Air Conditioner Power Supply Repair – How We Do It
Service Overview
- Average Cost: KES 2,500 – 10,000 depending on issue complexity
- Service Duration: 1-3 hours for most repairs
- Common Problems: Tripped breakers, blown fuses, damaged disconnects, contactor failures
- Safety Priority: All work performed with proper lockout/tagout procedures
- Emergency Service: Available for complete power failures
- Success Rate: 95% of power issues resolved same visit
When your air conditioner won’t turn on or randomly shuts off, power supply problems are often the culprit. These issues range from simple tripped breakers to complex electrical faults requiring systematic diagnosis and repair. Our power supply repair service quickly identifies and resolves electrical issues that prevent your AC from receiving the reliable electricity it needs to operate.
Power Supply Diagnostic Process
Our diagnostic process begins at the main electrical panel, where we verify the air conditioner circuit breaker sits firmly in the ON position and shows no signs of damage or overheating. We test voltage at the breaker terminals using proper safety procedures, confirming that power is available at this point in the circuit. A tripped breaker gets reset only after we determine why it tripped—simply resetting without identifying the cause often leads to immediate re-tripping or worse, allows a developing problem to escalate.
From the main panel, we trace the power path to the disconnect switch near the outdoor unit. Using a non-contact voltage tester and then a multimeter, we verify voltage presence at each connection point. This systematic approach pinpoints exactly where power loss occurs. Complete absence of voltage at the disconnect but presence at the panel indicates a wiring problem between these points. Voltage at the disconnect but not at the unit points to issues in the final connection segment.
We test both legs of the power supply (240V systems use two hot legs), as losing one leg causes unique failure patterns. With only one leg energized, compressors may hum but fail to start, while control circuits might remain powered. This single-leg failure commonly results from loose wire connections, failed breaker poles, or problems at the utility transformer.
Breaker and Panel Issues
Circuit breakers fail in multiple ways beyond simple tripping. Internal contacts degrade from arcing during normal switching or from sustained operation near the breaker’s current rating. We test breaker operation by deliberately tripping it using the test button, then resetting and observing that it firmly clicks into position. Loose or spongy breaker action indicates internal damage requiring replacement.
When breakers trip repeatedly, we must determine whether they’re responding to legitimate overload conditions or failing unnecessarily. Using a clamp meter, we measure actual current draw during startup and steady operation, comparing measurements to the breaker’s rating and the air conditioner’s specifications. Current exceeding the breaker rating indicates either a problem with the AC unit drawing excessive current or an undersized breaker for the application.
Arc fault and ground fault circuit breakers sometimes trip from electrical noise or minor ground leakage that wouldn’t damage equipment but exceeds the breaker’s sensitivity threshold. In these cases, we verify the trip isn’t indicating legitimate faults, then consider whether standard thermal-magnetic breakers are appropriate for the application, coordinating any changes with licensed electricians to maintain code compliance.
Disconnect Switch Repairs
The disconnect switch near the outdoor unit is a critical safety device and common failure point. We remove the cover and inspect the interior for signs of overheating, burned connections, or corrosion. Disconnect switches exposed to weather deteriorate from moisture infiltration, with rust and corrosion increasing connection resistance and eventually causing failure.
For fused disconnects, we remove and test each fuse using a multimeter’s continuity function. Blown fuses must be replaced with identical type and rating—never use fuses with higher ratings than specified as this defeats overcurrent protection. We inspect fuse clips for corrosion and proper tension, as loose fuse holders create resistance that generates heat and causes premature fuse failure.
Non-fused disconnects use a switch blade mechanism that sometimes fails to make solid contact. We inspect contact surfaces for pitting or carbon buildup, cleaning them with approved contact cleaner and fine abrasive when needed. Severely deteriorated contacts require complete disconnect replacement. We also verify the disconnect mechanism positively locks in both ON and OFF positions, as switches that can’t reliably open create safety hazards during maintenance.
Contactor Replacement and Repair
The contactor inside the outdoor unit serves as the main power switch controlled by the thermostat. This electromagnetically operated switch clicks audibly when engaging—homeowners often report hearing the click but having no compressor operation, indicating the contactor closed but power isn’t reaching the compressor. We inspect contactor contacts for pitting, burning, or welding that prevents proper operation.
Minor pitting can be dressed with a contact file, restoring smooth contact surfaces. However, severely damaged contactors require replacement as filed contacts may not last long. We verify the contactor’s coil operates at the correct voltage and draws appropriate current. A weak coil may not pull the contacts closed firmly enough to handle full load current, causing arcing and rapid contact deterioration.
After installing a replacement contactor, we select one with appropriate voltage rating (matching the coil voltage supplied by the control transformer) and current rating (exceeding the compressor’s locked rotor amperage). Undersized contactors fail quickly under the stress of compressor starting current. We also verify the contactor includes proper arc suppression circuits that extend contact life.
Transformer and Control Circuit Issues
The control transformer steps high voltage (typically 240V) down to low voltage (usually 24V) for thermostat operation and control circuits. Transformer failure prevents the entire control system from functioning even when main power is available. We test transformer output voltage, expecting to see 24-28V AC at the secondary terminals. Absence of secondary voltage with primary voltage present indicates transformer failure.
We check for short circuits in the control wiring that overload the transformer. Crimped wires, incorrect thermostat wiring, or failed control components can draw excessive current that blows the transformer’s internal fuse or burns out the secondary winding. Before replacing a failed transformer, we must identify and correct whatever caused the failure to prevent immediate repeat failure.
Control circuit repairs include replacing damaged wiring, repairing loose connections at control board terminals, and ensuring proper wire routing that protects low-voltage conductors from heat and physical damage. We trace control circuits from the thermostat through the transformer to the control board and contactors, verifying continuity and proper voltage at each point.
Capacitor and Startup Circuit Repairs
While not strictly power supply issues, failed capacitors prevent the compressor from starting despite adequate power supply. This confuses homeowners who hear the contactor close and assume power is reaching the compressor. We test both start and run capacitors, measuring their actual capacitance and comparing it to rated values. Capacitors showing more than 10% deviation from rating require replacement.
We also inspect the potential relay on systems equipped with start capacitors, verifying proper operation that connects the start capacitor during startup then disconnects it once the compressor reaches running speed. Failed relays leave start capacitors in the circuit continuously, causing overheating and premature failure, or fail to connect them at all, preventing compressor startup.
Verification and Testing
After completing repairs, we energize the circuit and measure voltage at all critical points with the system at rest. We then initiate a cooling cycle, observing startup behavior and measuring voltage under load. We verify voltage drop during startup remains within acceptable limits and that the compressor transitions smoothly to running operation. We cycle the system multiple times, ensuring reliable startup and no intermittent failures that might indicate marginal repairs requiring additional attention.
