System Commissioning, Testing, and Troubleshooting

Commissioning, Testing, and Troubleshooting of Systems

Introduction to Commissioning

Commissioning is the set of systematic operations used to verify that a refrigeration or air conditioning system is installed, adjusted, and operational in accordance with the designer's specifications and the requirements of applicable codes. For the Red Seal exam, you must master the logical sequence of these operations, measuring instruments, performance calculations, and diagnostic methods.

Commissioning is not limited to starting the system. It includes: installation verification, leak testing, evacuation, refrigerant charging, adjustment of control devices, verification of safety controls, and documentation of results.

Commissioning Sequence

Preliminary Checks Before Start-Up

Before any power-up or refrigerant charging, you must perform a complete visual inspection:

Verify the tightness of electrical connections (torque according to manufacturer's specifications)

Check the continuity of control circuits

Ensure that circuit breakers and fuses are sized according to the drawings

Verify pulley alignment and belt tension

Confirm that pipe supports are in place and that the piping is free from stress

Inspect welds and joints for visible defects

Important: The Canadian Electrical Code, Part I, Rule 8-200 requires that a notice of installation be submitted to the authority having jurisdiction before initial energization. This applies to permanent installations.

Leak Testing of the Refrigeration Circuit

The leak test must be performed with dry nitrogen (N₂) or a mixture of nitrogen and trace refrigerant. The test pressure must never exceed the maximum working pressure of the low-pressure side or the high-pressure side, depending on the side being tested.

Component	Typical Test Pressure (R-134a)	Typical Test Pressure (R-410A)
Low-pressure side	1,200 kPa (174 psig)	2,500 kPa (363 psig)
High-pressure side	2,000 kPa (290 psig)	4,100 kPa (595 psig)
Minimum test duration	30 minutes	30 minutes

Test Procedure:

20.Pressurize the circuit with nitrogen to approximately 70% of the final test pressure

21.Wait 10 minutes to allow for thermal equalization

22.Complete pressurization to 100%

23.Record the pressure and ambient temperature

24.Wait 30 minutes and compare readings

25.A pressure variation due to temperature is normal: use the correction formula

Pressure Correction Formula:

P₂ = P₁ × (T₂ + 273) / (T₁ + 273)

Where P₁ and T₁ are the initial pressure and temperature, and P₂ and T₂ are the final values. A pressure drop greater than 1% after correction indicates a leak.

Leak Detection

After the nitrogen leak test, if a leak is detected, it must be located. Detection methods include:

Soap solution: effective for large leaks, apply to joints, welds, and fittings

Electronic leak detector: sensitive to halides, calibration required before use

UV lamp with dye: inject the dye after charging, then inspect with the lamp

Ultrasonic leak detector: detects leaks by the sound emitted by gas under pressure

Exam Trap: Never use oxygen or acetylene to pressurize a refrigeration circuit. Oxygen reacts with refrigerant oils and can cause an explosion. Use only dry nitrogen.

Evacuation of the Circuit

Principles of Evacuation

Evacuation removes moisture and non-condensable gases from the circuit. Residual moisture can cause acid formation, expansion valve freezing, and oil degradation.

Evacuation Requirements:

Final micron level: 500 microns or less (ideally 300 microns)

Minimum duration: 30 minutes after reaching the target micron level

Use a two-stage vacuum pump for systems larger than 5 tons

Evacuation Procedure

44.Connect the vacuum pump to both service ports (suction and discharge) if possible

45.Fully open the vacuum pump valves

46.Start the pump and record the initial micron level

47.Continue until 500 microns is reached

48.Close the pump valve and perform the vacuum rise test

49.If the pressure rises more than 100 microns in 10 minutes, there is a leak or residual moisture

Vacuum Rise Test: After reaching 500 microns, close the pump isolation valve. Wait 10 minutes. If the reading exceeds 600 microns, there is a problem.

Exam Trap: Never use the system compressor to perform the vacuum. This would damage the compressor and would not produce a sufficient vacuum.

Refrigerant Charging

Charging Methods

Method	Application	Advantages	Disadvantages
Liquid charging (liquid line)	New systems, large capacity	Fast, accurate	Risk of liquid slugging to the compressor
Vapor charging (suction side)	Small systems, topping up charge	Safe for the compressor	Slow, less accurate
Charging by weight	All systems	Maximum accuracy	Requires a scale
Charging by superheat	Thermostatic expansion valve	Adjusts charge according to conditions	Requires instruments

Charge Calculation

The nameplate charge is indicated on the equipment nameplate. For systems with long liquid lines, add 0.5% of the charge per meter of additional line beyond 7.5 m.

Calculation Example:

System with a nameplate charge of 4.5 kg of R-410A. Liquid line of 15 m.

