08/15/2024 - I had been dispatched to investigate the freezer and instructed to pick up a tank of R-404A en route to the job. After I had set up my probes on the freezer, I found the suction superheat at the condenser was 62 degrees. I did not measure any pressure drop from the inlet of the suction line filter-drier and subcooling was only 1 degree. Suction pressure is very low, and the TD is more than 26 degrees; DTD for walk-in refrigeration equipment is generally 10 +/-3 degrees. The sight glass at the outlet of the liquid line filter drier is difficult to see into, and the moisture indicator is black. I added 4 pounds of R-404A until subcooling reached 9 degrees, and the suction line pressure / superheat measurement did not change. There is a liquid line restriction, likely a failed TXV - the line driers, and sight glass should be replaced along with the valve. I suspect the very small size of the freezer box is saving the product, as it appears low airflow across both coils is reducing cooling capacity. The differential control mounted to the evaporator appears to be working correctly, but it is set higher than every other walk-in freezer I've serviced at +10 degrees. When I went inside to check the freezer box temperature, the kitchen staff informed me that it was the walk-in cooler that wasn't working properly. I informed them I'd be checking both systems - I'll make a separate service inspection report for the cooler for the sake of clarity.
Recommendations:
Replace the TXV, liquid line drier with sight glass, and suction line drier.
While the system is offline, the evaporator and condenser coils should be thoroughly cleaned.
After these repairs, the system would need to be recommissioned.
Given the labor involved in this repair, it might make sense to offer repair vs replacement quotes.
08/15/2024 - On arrival, the cooler box was 42 degrees and I measured a 1.5-degree delta-T. The mechanical thermostat was set to 35, but shut the system down at 40 degrees. I lowered the setpoint to 30 for now to offset the drift in accuracy of this component. The walk-in cooler's sight glass at the outlet of the liquid line drier was full of vapor and liquid refrigerant. When I removed the caps on the access ports, the liquid line schrader valve started spewing refrigerant so I replaced it before taking measurements. I measured a 2.3 PSIG drop from the inlet of the suction line drier and the suction access port of the condenser - anything over 1 PSI is considered unacceptable. I added 5 pounds of R-22 to the system - 4 pounds to achieve a clear sight glass plus a pound to make sure the receiver had enough liquid refrigerant inside. I then measured a delta-T of 2.6 across the evaporator. Suction pressure is still low, Superheat is high (44 degrees), condensing pressure is high, the evaporator is visibly filthy, and there are likely more leaks in the system.
Recommendations:
A leak search should be done to determine where several pounds of R-22 left the system.
To regain cooling capacity for this system, we would need to replace the TXV, line drier with sight glass, and suction line drier.
The mechanical thermostat should also be replaced – I recommend the Ranco ETC-111000-000 digital temperature control.
The coils would also have to be cleaned, and the system recommissioned.
Given the labor involved in this repair, it might make sense to offer repair vs replacement quotes.
