Every new and remanufactured Horton DieslTemp air operated fan clutch produced after April 7, 1995 is equipped with the patented System Sentry. The System Sentry is located in one of the raised nodes on the top surface of the Piston Friction Disc (Pfd). The systems Sentry is designed to act as a thermal fuse, allowing the fan clutch to disengage if it encounters excessive heat build up.
If a fan clutch PFD slips, friction is caused which quickly leads to excessive heat. This heat will eventually damage the fan clutch, shortening its expected life. If exposed to this heat the System Sentry responds by disengaging the fan clutch before serious damage can occur.
This disengagement is possible because an additional air outlet has been created between the air chamber and the System Sentry. During normal operation this air passage remains closed.
In the event of fan clutch slippage, heat builds at the outer edge of the PFD. This heat works its way toward the center of the fan clutch. When sufficient levels of heat reach the System Sentry the center of the plug melts. This allows air pressure in the fan clutch to drop, disengaging the fan clutch immediately. This air leak will not significantly impact the rest of the vehicle air system.
Troubleshooting the fan clutch and controls should be done promptly to locate the problem, which caused the System Sentry release of the fan clutch. First locate and remove anything that may be an obstruction to the fan blade. Temporarily plug the System Sentry opening and check the fan clutch for leaks. If no leaks are found, check the solenoid and controls accordingly.
It is absolutely essential to eliminate any problem found during troubleshooting before making repairs to the System Sentry fuse. A replacement System Sentry fuse is part of Horton's Minor Repair Seal kit. Horton recommends installing the entire seal kit after any System Sentry release.
In the event of a System Sentry release the fan clutch can be locked up mechanically by installing two 5/16 NC by 1" long bolts through the PFD into the threaded holes of the plate behind it. This is at temporary fix until proper service work can be performed.
*Please note during repair that the System Sentry plug is left hand-threaded. Also note that the installation of a seal kit due to System Sentry release of a fan clutch is not a warrantable repair.