compressor is mechanically failed or the suction valve is leaking internally; condemn the sealed system.

Confirming the diagnosis before parting

For airflow and damper calls, run the unit for 4 hours after the repair with a thermocouple in each compartment. Document the pull-down curve. Fresh food should hit 38 F within 4 hours of an empty restart; freezer should hit 0 F within 6 hours.

For defrost calls, run a forced defrost cycle from diagnostic mode and confirm the coil clears in the rated time (typically 18 to 32 minutes on residential units). Confirm the bimetal opens at the correct temperature on a second cycle.

For sealed-system calls, recover refrigerant per EPA Section 608 (40 CFR Part 82, Subpart F), pull a deep vacuum to 500 microns and confirm the vacuum holds for 30 minutes with the pump isolated. Charge by weight to the data plate spec. Run the unit for 12 hours and verify pull-down. A unit that holds vacuum but loses charge within a week has a slow leak in a brazed joint or the evaporator and is generally a condemn.

Remediation paths

Repair paths: condenser fan motor, evap fan motor, damper assembly, defrost heater, defrost thermostat, main control board, thermistor harness. All are non-sealed-system parts. EPA 608 is not required to swap any of these.

References

• EPA Section 608 of the Clean Air Act, 40 CFR Part 82, Subpart F (Refrigerant Management Regulations).
• DOE 10 CFR Part 430, Subpart B, Appendix A1 (Uniform Test Method for Measuring the Energy Consumption of Refrigerator-Freezers).
• ASHRAE Handbook, Refrigeration (2022 edition), Chapter 17 (Household Refrigerators and Freezers).
• Whirlpool / Sub-Zero / LG service-manual diagnostic mode entry tables on the model tag inside the unit.
• ANSI / AHAM HRF-1 (Energy and Internal Volume of Refrigerating Appliances).