RACA Journal March 2026 RACA_Mar_2026 | Page 38

SOLUTIONS voices

Example of a serpentine belt configuration. The vanes are sealed against the rotor housing by centrifugal force and lubricating oil. The oil sump and oil pump are located on the discharge side, so that the high pressure forces oil through the oil pump, and then onto the base of the vanes keeping them sealed against the rotor housing. During idle, an occasional vane noise from the compressor may be heard. This is due to the time taken for lubricating oil to circulate through the system.

Example of a serpentine belt configuration.

Stewart, the compressors mounting often consists of a bracket to mount the compressor to the engine, a belt idler pulley, compressor drive belt and possibly an extra drive pulley for the crankshaft.

The compressor mounting is often manufactured of either plate, cast iron, steel or aluminium; this bracket should exhibit excellent noise absorption qualities especially if using a piston type compressor.

Moving on to the idler pulley, we find a small pulley normally used in conjunction with a belt adjusting mechanism, also used when a belt has a long distance between pulleys to absorb belt vibrations.

Some vehicles do not have an extra pulley to accommodate an A / C drive belt, in which case an extra pulley is bolted onto the existing crankshaft pulley. The most common belt used is the serpentine belt, although V belts are also used.

Stewart, power is transferred from the vehicle primary driver to the air-conditioning compressor via the belts to the drive pulley and compressor clutch mechanism. Some vehicles do not have a clutch fitted, typically on variable capacity compressors.

The clutch is designed to connect the rotor pulley to the compressor input shaft when the field coil is energised. The clutch is used to transmit the power from the engine crankshaft to the compressor by means of a drive belt.

When the clutch is not engaged the compressor shaft does not rotate and refrigerant does not circulate as the rotor pulley free wheels. The field coil is actually an electromagnet – once energized, it draws the pressure plate towards it, locking the rotor pulley and the pressure plate together causing the compressor internals to turn, creating pressure and circulating refrigerant.

Stewart, I hope that this helps with your understanding of the types and basics of operation of an automotive air-conditioning system compressor. RACA

Expanded clutch pack / pulley.