Okay, that's a dangerous situation, and you're right to be troubleshooting it carefully. The fact that you have high voltage on the ground rod, especially related to the AC unit's operation, points strongly to a ground fault within the unit itself. Here's a breakdown of how I would approach this

Immediate Safety Considerations
Turn off the AC unit at the breaker. Keep it off until you find and fix the fault. This is paramount. Ensure the area around the AC unit is clear of people and pets. Post a warning sign if necessary. Double-check your own grounding practices

Make sure you are using appropriate PPE for working with electricity.

Troubleshooting Steps1. Confirm Isolation



With the AC unit breaker off

Measure the voltage between the ground rod and the neutral/ground at your main electrical panel. It should be very close to zero volts. This confirms that the voltage is indeed coming from the AC unit and not some other external source.

Measure Resistance to Ground

With the breaker OFF, use a multimeter to measure the resistance between each of the AC unit's conductors (both L1 and L2) and the unit's chassis/ground.

This is a crucial step. A low resistance reading (anything significantly less than infinity) indicates a ground fault. Ideally, you should see very high resistance (megaohms or higher) between the conductors and ground.2. Inspect the AC Unit Wiring and Components



Visually Inspect Everything

Carefully examine all wiring within the AC unit. Look for: Burn marks Melted insulation Wires that are touching metal parts of the chassis Signs of rodent damage.

Check the Blower Motor

Since it was recently installed, double-check: That it's wired correctly. That its ground wire is securely connected to the chassis. Measure the resistance from the blower motor wires to the motor body. You shouldn't have a low resistance to ground.

Check Capacitors

AC units often use capacitors for starting and running motors. Look for bulging, leaking, or physical damage. Although a bad capacitor isn't usually a ground fault source, a shorted capacitor could contribute to the problem by stressing other components.3.

Compressor Testing (Most Likely Culprit)



Disconnect the Compressor

Carefully disconnect the wires leading to the compressor. Label them clearly!



Resistance to Ground Test

Use your multimeter to measure the resistance between each of the compressor terminals (where you disconnected the wires) and the compressor's metal casing.

You are looking for a low resistance reading. Any low reading indicates a faulty compressor.

Winding Resistance Test (Less Critical, but Helpful)

Measure the resistance between the compressor terminals themselves. This confirms the windings are not open. Compare the values to the compressor's specifications (if available). Grossly different values can suggest internal winding issues.4.

Isolate and Replace



If the Compressor is Faulty

If you find a low resistance to ground on the compressor, it almost certainly has an internal short and needs to be replaced. This is the most likely scenario.

If No Compressor Fault Found

If the compressor tests okay (unlikely, given your symptoms), continue tracing the wiring and components. The short could be in a contactor, relay, or other device within the AC unit.

Important Considerations



"Voltage Creeping Down"

The fact that the voltage "creeps down" after the rotor breaks suggests that the fault is related to the magnetic field within the compressor motor. It could be that the initial surge of current when the compressor tries to start is causing a breakdown in insulation. After a rotor break, you're left with a partially broken circuit and the voltage is dropping as current slowly finds its way to ground.

No Neutral

The fact that there's no neutral wire running to the unit doesn't change the fact that you have a ground fault.

Final ThoughtsHigh voltage on the ground rod is a severe safety hazard. Do not operate the AC unit until you've located and repaired the fault. If you are not comfortable working with electricity, call a qualified HVAC technician or electrician. They have the experience and tools to diagnose and fix the problem safely. Replacing a compressor is a specialized job that often requires specific tools and knowledge of refrigerants.

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