Excess length: 15 m − 7.5 m = 7.5 m

Addition: 7.5 m × 0.5% × 4.5 kg = 0.169 kg

Total charge: 4.5 kg + 0.169 kg = 4.669 kg

Indicators of Correct Charge

Evaporator superheat: 5°C to 8°C (thermostatic expansion valve)

Condenser subcooling: 5°C to 10°C

Compressor superheat: 10°C to 20°C (measured 15 cm from the compressor)

Air temperature differential: 8°C to 12°C for air conditioning

Adjustment of Control Devices

Thermostatic Expansion Valve (TXV)

TXV adjustment is done using the adjustment stem. Superheat is measured as follows:

Superheat = Suction line temperature − Evaporating temperature (corresponding pressure)

Adjustment Procedure:

72.Install a thermometer on the suction line near the bulb

73.Install a gauge on the low-pressure service port

74.Convert the pressure to saturation temperature (use the refrigerant chart)

75.Calculate the actual superheat

76.Turn the adjustment stem clockwise to increase superheat (reduce flow)

77.Wait 15 minutes between each adjustment to allow the system to stabilize

Reference Values:

Standard TXV: 5°C to 8°C

TXV with external equalizer: 4°C to 6°C

Capillary tube: 2°C to 4°C (not adjustable)

Pressure Switches and Safety Controls

Type of Pressure Switch	Typical Setting (R-404A)	Function
High pressure (HP)	2,800 kPa (406 psig)	Shutdown at maximum pressure
Low pressure (LP)	100 kPa (15 psig)	Shutdown at minimum pressure
HP differential	400 kPa (58 psig)	Automatic reset
LP differential	150 kPa (22 psig)	Automatic reset

Safety Rule: The high-pressure switch must be set to a value lower than the test pressure of the weakest vessel in the circuit. Consult the manufacturer's nameplate.

Water Regulating Valves (Water-Cooled Condensers)

Water valve: adjust to maintain a constant discharge pressure

Typical differential: 100 kPa to 150 kPa between opening and closing

Outlet water temperature: 35°C to 40°C for water-cooled condensers

Performance Testing

Energy Efficiency Calculations

Coefficient of Performance (COP):

COP = Cooling capacity (kW) / Power input (kW)

EER (Energy Efficiency Ratio):

EER = Cooling capacity (BTU/h) / Power input (W)

Conversion: 1 kW = 3,412 BTU/h

Example:

System producing 10.5 kW of cooling with a power consumption of 3.2 kW.

COP = 10.5 / 3.2 = 3.28

EER = (10.5 × 3,412) / 3,200 = 11.2 BTU/(W·h)

Airflow Measurement

Grid Method:

102.Measure air velocity with an anemometer at several points across the grille

103.Calculate the average velocity

104.Multiply by the effective area of the grille

Flow rate (m³/s) = Average velocity (m/s) × Effective area (m²)

Cone Method: Use a calibrated flow hood for exhaust grilles.

Pressure Drop Method: Measure static pressure across a clean filter and use the manufacturer's curve.

Condenser Heat Balance

Total heat rejected at the condenser:

Q_cond = Q_evap + P_comp

Where:

Q_cond = heat rejected (kW)

Q_evap = cooling capacity (kW)

P_comp = compressor power input (kW)

Example:

Q_evap = 10.5 kW, P_comp = 3.2 kW

Q_cond = 10.5 + 3.2 = 13.7 kW

Systematic Troubleshooting

Diagnostic Methodology

120.Gather information: customer complaint, maintenance history, ambient conditions

121.Visual inspection: look for oil leaks, ice, damaged components

122.Electrical measurements: voltages, currents, winding continuity

123.Refrigeration measurements: pressures, temperatures, superheat, subcooling

124.Analysis: compare measurements to theoretical values

125.Root cause verification: do not treat the symptom, but the cause

Quick Diagnostic Chart

Symptom	Possible Causes	Checks
Suction pressure too low	Insufficient charge, clogged filter, TXV under-adjusted	High superheat, low subcooling
Suction pressure too high	Excessive charge, TXV over-adjusted, inefficient compressor	Low superheat, high subcooling
Discharge pressure too high	Dirty condenser, air in the circuit, excessive charge	Condenser temperature differential
Discharge pressure too low	Oversized condenser, insufficient charge, faulty 4-way valve	Low subcooling
Compressor short-cycling	LP switch misadjusted, insufficient charge, blocked expansion valve	Run time, pressure switch differential
Excessive superheat	TXV under-adjusted, bulb poorly attached, insufficient charge	Suction line temperature
Zero superheat	TXV over-adjusted, detached bulb, excessive charge	Risk of liquid slugging

Compressor Diagnostics

Winding Resistance Test:

Motor Type	Terminals	Typical Resistance (Ω)
Single-phase (CSR)	C-R	2 to 5 Ω
Single-phase (CSR)	C-S	5 to 10 Ω
Three-phase	T1-T2, T2-T3, T1-T3	Equal to each other

Insulation Test: Use a megohmmeter (500 V) between each terminal and ground. The resistance must be greater than 1 MΩ.

Current Test: Measure the current of each phase. An imbalance greater than 10% indicates a supply or motor problem.

