6.5.1 — Airside Checks

Actuators & Dampers

Motorised dampers control outside air, return air, exhaust, and zone air volumes. A sticking or incorrectly calibrated damper can waste enormous amounts of energy by admitting unconditioned air or blocking the required outside air for ventilation.

• Visually confirm damper blades move freely through full stroke (0–100 % open)
• Check actuator at both end stops; verify blade position matches actuator signal
• Lubricate linkage pivots with a dry or light oil lubricant where specified
• On DDC systems, command the damper open and closed from the controller and verify feedback signal matches commanded position
• Check blade edge seals for tears that allow air bypass in the closed position

Belts & Pulleys

Belt-driven fans require tension and alignment checks at every PM visit, and belt replacement on a schedule (typically annually or when showing wear). As covered in 6.4, use the deflection method to verify tension. At each PM:

• Inspect belt surface for cracking, glazing, fraying, or missing ribs (poly-V belts)
• Check sheave grooves for sharp edges or hourglass wear profile
• Verify sheave alignment with a straightedge across both faces
• Record belt deflection measurement and compare to previous PM
• Check belt guard is secure and clearances are adequate

Coil Condition Checks

Visual coil inspection at each PM allows fouling to be caught before it causes measurable capacity loss. Key checks:

• Shine a flashlight through both the evaporator and condenser coil — you should see light through the entire depth of the fin pack
• Check for bent fins near the coil edges; straighten with a fin comb where possible
• Note any oil streaks on the coil surface, which indicate a refrigerant leak at nearby joints
• Record coil condition (clean / light fouling / heavy fouling) on service record for trend tracking
• Measure entering and leaving air temperatures across the coil; compare to design ΔT

6.5.2 — Electrical Checks

Amperage Measurements

Motor amp draw is one of the most useful single measurements a technician can take. Record amperage for every motor (compressor, condenser fan, evaporator fan, pump) at every PM visit and compare to:

• Nameplate RLA/FLA: Current should not exceed FLA by more than 10 % under normal conditions
• Previous PM records: A gradual upward trend indicates bearing wear, capacitor degradation, or increasing mechanical load
• Other phases on three-phase motors: Imbalance of more than 10 % between phases indicates a supply or motor problem

Voltage Measurements

Measure and record supply voltage at the equipment disconnect (not at the panel) with the system running at full load:

• Single-phase: Measure L1–L2; verify within ±10 % of nameplate
• Three-phase: Measure all three phase-to-phase combinations; calculate imbalance (see 6.3)
• Control voltage: Verify 24 V ± 2 V at the control board with the system energised
• Record voltage drop across contactor contacts (<2 V is acceptable)

Visual Electrical Inspection

Before energising the system at the start of each PM, perform a visual electrical inspection with the disconnect open and locked out:

1. Check all wire terminations in the disconnect, contactor, control board, and motor terminal box for tightness and corrosion.
2. Look for discoloured insulation, melted plastic, carbon tracking, or burn marks.
3. Inspect capacitors for bulging tops, oil leakage, or cracked cases.
4. Check contactor contacts for pitting; verify contactor pulls in and releases cleanly.
5. Verify control board for obvious damage, corrosion, or burnt components.
6. Confirm all safety devices (high-pressure switch, low-pressure switch, freeze stat, flow switch) are wired in and not bypassed.

6.5.3 — Refrigerant & Leak Checks

Electronic Leak Detector Procedure

An electronic leak detector must be used systematically to find small leaks before they result in a measurable charge loss. Heated diode and infrared detectors are the most common types; follow the manufacturer’s warm-up and sensitivity requirements.

1. Start at the highest-risk locations first: flare fittings, brazed joints at the service valves, condenser coil headers, evaporator coil U-bends.
2. Hold the probe tip below the refrigerant circuit (refrigerant vapour is heavier than air for most HFCs).
3. Move the probe slowly (approximately 1 in./second) around each fitting and joint.
4. When the detector alarms, move the probe away and let it recover, then re-approach from multiple angles to pinpoint the exact leak source.
5. Mark any leak location found; repair before adding refrigerant.
6. Recalibrate the detector at fresh air before moving to the next circuit section.

