This convenient air conditioning start-up checklist has been designed to help maximize reliability, economy, and fuel conservation in the operation of air conditioning equipment.

Information from the files of the Hartford Steam Boiler Inspection and Insurance Co. indicates that a great many failures take place at start-up or early in the cooling season because of inoperative controls or safety devices. Most of these accidents could have been prevented if a little more attention had been paid to readying the equipment for service. It is therefore recommended that the following measures be taken to ensure a trouble-free cooling season and reduce the likelihood of equipment malfunction.

The tips offered here are intended to complement and not replace the recommendations of the equipment manufacturer.


• Energize the crankcase heaters for at least eight hours before start-up and before taking insulation resistance readings of hermetic motor windings. Crankcase heaters should be left energized for the rest of the season so that whenever the compressor is idle, the heater will prevent refrigerant “migration” to the crankcase.

• Test the lubricating oil for color and acidity, and check crankcase oil level.


• Check the air passages of open motors for cleanliness and obstructions.

• Check the condition of and lubricate bearings.

• Take insulation resistance readings. If the readings indicate less than one megohm resistance, don’t start the motor. Check for the cause of the low resistance.


• Inspect starter contacts for deterioration from short cycling, arcing, or corrosion.

• Check terminal connections for tightness.

• Examine the overload protection for defects, and for proper size.

• Check mechanical linkages for binding and excessive looseness.

• Check timing devices for correct operating sequence.


• Determine that the controls are properly calibrated and in working order particularly thermostatic controls, oil pressure safety switches, and flow switches.


• Be sure the circuit is equipped with a moisture indicator and if moisture is indicated, install new liquid line filter-drier cores. Determine and correct the source of the moisture.

• Check the expansion valve for proper operation and superheat settings over the full range of operation.


• Ensure that proper cleaning of heat transfer surfaces for the type of unit in use has been completed prior to operation.

• Cooling towers: Check the baffles for tightness and soundness. Clean the baffles, sump, and the spray nozzles. Check the make-up water valve for proper operation.


• Check the bearings, packings, shaft couplings, and seals. Lubricate bearings.


• Check for broken, cracked, bent, or loose blades. Check hubs, fan shaft, and bearings.

• Check the belt condition and belt tension.

• Replace air filters.


• Check all piping supports for signs of distress.

• Check for external damage and excessive vibration.

Reprinted with permission from the Hartford Steam Boiler Inspection and Insurance Co. technical document #406, "Air Conditioning Start-Up Checklist." The Hartford Steam Boiler Inspection and Insurance Co. provides a range of specialty insurance coverages for business, home, and farm. One of the world’s leading equipment breakdown insurers, HSB helps clients reduce risk through a combination of specialty coverages, engineering-based risk management strategies, and loss reduction services. For more information, visit

Publication date:04/09/2007