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newSchoolWorks.com › VoTechWorks › Business & Cross-Cutting › Appliance Repair › Capstone Project: Full-Scope Appliance Diagnosis, Repair, and Documentation › Lesson 2
BUS-APPL73-08 · Lesson 2 · 54 clock hours · lab

Supervised Fault Diagnosis and Repair Execution

Objective. Students independently diagnose each assigned appliance using systematic test procedures, perform the necessary repair, and record all measurements, part numbers, and observations in real time on the standardized service order.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a credentialed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Overview

This lab session is the centerpiece of your capstone project. You will work through a set of instructor-staged faulty appliances from start to finish — diagnosis, repair, function test, and paperwork — without step-by-step prompting. The goal is to demonstrate that you can perform the complete service cycle the way an employer or a customer will expect it in the field.

Lockout/Tagout Before Anything Else

Before you touch any appliance, establish lockout/tagout (LOTO). Disconnect the power supply, apply your personal lock to the disconnect or plug lockout device, and verify zero energy with your meter. For gas appliances, close the supply valve and confirm with a combustible gas detector or soapy-water test that the line is isolated. For sealed-system work, note that the refrigerant circuit is a pressurized system even when the unit is unplugged — handle recovery and recharge equipment only after LOTO is complete for the electrical side. LOTO is not optional; an instructor intervention for skipping it is a file notation and a required restart of that appliance's sequence.

PPE for this lab: safety glasses at all times, insulated gloves when measuring live voltage (only after LOTO is released for a powered test), and cut-resistant gloves when handling sheet-metal panels or condenser coils.

The Diagnostic Sequence

Work systematically. Random probing wastes time and produces unreliable data. Follow this order for each appliance:

1. Visual inspection — Look for obvious faults: burned terminals, melted insulation, broken mechanical linkages, blocked airflow, signs of moisture or rodent damage. Record every observation on the service order before you move on.

2. Reference the wiring diagram — Identify the circuit path for the symptom reported. Locate test points.

3. Voltage measurements — With LOTO released only for powered testing and appropriate PPE on, verify that supply voltage is present and correct at the unit's terminal block. Then trace voltage to suspect components.

4. Resistance and continuity checks — With LOTO applied and capacitors discharged, measure component resistance. Compare readings to OEM specifications in the service manual. A motor winding reading of infinite ohms (open) or near-zero ohms (shorted to ground) is a clear failure indicator.

5. Temperature measurements — For refrigeration and HVAC-adjacent appliances, measure actual temperatures and compare to published operating ranges.

6. Pressure readings — For sealed-system work covered under your EPA 608 Type I certification, connect the manifold gauge set following safe handling procedures, read suction and discharge pressures, and compare to the manufacturer's charging chart for the specific refrigerant in use.

Record every measured value — numbers, not words like "low" or "high." The service order requires actual figures with units.

Confirming the Root-Cause Component

After completing your test sequence, write your diagnosis on the service order: the specific component that failed, the failure mode (open winding, shorted capacitor, stuck mechanical part, refrigerant undercharge, etc.), and the measurement that proves it. Bring this to the instructor for sign-off before you begin the repair. The sign-off step exists because an incorrect diagnosis leads to an unnecessary part replacement — a real cost in the field and a failing mark here.

Performing the Repair

Replace or correct only what the diagnosis identified. Follow OEM procedures for component removal and installation. Torque fasteners to specification where called out. When splicing or reconnecting wiring, use the connector type specified — no bare wire-nut substitutions on high-vibration appliances. For refrigerant procedures, recover existing refrigerant with EPA-compliant recovery equipment before opening the system, recharge to the weight or pressure specification on the nameplate or service manual, and document refrigerant type, amount recovered, and amount recharged on the service order. Venting refrigerant is illegal under Section 608 of the Clean Air Act and will result in immediate removal from the lab.

