Carrier Air Conditioner Error Code 4

Error code 4 on a Carrier air conditioner means the CADM (Compressor and Air Handler Diagnostic Module) has detected a Locked Rotor condition. This means the compressor motor attempted to start but could not get the rotor spinning, drawing excessive current in the process. The fault is triggered to protect the system from motor burnout. The most common causes are low supply voltage, liquid refrigerant flooding the compressor, or mechanically seized compressor bearings.

No, you should not continue attempting to run the system with a Locked Rotor fault active. Each failed start attempt drives extremely high current through the compressor motor windings, which can cause permanent motor burnout or damage to the CADM module. Shut the system off at the thermostat and disconnect power until the root cause has been diagnosed and corrected.

Resetting the unit by cycling power may temporarily clear the fault code, but if the underlying cause has not been resolved, the CADM will detect the locked rotor condition again on the next start attempt and repost the fault. Repeated reset attempts without fixing the root cause risk permanent compressor damage. A proper diagnosis must be completed before the system is returned to service.

Most of the diagnostic and repair work for a locked rotor condition requires professional tools and EPA certification. Checking your home's supply voltage at the panel and ensuring the disconnect is fully seated are steps a homeowner can safely take. However, testing refrigerant charge, inspecting the compressor mechanically, and replacing components like capacitors or the compressor itself should be handled by a licensed HVAC technician.

Repair costs vary widely depending on the root cause. If the issue is a failed capacitor, costs are typically in the range of $100 to $300 including labor. A refrigerant flush and system recharge can range from $200 to $600. If the compressor itself is seized and requires replacement, costs can range from $1,200 to $2,800 or more depending on unit size and local labor rates.