Current Imbalance (%) = (Max current − Min current) / Average current × 100

Thermostatic Expansion Valve Diagnostics

Signs of Failure:

TXV blocked closed: low suction pressure, high superheat, compressor short-cycling

TXV blocked open: high suction pressure, zero superheat, risk of liquid slugging

Loss of bulb charge: TXV closes completely, suction pressure drops

TXV Test:

140.Warm the bulb with your hand: the suction pressure should increase

141.Cool the bulb with ice: the suction pressure should decrease

142.If there is no reaction, the TXV is defective

Analysis of Operating Parameters

Superheat and Subcooling

Superheat: the difference between the actual vapor temperature and its saturation temperature at the same pressure. It ensures that refrigerant reaches the compressor in vapor phase.

Subcooling: the difference between the liquid saturation temperature and its actual temperature. It ensures that refrigerant reaches the expansion valve in liquid phase.

Formulas:

Superheat = Actual suction temperature − Saturation temperature (at suction pressure)

Subcooling = Saturation temperature (at discharge pressure) − Actual liquid temperature

Interpretation of Pressures

Compression Ratio:

Ratio = Absolute discharge pressure / Absolute suction pressure

Normal Values: 2.5 to 4.5 for single-stage compression systems. A ratio greater than 5 indicates a problem (excessive discharge temperature, reduced efficiency).

Discharge Temperature: Must not exceed 120°C for most compressors. Beyond this, the oil degrades and the compressor may fail.

Verification of Safety Controls and Protection Devices

Mandatory Safety Controls According to Codes

Canadian Electrical Code, Part I: requires grounding, overcurrent protection, disconnecting means

CSA B52: standard for mechanical refrigeration systems — requires safety relief valves, rupture discs, pressure switches

CSA B149.1: applicable if the system uses natural gas for a generator set or a burner

Safety Relief Valves

CSA B52 Requirements:

Install a safety relief valve on each pressure vessel

The valve must be sized to relieve the entire charge in case of fire

The discharge must be directed outdoors or to a safe location

Never install an isolation valve between the vessel and the relief valve

Typical Set Points:

Low-pressure vessel: 1,500 kPa to 2,000 kPa

High-pressure vessel: 2,500 kPa to 3,000 kPa

The set pressure must be lower than the test pressure of the vessel

Safety Pressure Switches

The HP switch must be manually reset for systems larger than 5 kW

The LP switch may be automatically reset if the system is protected against short-cycling

Verify the operation of pressure switches by simulating conditions (never block safety relief valves)

Operational Testing and Documentation

Complete Operational Test

176.Start-up: verify the start-up sequence, anti-short-cycle delay (5 minutes minimum)

177.Steady state: wait 30 minutes, then measure all parameters

178.Cycling: verify the operation of the thermostat or controller

179.Defrost (if applicable): verify the complete cycle, defrost termination temperatures

180.Safety controls: test each safety control individually

181.Shutdown: verify the shutdown sequence, pump-down cycle

Required Documentation

Commissioning report with all measurements

Leak test certificate (nitrogen test)

Evacuation report (final micron level)

Quantity of refrigerant charged

Pressure switch and safety control settings

Performance test results

Copy of the technician's qualification certificates

Summary

Commissioning follows a strict sequence: preliminary checks, leak testing, evacuation, charging, adjustments, performance testing

The leak test is done with dry nitrogen, never oxygen or acetylene

Evacuation must reach 500 microns or less, with a vacuum rise test

Refrigerant charging is done by weight for accuracy, with additions for long lines

TXV superheat must be 5°C to 8°C; subcooling must be 5°C to 10°C

The normal compression ratio is 2.5 to 4.5

Safety controls must be tested individually and documented

The Canadian Electrical Code, Part I, Rule 8-200 requires the notice of installation before energization

CSA B52 governs safety relief valves and pressure vessels

Pitfalls to Avoid

201.Confusing gauge pressure and absolute pressure in compression ratio calculations — always use absolute pressures (add 101.3 kPa to gauge pressure)

202.Using oxygen for leak testing — risk of explosion with oil; use only nitrogen

203.Forgetting the temperature correction during leak testing — pressure varies with temperature; use the correction formula

204.Charging liquid refrigerant into the suction side — risk of liquid slugging; charge vapor into the suction side or liquid into the liquid line

205.Not waiting for the system to stabilize between adjustments — wait at least 15 minutes after each adjustment

206.Confusing superheat and subcooling — superheat is measured on the low-pressure side, subcooling on the high-pressure side

207.Setting the HP switch above the test pressure — always check the manufacturer's nameplate

208.Forgetting the notice of installation (Rule 8-200 of the Canadian Electrical Code) before energization

209.Not testing safety controls after commissioning — each safety control must be verified individually

210.Using an uncalibrated leak detector — always calibrate according to the manufacturer's instructions before use

211.Ignoring three-phase current imbalance — an imbalance greater than 10% indicates a serious problem

212.Not documenting results — documentation is mandatory for traceability and warranty purposes

213.Confusing refrigerants when charging — check the nameplate and use the appropriate fittings (R-410A fittings are different from R-22)

214.Forgetting the anti-short-cycle delay — respect the minimum 5-minute delay before compressor restart