Visual Leak Inspection

Many refrigerant leaks announce themselves visually before they cause measurable charge loss. Look for:

• Oil staining on brazed joints, flare fittings, or coil headers (refrigerant carries oil)
• Green or blue-white crystalline deposits around brass fittings (refrigerant reacting with copper oxide)
• Frosting on unexpected locations (liquid refrigerant flashing at a leak point)
• UV dye fluorescence under a UV lamp where UV dye has been previously installed

6.5.4 — Mechanical Checks

Fan Cycling & Controls

Condenser fan cycling controls modulate condenser capacity at low ambient temperatures to maintain adequate head pressure for TXV and metering device operation. At PM:

• Verify fan cycling switches cycle fans at correct pressure set points (typically Off below 200 psig, On above 280 psig for R-410A)
• On VFD-controlled condenser fans, verify speed modulates correctly with head pressure
• Check that all condenser fans run simultaneously at full load in warm weather
• On indoor air handlers, verify fan delay relay (fan runs briefly after cooling stops to remove residual moisture from coil)

Lubrication

Motors with grease fittings require periodic lubrication according to manufacturer schedules. Over-lubrication is as harmful as under-lubrication.

• Use only the manufacturer-specified grease type (typically a polyurea or lithium-complex bearing grease rated for the motor’s operating temperature)
• Never mix different grease types in the same bearing — incompatible thickeners can liquefy the grease
• Add grease slowly with the motor running if possible, until fresh grease emerges from the purge port
• Wipe up any expelled grease to prevent it from being drawn onto motor windings
• Many modern motors are permanently lubricated and require no field greasing — verify the motor nameplate or O&M manual before attempting to lubricate

Motor & Rotation Check

Verify correct rotation for all fans and pumps at every PM or after any electrical disconnect, motor replacement, or rewiring:

• Centrifugal fans: Correct rotation moves air toward the discharge outlet. Reverse rotation still moves some air but at greatly reduced volume and efficiency (typically 50–60 % of design CFM at much higher power draw).
• Axial (propeller) fans: Correct rotation is moulded into the blade — observe airflow direction and compare to design (condenser fans discharge upward; cooling tower fans discharge upward).
• Three-phase motors: Swap any two supply conductors to reverse rotation if needed.
• Scroll compressors: Are rotation-sensitive — reverse rotation causes immediate compressor damage. Verify phase sequence on three-phase scroll compressors at commissioning and after any rewiring.

Oil Levels (Open & Semi-Hermetic Compressors)

Open and semi-hermetic compressors have an oil sight glass on the crankcase. Check the oil level with the compressor running at steady state; the oil level should be visible in the lower half to two-thirds of the sight glass. Low oil level indicates:

• Oil logging in the evaporator (low suction velocity; oversized suction line)
• Oil carryover into the discharge line (worn rings; excessive crankcase pressure)
• Oil lost through leaks at shaft seals (open compressors)

Check oil colour: clean refrigerant oil is clear to light yellow. Brown or black oil indicates acid contamination or overheating. Test with an oil acid test kit; if acid is present, flush the system and replace the drier and oil charge.

Variable Frequency Drive (VFD) Operation

VFDs control fan and pump motor speeds to match load, providing significant energy savings at part load. PM checks for VFD-driven equipment:

• Check VFD display for fault codes and operating parameters (output frequency, current, voltage)
• Verify VFD enclosure cooling fan operates (VFDs generate heat internally)
• Check VFD input and output terminals for loose connections and corrosion
• Verify VFD operates through its speed range (minimum to maximum Hz) without faults
• Confirm bypass contactor (if installed) is not engaged in normal operation — a bypassed VFD runs the motor at full speed continuously, eliminating all energy savings
• Record VFD operating hours from the drive display and compare to previous PM

6.5.5 — Condensate Pump & Drain Checks

Condensate Pump

Where gravity drainage is not possible, a condensate pump lifts condensate to a suitable drain. At PM:

1. Pour water into the pump reservoir until the float triggers and the pump runs; verify water is discharged and the pump shuts off cleanly.
2. Check the pump reservoir for slime and algae; clean with dilute bleach solution.
3. Inspect the discharge line for kinks, obstructions, and correct routing to a sanitary drain.
4. Verify the pump high-level safety switch wiring is intact and connected to the unit’s safety circuit (unit should shut down if the pump fails and reservoir overflows).

Drain Holes & Drain Pans

Drain pans accumulate sludge, algae, and debris that plug the drain outlet even when the main drain line is clear. At each PM:

• Inspect the full drain pan — including under the evaporator coil where the pan is not visible from the access door
• Remove any standing water; flush with a dilute bleach solution
• Clear the drain outlet with a flexible brush or nitrogen purge
• Verify the drain pan slope is correct (minimum 1/8 in. per foot toward the outlet) — a level or reverse-pitched pan traps water even with a clear drain
• Install algaecide tablet where permitted by the authority having jurisdiction
• Check secondary (overflow) drain pan for standing water — presence of water indicates the primary drain is failing

6.5.6 — Preventive Maintenance Checklist Summary

The following table consolidates all key checks from this lesson into a single reference document. Use it as the basis for a site-specific PM form.