Usage:
All Caterpillar Machines With Air Conditioning
Arc suppressors are now being used to reduce the electrical arcing between the contacts of thermostatic switches.
Failures of the 3E-5464, 3E-5465 and 3E-5466 Thermostatic Switches may be caused by arcing due to the inductance of the air conditioner clutch coil. When the thermostatic switch opens, a high voltage can be generated across the switch, causing an electrical arc.
The arc can be reduced by installing an arc suppressor in the compressor clutch coil circuit. The arc suppressor is a diode, connected so that it does not conduct while the compressor is in operation. When the thermostatic switch opens, a voltage of the opposite polarity is generated by the clutch coil. The resulting current will flow through the diode, reducing the intensity of the arc between the switch contacts.
The arc suppressors may be used on machines with 12V or 24V electrical systems.
NOTE: This arc suppression design is not protected against reverse polarity. If the machine's batteries are connected backwards, for example, the arc suppressor may be damaged and/or the system fuse or circuit breaker may open. The arc suppressors can be tested with the 6V-7070 Multimeter or equivalent, on the Diode Test scale. A damaged arc suppressor could test either open or shorted. Always test the arc suppressor when a failed thermostatic switch is replaced, or when the air conditioner fuse or circuit breaker has opened.
The arc suppressor connection varies among different machines. The current compressor models have either Sure Seal® or DT connectors. Some earlier compressors use bullet connectors, but most have a Sure Seal connector at the other end of the harness that connects to the bullet connectors. The arc suppressor can be connected at the Sure Seal or DT connectors, as follows:
Sure Seal Connectors
Illustration 1. Sure Seal Connectors (Contact 1 Positive). (1) Machine harness connector. (2) 105-8827 Arc Suppressor. (3) A/C clutch coil connector.
Illustration 2. Sure Seal Connectors (Contact 2 Positive). (1) Machine harness connector. (3) A/C clutch coil connector. (4) 3E-9169 Arc Suppressor.
1. Determine the polarity of the connector (which contact is powered, and which is grounded). Refer to the machine schematic, or check for the presence of +24V with a 6V-7070 Multimeter or equivalent. Most machines have +24V on contact 1, and ground on contact 2.
2. If contact 1 is the +24V contact: Install a 105-8827 Arc Suppressor (2) between the machine harness connector (1) and the compressor coil connector (3). See Illustration 1.
3. If contact 2 is the +24V contact: Install a 3E-9169 Arc Suppressor (4) between the machine harness connector (1) and the compressor coil connector (3). See Illustration 2.
DT Connectors
Illustration 3. DT Connectors. (1) Machine harness connector. (3) A/C clutch coil connector. (5) 106-8704 Arc Suppressor. (6) 114-2859 Harness.
1. Determine the polarity of the connector (which contact is powered, and which is grounded). Refer to the machine schematic, or check for the presence of +24V with a 6V-7070 Multimeter or equivalent. Most machines have +24V on contact 1, and ground on contact 2.
2. If contact 1 is the +24V contact: Connect a 106-8704 Arc Suppressor (5) to one of the DT plugs on a 114-2859 Harness (6). Connect the other two DT connectors on Harness (6) between the machine harness connector (1) and the compressor coil connector (3). See Illustration 3.
3. If contact 2 is the +24V contact: Modify a 114-2859 Harness (6), by removing both contacts from any one of the DT connectors, and installing them in the opposite positions in the connector. Then connect Harness (6) and the Arc Suppressor as described in Step 2 above.
Coil any excess harness length, and secure with plastic ties as required.
Some production machines are equipped with these arc suppressors. The arc suppressors will be added to other machines at a later time.