Function Test

Restore power in reverse LOTO order. Run the appliance through a complete operating cycle and measure the parameter that confirms correct operation — outlet temperature, amperage draw, pressure reading, cycle time, or whatever the manufacturer specifies as the acceptance standard. Record the measured value and the published specification side by side on the service order, then mark pass or fail. If the result fails, re-apply LOTO and go back to your diagnostic step.

Completing the Repair File

For each appliance, after the function test passes, complete the repair-file section:

Date and sign every section before moving to the next appliance. Unsigned entries are incomplete entries.

Key terms10

Lockout/Tagout (LOTO)An OSHA-required procedure that isolates all energy sources of a machine and secures them with a personal lock and tag before service work begins, preventing accidental re-energization.
Root-cause componentThe single failed part or condition that initiated the appliance malfunction, identified through systematic testing rather than assumption.
Function testA post-repair operational check in which the appliance is run through a full cycle and measured values are compared against manufacturer-published specifications to confirm the repair was successful.
Manifold gauge setA set of pressure gauges and hoses used to measure suction-side and discharge-side refrigerant pressures in a sealed refrigeration system.
Flat-rate labor estimateA predetermined labor charge for a specific repair task, expressed in standard hours and multiplied by the shop's hourly labor rate, used to price repairs consistently regardless of actual time spent.
Service orderThe standardized document used to record all diagnostic measurements, parts used, labor performed, test results, and customer-facing information for a single repair job.
EPA Section 608 certificationFederal certification required by the U.S. Environmental Protection Agency for technicians who purchase, handle, recover, or recharge refrigerants covered under Section 608 of the Clean Air Act.
Refrigerant recoveryThe process of removing refrigerant from a sealed system into an approved recovery cylinder using certified equipment, required before opening the system for repair; venting is prohibited by federal law.
Winding resistanceThe measured ohmic resistance of a motor or compressor winding, compared against OEM specifications to determine whether the winding is intact, open, or shorted.
Annotated wiring diagramA wiring diagram on which the technician has marked the location and identity of the identified fault, used as part of the permanent repair record.

Worked examples4

1. Your multimeter reads 4.2 Ω on the run winding and infinite (OL) on the start winding of a single-phase motor. The OEM service manual specifies run winding: 3.8–4.6 Ω, start winding: 9.2–10.8 Ω. What is your diagnosis and what is the measured deviation on the start winding?
  1. Compare run winding reading (4.2 Ω) to spec (3.8–4.6 Ω): 4.2 Ω is within range — run winding is acceptable.
  2. Compare start winding reading (infinite / OL) to spec (9.2–10.8 Ω): infinite ohms indicates an open circuit — the winding is broken.
  3. Deviation: the start winding reads infinite Ω versus a maximum specification of 10.8 Ω, which is a clear open-winding failure.
  4. Record on service order: 'Start winding — measured OL (open); spec 9.2–10.8 Ω. Root cause: open start winding. Motor requires replacement.'
Answer: The start winding is open (reads OL vs. spec 9.2–10.8 Ω). The run winding is within spec. Root-cause component: failed motor start winding — motor must be replaced.
2. A technician recovering R-134a from a household refrigerator records 0.45 lb recovered. After repair, the nameplate specifies a charge of 0.60 lb. How many ounces of R-134a must be added to reach the nameplate charge, and what is the deficit as a percentage of the nameplate charge?
  1. Calculate deficit in pounds: 0.60 lb − 0.45 lb = 0.15 lb.
  2. Convert deficit to ounces: 0.15 lb × 16 oz/lb = 2.4 oz.
  3. Calculate percentage deficit: (0.15 lb ÷ 0.60 lb) × 100 = 25%.
  4. Record on service order: 'Recovered 0.45 lb R-134a. Nameplate charge 0.60 lb. Added 2.4 oz (0.15 lb). System is 25% undercharged prior to recharge.'
Answer: Add 2.4 oz (0.15 lb) of R-134a. The system was 25% undercharged relative to the nameplate specification.
3. A shop charges $95.00 per flat-rate hour. The flat-rate guide lists a dryer heating element replacement at 0.8 hours. The replacement element costs $38.50 from the supplier catalog. What is the total quoted repair price (parts + labor)?
  1. Calculate labor charge: 0.8 hours × $95.00/hour = $76.00.
  2. Parts cost from catalog: $38.50.
  3. Total repair price: $76.00 + $38.50 = $114.50.
  4. Record on service order: 'Labor 0.8 hr @ $95.00/hr = $76.00. Part: heating element $38.50. Total: $114.50.'
Answer: Total quoted repair price is $114.50 ($76.00 labor + $38.50 parts).
4. During a function test of a refrigerator, you measure a fresh-food compartment temperature of 42 °F after a 20-minute stabilization run. The manufacturer specifies 35–38 °F at the default thermostat setting. By how many degrees Fahrenheit is the compartment out of specification, and is it high or low?
  1. Identify the specification upper limit: 38 °F.
  2. Measured value: 42 °F.
  3. Calculate deviation: 42 °F − 38 °F = 4 °F above the upper specification limit.
  4. Record on service order: 'Fresh-food temp measured 42 °F; spec 35–38 °F. Result: FAIL — 4 °F above upper limit. Return to diagnostic step.'
Answer: The compartment is 4 °F above the upper specification limit (42 °F vs. 38 °F max). The function test fails; the student must re-apply LOTO and return to the diagnostic sequence.

