Diagnose and repair a cold room that is not holding temperature

You are a Refrigeration Technician holding a refrigerant handling licence.

Simulated workplaceIntermediate missionCAQA Voltline Electrical

What is going on

Merriwa Cold Storage's cold room 3 alarmed overnight at minus 12 degrees against a set point of minus 20 and frozen product is at risk. Job J-26-1184 is open and van V-05 with recovery unit RU-02 and scale SCL-01 is on site. Leak detector LD-03 is away for its reference check so LD-01 from the workshop is in the van. The system is an R404A condensing unit on the roof with an evaporator in the room. The site manager reports the condenser fans sounded loud last week and that the unit has been short cycling. The refrigerant handling log shows a flare joint on cold room 2 was repaired two weeks ago, but cold room 3 has no recent history.

Carla Ferreira, Refrigeration and Air Conditioning Manager
Subject: Merriwa cold room 3 not pulling down, product at risk

Merriwa's cold room 3 alarmed overnight at minus 12 against a set point of minus 20 and there is product at risk. Marco is on his way with van V-05 and recovery unit RU-02. I want you to take the lead on the diagnosis: work through the control circuit and the refrigeration side logically, follow the refrigerant recovery procedure if the system has to be opened, and record everything on the job J-26-1184, the refrigerant handling log and the commissioning sheet. Leak detector LD-03 is at calibration, so use LD-01 from the workshop.

Your brief

Diagnose the fault logically across the electrical control circuit and the refrigeration circuit, isolate safely before any electrical work, recover and recharge refrigerant only if the system must be opened, leak test and commission the repair, and record everything on the job, the refrigerant handling log and the commissioning sheet so that the customer and the business have a complete record.

Work through it

You do not need to do it all. Doing a few of these will show you what the work is like. Your ticks and notes stay on this device.

Read the refrigerant recovery, charging and leak testing procedure and the safe isolation procedure, and review job J-26-1184 and the refrigerant handling log history for the site.
Complete the job safety analysis for roof work at the condensing unit and for electrical isolation, and record the isolation points and test for dead when working on the control circuit.
Record the initial operating readings: suction and discharge pressures, superheat, subcooling, compressor current, condenser and evaporator fan operation and the controller status and alarms.
Work through the likely causes in order, such as condenser fan failure, iced evaporator, low charge from a leak, or a control fault, and record the evidence for and against each.
If the system must be opened, weigh the recovery cylinder, recover the refrigerant with RU-02, pressure test, evacuate and recharge by mass using SCL-01, recording every mass in the refrigerant handling log.
Leak test every joint with LD-01 after charging and record the result, then run the system and record the commissioning readings until the room is pulling down towards set point.
Update job J-26-1184 with the fault found, the repair, the parts used and the time, and check the instrument register confirms LD-01 and SCL-01 are in service.
Brief the site manager on the cause, the repair and any recommendation, and record the conversation on the job.

My notes: what did I enjoy, and what surprised me?

What someone in this role would produce

Completed job safety analysis with isolation record
Fault diagnosis notes with readings and reasoning
Refrigerant handling log entry with recovered and charged masses and leak test result
Test results and commissioning sheet with final operating readings
Updated job record with repair details and customer briefing

Printing this is a record of what you explored. It is not a certificate or a qualification.