AC Compressor Amp Draw Explained: What High or Low Amps Mean
Compressor amp draw is one of the most valuable diagnostic measurements in HVAC service. It must always be interpreted together with voltage, refrigerant pressures, superheat, subcooling, airflow, and compressor temperature.
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RLA: Expected running current under normal operating conditions.
LRA: Brief inrush current when the compressor starts.
Comparing measured current to the nameplate helps identify abnormal loading.
Common Causes of High Amp Draw
Dirty condenser coil
Failed condenser fan
High head pressure
Refrigerant overcharge
Low supply voltage
Weak run capacitor
Short cycling
Internal mechanical wear
Locked rotor
Extreme outdoor temperatures
Common Causes of Low Amp Draw
Low refrigerant charge
Weak compressor pumping
Internal valve leakage
Low cooling load
Low suction pressure
Open winding
Control or staging problems
Recommended Diagnostic Workflow
Verify line voltage.
Test the run capacitor.
Inspect the contactor and voltage drop.
Measure startup and running amps.
Record suction and head pressures.
Calculate superheat and subcooling.
Measure compressor shell temperature.
Compare all readings before making a repair decision.
Comparison Guide
Condition
Likely Pattern
High amps + high head pressure
Dirty condenser, overcharge, airflow restriction
High amps + low voltage
Electrical supply problem
Low amps + weak cooling
Low refrigerant or weak compressor
High startup amps
Locked rotor, weak capacitor, high load
Typical Homeowner Symptoms
Breaker trips
Outdoor unit noisy
Compressor overheats
AC runs continuously
Weak cooling
Compressor hums but struggles to start
Repair vs. Replace
High or low amp draw does not automatically mean the compressor has failed. Correcting condenser airflow, replacing a capacitor, repairing electrical issues, or correcting refrigerant charge may restore normal operation. Compressor replacement is considered when testing confirms internal electrical or mechanical failure.
