While you can *temporarily* power the clutch directly from the battery (potentially damaging the compressor if done incorrectly), this bypasses the crucial safety and control mechanisms. The fact that it only works with "running power" means the problem lies within the normal operating circuit, not just a blown fuse or relay.
Here's why a simple jump won't fix the underlying issue:
* Compressor Clutch Relay: There's almost certainly a relay that controls power to the compressor clutch. This relay is activated by the AC system's control circuit, not just a simple switch. The relay itself might be faulty, or there's a problem with the signal *to* the relay.
* Pressure Switch: The AC system has a pressure switch that prevents the compressor from running if the refrigerant pressure is too low (to protect the compressor). A faulty pressure switch could prevent the relay from engaging.
* Cycling Switch: A cycling switch might also be involved, preventing the compressor from running continuously.
* Temperature Sensor: The system may use a temperature sensor to control compressor operation.
* Wiring Issues: There could be a break or short in the wiring between the relay, pressure switch, and compressor.
* AC Control Module (or similar): The AC system's control module (or a similar component) may be malfunctioning, preventing it from sending the signal to engage the compressor clutch.
In short: You need to diagnose the problem systematically. Jumping the clutch directly is a dangerous workaround and doesn't address the root cause. You'll need to:
1. Check the relay: Test the relay for continuity and proper operation. Replace if necessary.
2. Check the pressure switch: Ensure it's functioning correctly and is making contact.
3. Inspect wiring: Look for broken, damaged, or corroded wiring between the compressor, relay, and control components.
4. Check fuses (though less likely to be the problem given your description): There are probably fuses involved in the AC circuit somewhere.
5. Consult a wiring diagram: A wiring diagram specific to your 1996 Isuzu model will show the complete AC circuit and help you trace the problem.
Jumping the clutch repeatedly can damage the compressor, so avoid doing this unless it's absolutely necessary for testing a specific component. It's best to find and fix the actual problem rather than resorting to dangerous workarounds. A qualified mechanic can properly diagnose and repair the AC system.
