CRAC/CRAH Unit Operation & Operator-Level Maintenance

What CRAC and CRAH Units Do

A Computer Room Air Conditioner (CRAC) unit uses a refrigeration cycle — compressor, condenser, expansion valve, and evaporator coil — to cool and dehumidify air inside a data center. A Computer Room Air Handler (CRAH) unit uses chilled water supplied from a central plant instead of its own refrigerant circuit; a cooling coil inside the unit transfers heat from the room air to the chilled water loop. Both types circulate air through a filter, across a coil, and back into the room using one or more blower fans. As a data center technician, you will encounter both types. This lesson focuses on operator-level maintenance — tasks you are authorized to perform without a licensed HVAC mechanic — primarily on CRAC units.

Why Operator-Level Maintenance Matters

Dust-clogged filters force blowers to work harder, reduce airflow, and raise supply air temperatures. A fouled coil face insulates the coil and reduces heat transfer. Standing water or biological growth in a drain pan can block condensate drainage, leading to water damage or humidity spikes. Neglecting these items degrades cooling capacity and can trigger thermal shutdowns of IT equipment. Regular inspection and filter replacement are the first line of defense against these failures.

Lockout/Tagout Before You Open the Unit

A CRAC unit contains high-voltage electrical components (blower motors, control boards, and on some units, electric reheat elements), moving fan blades, and refrigerant under pressure. You must complete lockout/tagout (LOTO) before opening any panel that exposes electrical parts or rotating machinery. This is an OSHA requirement under the Control of Hazardous Energy standard. Skipping or shortcutting LOTO is a critical error — in this course it triggers an immediate retest, and on the job it can be fatal.

The LOTO sequence for a CRAC unit follows six steps:

1. Notify all affected personnel that the unit will be shut down.

2. Identify every energy source: the main electrical disconnect (and any secondary circuit breakers), and note that refrigerant pressure exists in the piping even after power is off.

3. De-energize the unit using its normal shutdown procedure on the digital controller, then open (turn off) the main disconnect or circuit breaker.

4. Isolate the energy source — place your personal padlock and hasp on the disconnected breaker or disconnect handle so it cannot be re-energized.

5. Tag the lockout point with a standardized danger tag listing your name and the date.

6. Verify zero-energy state — attempt to restart the unit using the controller and confirm it does not start; use a non-contact voltage tester on the terminals inside the electrical compartment to confirm no voltage is present.

Only after verification may you open access panels to the filter compartment, drain pan, or coil.

PPE for This Task

Wear safety glasses whenever you are inside the unit — loose debris can fall from filters or coil fins. Wear gloves rated for the cleaning chemicals you use in the drain pan, and to protect against sharp coil fins. If the manufacturer's manual specifies additional PPE, follow it.

Inspection Procedure

Air filter: Slide the filter out according to the manufacturer's guide. Hold it up to a light source. A filter that blocks significant light, shows visible gray or brown loading, or has reached its scheduled replacement interval should be replaced. Note the filter's dimensions and MERV rating printed on the frame, and install only the manufacturer-specified replacement media. Insert the new filter with the airflow arrow pointing in the direction of airflow (toward the coil, not toward the return-air opening). Log the old filter condition and the new filter's part number on your maintenance form.

Drain pan: Inspect for standing water, algae, or debris. The pan should be clean and the drain port unobstructed. Use the manufacturer-approved cleaning solution to wipe the pan. Do not pour cleaning chemicals directly into the refrigerant or chilled-water piping.

Coil face: Look across the coil fins with a flashlight. Fins should be straight and free of heavy dust accumulation. Operator-level maintenance does not include chemical coil cleaning or fin straightening — those are escalated to a qualified HVAC technician. Document anything unusual.

Restarting the Unit and Reading the Digital Controller

After closing all panels and removing your lock and tag, restart the unit per the manufacturer's startup procedure — typically engaging the main disconnect, then pressing the ON button or navigating the controller menu. Observe the digital controller display for:

• Supply air temperature (SAT): the temperature of air leaving the unit toward the IT equipment.
• Return air temperature (RAT): the temperature of warm air entering the unit from the room.
• Humidity setpoint: the target relative humidity the unit maintains.

Allow the unit to stabilize (typically several minutes) before adjusting setpoints. To practice setpoint adjustment, navigate to the temperature setpoint in the controller menu and raise it by 1 °C, then watch the SAT trend on the display. Return it to the original value, then lower it by 1 °C and observe again. Log each adjustment, the time, and the unit's response (did compressor staging change? did fan speed change?). Always return setpoints to their original values unless a supervisor directs otherwise.

Maintenance Documentation

Every inspection and maintenance action must be recorded on the site maintenance log: date, unit ID, technician name, filter condition and part number installed, drain pan condition, coil face condition, and any abnormalities noted. Good records support warranty claims, predictive maintenance scheduling, and regulatory compliance.