The math in this lesson1

Learners compare winding readings, 4.2 Ω and OL, to 3.8–4.6 Ω and 9.2–10.8 Ω specs.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Students work through each appliance in their fault set: establish LOTO, perform visual inspection, run the appropriate test sequence (voltage measurement, resistance checks, temperature measurement, pressure readings where sealed-system work applies), record all data on the service order form, and identify the root-cause component — instructor circulates and intervenes only for safety violations or when a student is stopped for more than fifteen minutes without progress, logging any intervention on the student's file. · Upon confirming diagnosis with instructor sign-off, student completes the repair (component replacement, wiring correction, refrigerant procedure under EPA 608 Type I rules as applicable), performs a function test of the repaired appliance against the manufacturer's normal operating specifications, and records pass/fail result with measured values. · After each appliance is repaired and function-tested, student completes the repair-file section for that unit: annotated wiring diagram with fault location marked, parts cost from current supplier catalog, flat-rate labor estimate, warranty notation, and a three-to-five sentence customer-facing repair summary written in plain language — all entries are dated and signed before moving to the next appliance.
Materials: Assigned faulty appliances (instructor-staged or student-sourced with approval), digital multimeter, clamp meter, manometer set, refrigerant recovery/recharge equipment (EPA-compliant), thermometer, wiring diagram binder, OEM service manuals, service order forms, parts catalog (current supplier), PPE kit (safety glasses, insulated gloves, cut-resistant gloves), LOTO kit, EPA 608 Type I reference card
Check: Instructor spot-checks each completed service order at the function-test stage; pass standard is that measured test values are recorded (not estimated), the identified fault matches the staged fault confirmed by instructor key, and the function-test result meets the manufacturer's published specification — any discrepancy requires the student to repeat the diagnostic step before proceeding.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Safety and Trade Practices
1. Before performing resistance checks on a motor winding, a technician must:
Diagnosis and Repair
2. A technician measures infinite (OL) ohms between the common and start terminals of a compressor motor. This reading most likely indicates:
EPA 608 / Refrigerant Handling
3. Under EPA Section 608 of the Clean Air Act, a technician who intentionally vents a regulated refrigerant to the atmosphere during an appliance repair:
EPA 608 / Refrigerant Handling
4. During a refrigerant recharge, the correct charge quantity is found by:
Diagnosis and Repair
5. A function test of a repaired appliance fails when the measured value does not meet the manufacturer's specification. The correct next step is to:
Professional Documentation
6. When recording measured values on a service order, a technician should:
Business and Estimating
7. A flat-rate labor guide lists a specific repair at 1.5 hours and the shop's labor rate is $90.00 per hour. The required part costs $47.25. What is the total quoted repair price?
Professional Documentation
8. A customer-facing repair summary in a service order should be written:
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