Ag Power Web Enhanced Course Materials

If you experience any problems with the site, please contact Pete Hoffman immediately so corrections can be made. Pete can be reached on campus, via email at phoffman@swtc.edu or by phone at 1.800.362.3322 ext 2727.

Magnetic Clutch

The clutches on machine air conditioning systems are of two types:

• Rotating coil
• Stationary coil

Rotating Coil

• Clutches have the magnetic coil inside the pulley and rotating with it. The electric current is carried to the coil by brushes mounted on the compressor frame and contacting a slip ring mounted on the inside of the rotating pulley.

Stationary Coil

• Clutches have the magnetic coil mounted on the frame of the compressor and it does not rotate. Since the coil is stationary, correct spacing is important to prevent the rotating pulley from contacting the coil, while still bringing the hub and armature into position for the fullest attraction of the magnetic force.

• When replacing either the clutch unit or the coil must note carefully that the voltage of the replacement unit is correct for the vehicle on which it is to be installed.

• All clutches operate on the same principle whether the magnetic coil rotates or is stationary. Each has a wound core located within a metal cup acting like a horseshoe magnet when the coil is energized electrically (Fig. 35).

• The pulley rotates on a bearing mounted on the clutch hub (Fig. 34) except the Frigidaire com­pressor, which mounts the bearing on the com­pressor front head assembly. The pulley is free to rotate without turning the compressor crankshaft any time the clutch coil is not energized. The free-rotating pulley and non-energized clutch coil stop compressor operation.

• An armature plate is mounted by a hub to the compressor crankshaft and is keyed into place and locked securely with a lock nut, thus making connection to the crankshaft.

• Energizing the clutch coil creates lines of magnetic force from the poles of the electromagnet through the armature, drawing it towards the shoe plate or rotor that is a part of the pulley assembly (Fig. 35). The solid mounting of the pulley prevents the pulley from moving in a lateral direction; however, the armature can move until it contacts the rotor. Magnetic force locks the rotor and the armature plate together. This solid connection then allows the pulley to rotate the compressor crank­shaft and operate the compressor. Compressor operation will continue until the electrical circuit is broken to the clutch coil, when the magnetic force is de-energized. The rotor and armature then separate, and the pulley rotates freely without rotating the compressor crankshaft.

• Slots are machined into both the armature and the rotor to concentrate the magnetic field and increase the attraction between the two when energized. Some scoring and wear is permissible between these plates. However, it is important that full voltage be available to the clutch coil as low voltage will prevent a full build-up of magnetic flux to the plates.

• The correct spacing between the pulley and the coil on stationary coil models must be maintained to prevent the pulley from dragging against the coil. Correct spacing must also be maintained between the rotor and the armature.

• Too close a clearance will allow the two plates to contact each other in the "OFF" position, while too wide a space can prevent the rotor from con­tacting the armature solidly in the "ON" position. Any of these variations can cause a serious clutch failure.

• Also be sure that the mating surfaces are not warped (from overheating)

Part Identification - Magnetic Clutch