The following are the most frequent symptoms and causes of clutch related problems.
Burnt Hub, Pulley, and/or Coil
Inadequate voltage to the coil will result in overheating of the internal winding and cause the clutch hub to slip against the face of the pulley. A compressor in the stages of failing due to slugging or loss of lubrication, or operating under a high pressure condition will cause the clutch to slip. The slipping occurs continuously during compressor operation and can subject both the clutch and coil to extreme temperatures up to 1,200 degrees Fahrenheit. This will quickly destroy the clutch and its internal components and is a type of failure that is not warranted.
Bearing failures are usually caused by system problems. Very seldom is a bearing itself the culprit of a failed or locked up compressor. For example, if the clutch slips severely due to a high pressure or low voltage condition, or due to compressor slugging, the excessive heat generated by the slipping will quickly melt and destroy the bearing seal. The bearing then loses its grease and locks up or falls apart, usually destroying the clutch in the process. This type of bearing failure is not covered under warranty, since the bearing was not the root cause of the problem. Warranty may be considered only if the bearing is intact, and there is no evidence of excessive heat, a compressor or a/c system problem, or signs of installation related problems. Manufacturing defects in clutch bearings are rare, and warranty allowances are usually associated with excessive noise symptoms only (see following condition).
If the complaint is noise related only, a defective clutch pulley bearing could be the source of the problem. Check for a rough or poorly operating bearing by holding the clutch armature hub stationary, and rotating just the pulley. If excessive noise or difficulty in ease of rotation is observed, the bearing may be suspect. However, as with the failed bearing situation described above, several factors can cause the bearing to become noisy or rough in operation. A rough bearing can also be in the early stages of failing due to system problems involving extreme heat, which is often the case if the compressor clutch has been operating sufficiently for some time and then becomes noisy. Most factory bearing defects become evident in the first hours of compressor operation. Warranty consideration for failed compressors and clutches described as noisy will be provided only if there are no obvious signs that the failure was caused by other factors.
Burnishing is the cycling of the clutch to allow a wearing in of the engagement surface area. The reason for burnishing a clutch is to increase the initial starting torque. Most technicians fail to follow this important procedure when replacing a compressor or clutch. An unburnished clutch can produce a low torque condition, causing the clutch to slip and thereby fail.
Improper Rotor to Hub Air Gap
An incorrect air gap can cause a clutch to engage or disengage improperly. This is particularly true on Sanden, Seltec, and Frigidaire/GMC style compressor clutches. Before operating a compressor of this type, check the hub/armature to rotor/pulley air gap. Check the required specifications for your particular type of compressor clutch in the illustrated section of the A/C parts catalog. These clutches may involve adding or removing shims to properly gap the hub. New manufactured compressor and clutch assemblies are properly gapped at the factory. Most clutch failures or problems relating to improper air gap can be traced to improper clutch replacement in the field. Check to see if this applies before returning possible warranties.
Misaligned Belt or Use of Wrong Clutch
In some cases clutch failure can be contributed to a slipping, under or over tensioned, or misaligned pulley belt. Further checking may discover that the wrong clutch (with improper mounting distance specifications) was installed onto the compressor. A clutch with as little as 1/8″ offset in alignment can cause problems. Sometimes a misalignment condition can be traced to a cracked or loose compressor mount bracket on the engine. Look for excessive wear and/or indications of rubbing on the inside of the pulley groove before returning possible warranties.
Open Circuit inside Field Coil
This type of condition is rare, and can only be verified by removing the clutch pulley and hub from the compressor. The field coil core is held in place by an outer epoxy resin. If the bond between the epoxy and the winding fails, the coil may be subject to move, which could lead to a break in the coil wire, producing an inoperative clutch. With the exception of a fine crack around the outer diameter of the epoxy, there is no outward indication of a problem. However, the open circuit can be found with a resistance (ohm) meter. If an open circuit is found, with no evidence of melted resin or installation damage, the coil itself may be warranted.
Failed Field Coil Mounting Flange Welds
This condition is specific only to CCI/York/Tecumseh style clutches. The field coil assembly consists of a magnetic field core that encloses the coil, and a flange which mounts onto the compressor. The field core and flange are assembled at the factory, joined together by spot welds. Although it seldom occurs, a faulty spot weld will cause rubbing between the outside of the field core and inside of the pulley, eventually causing an open circuit and inoperative clutch. Be aware that in most cases involving failed welds and broken coil flanges, a severe vibration problem usually exists. This is especially true on Detroit Series 60 engines. In some cases the vibration is so extreme that the screws holding the coil onto the compressor will vibrate loose, causing the clutch assembly to become unattached from the compressor shaft. Without a secure mount, the clutch and coil will literally be torn apart by the force of the drive train belt attempting to turn the clutch pulley. The compressor shaft is usually also destroyed in the process. An occurrence of this nature voids all warranty on both the compressor and clutch.
Faulty Lead Wire
If the lead wire connected to the field coil is faulty, the clutch becomes inoperative. This will be evident at the time of installation, and seldom occurs afterwards. However, evidence of obviously damaged or cut lead wires is not a cause for warranty consideration.