Capacitor failure is the single most common air conditioning repair technicians handle. But it is not the only repair that comes up repeatedly every cooling season. Certain components fail more often than others due to heat exposure, electrical stress, and lack of maintenance.
Here is a breakdown of the most frequent AC repairs, what causes each one, and what the fix involves.
Capacitor Failure
A capacitor stores and releases electrical energy to start and run the compressor and fan motors. It handles high voltage repeatedly every time the system cycles on. Heat accelerates capacitor degradation, which is why failures spike during summer when outdoor temperatures push the component beyond its rated operating range.
A failing capacitor produces recognizable symptoms:
- The outdoor fan spins slowly or not at all
- The system hums at startup but the compressor does not engage
- The AC shuts off shortly after starting
- Indoor temperature rises despite the system appearing to run
Capacitors are rated in microfarads. A capacitor reading below 90 percent of its rated value on a capacitance meter is considered weak and should be replaced before it fails completely. Replacement is straightforward and restores full motor function immediately.
Refrigerant Leaks
Refrigerant leaks are the second most common air conditioning repair call. A leak develops at brazed joints, Schrader valve cores, or along the refrigerant line where vibration causes metal fatigue over time. Systems do not consume refrigerants. Any measurable drop in charge level confirms a leak exists somewhere in the circuit.
A technician locates the leak using:
- Electronic leak detector sensitive to refrigerant vapor
- UV dye injected into the system and inspected with a UV light
- Nitrogen pressure test to identify the leak point by pressure drop
EPA Section 608 regulations require that refrigerant leaks above a threshold rate in commercial systems be repaired within 30 days. For residential systems, the same standard applies as best practice. Recharging without repairing the leak returns the system to the same failure point within one to two seasons.
Contactor Failure
The contactor is an electrically operated switch that connects line voltage to the compressor and outdoor fan motor when the thermostat calls for cooling. It opens and closes hundreds of times per season. The contact points pit and burn over time from electrical arcing, eventually failing to close completely or welding shut in the closed position.
Signs of contactor failure include:
- The outdoor unit does not start despite the thermostat calling for cooling
- The system runs continuously without cycling off
- A chattering or buzzing sound from the outdoor unit
- Visible burn marks or pitting on the contact points
A failed contactor that stays open stops cooling entirely. One that welds shut runs the compressor continuously, which overheats and damages it. Contactor replacement during a maintenance visit costs significantly less than compressor replacement caused by a welded contactor left unaddressed.
Clogged Condensate Drain Line
The evaporator coil removes humidity from indoor air as it cools. That moisture collects in a drain pan and exits through a condensate drain line. Algae, mold, and debris accumulate inside the line over a cooling season, eventually blocking it completely. A blocked drain causes the pan to overflow, triggering a float switch that shuts the system down to prevent water damage.
Clearing the drain line involves:
- Flushing with a wet/dry vacuum at the outdoor drain exit point
- Pouring a diluted bleach solution into the access port near the air handler
- Checking the float switch for correct operation after clearing
A clogged condensate line is one of the most preventable air conditioning repair calls. Flushing the line at the start of each cooling season eliminates most blockages before they develop. Some systems include a secondary drain pan with a separate overflow switch as a backup.
Dirty Evaporator and Condenser Coils
Coil fouling reduces heat transfer efficiency across both the indoor evaporator and outdoor condenser. A dirty evaporator coil insulates itself from the airstream, reducing its ability to absorb heat. A dirty condenser coil traps heat inside the outdoor unit, raising head pressure and stressing the compressor.
The U.S. The Department of Energy states that dirt accumulation on evaporator coils reduces heat-absorbing capacity and increases energy use, making coil cleaning a core part of annual maintenance. Coil cleaning during an annual tune-up at Redeemed Heating, Cooling, Duct Cleaning & Plumbing restores rated heat transfer capacity and reduces the electrical load on the compressor. Systems with clean coils run shorter cycles and consume less energy per hour of operation than systems with fouled coils running extended cycles to compensate.
Blower Motor Problems
The blower motor drives the indoor fan that circulates air across the evaporator coil and through the ductwork. Motors fail from bearing wear, capacitor degradation, or overheating caused by restricted airflow from a clogged filter. A failing blower motor reduces airflow below the system’s design specification, which causes the evaporator coil to freeze and cooling output to drop.
Blower motor failure shows up as:
- Weak or uneven airflow at supply registers
- A squealing or grinding sound from the air handler
- The system running but no air movement at the vents
- The blower starting slowly or failing to reach full speed
Variable-speed blower motors are more energy efficient than single-speed units but have more complex control boards that can also fail. A technician checks motor amperage draw against nameplate ratings to confirm whether the motor or its capacitor is the failing component.
Faulty Metering Device
The metering device controls refrigerant flow into the evaporator coil. The two most common types are the thermostatic expansion valve and the fixed orifice. A stuck or failed metering device sends either too much or too little refrigerant into the coil. Too much causes liquid refrigerant to reach the compressor, which damages it. Too little starves the coil and reduces cooling capacity significantly.
Diagnosing a metering device problem requires measuring superheat and subcooling values at the system. Superheat measures how much the refrigerant has absorbed above its boiling point at the evaporator outlet. Subcooling measures heat removed from liquid refrigerant at the condenser outlet. Both readings outside the manufacturer’s specified range point to a metering device issue rather than a refrigerant charge problem.
What Prevents These Repairs
Most of the repairs above share a common factor: they are detectable before failure during a routine maintenance visit. Annual tune-ups catch weak capacitors, pitted contactors, low refrigerant charge, fouled coils, and blocked drain lines before any of them cause a breakdown.
Preventive steps that reduce repair frequency include:
- Replacing the air filter every 30 to 90 days
- Scheduling an annual tune-up before the cooling season starts
- Keeping the condenser unit clear of debris year-round
- Flushing the condensate drain line each spring
At Redeemed HVAC, maintenance plans cover the full diagnostic sequence each season, including capacitor testing, refrigerant charge verification, coil cleaning, and drain line flushing. Call 417-241-5687 to schedule before the next cooling season starts.