8 Common AC Repair Problems and How to Fix Them

Wisconsin summers hit hard. When your AC starts struggling during a humid July in Wauwatosa or Mequon, knowing what's wrong—and what to do next—saves time and money. Air conditioners work overtime in the Greater Milwaukee area, where summer humidity climbs alongside the temperature. Breakdowns happen. The good news is that most failures trace back to a handful of recurring problems, and understanding them helps you decide whether to grab a screwdriver or pick up the phone.

Here are eight of the most common AC repair issues, along with practical guidance on what you can handle yourself and when it's time to call Burkhardt Heating, Cooling, Plumbing & Electric at (414) 355-5520.

1. Low Refrigerant Levels

The Problem

Refrigerant—sometimes called Freon or Puron depending on the system's age—is what actually moves heat out of your home. When levels drop, your AC blows warm air or runs endlessly without cooling. You might hear a hissing sound near the lines. Low refrigerant is almost never a matter of the chemical simply running out over time; it almost always means there's a leak somewhere in the system.

The Fix

This one is not a DIY job. Adding refrigerant without finding and sealing the leak is a short-term patch that drives up costs and harms the environment. A licensed technician will locate the leak, repair it, and recharge the system to the correct pressure. Older Milwaukee-area systems running R-22 (Freon) face an added wrinkle: that refrigerant has been phased out, so a leak may be the push you need to evaluate a full system replacement.

2. Dirty or Clogged Air Filters

The Problem

A clogged filter is the single most preventable AC problem. When airflow is restricted, the system works harder, cools less, and wears out faster. Homes with pets, older ductwork, or dusty basements—common in Milwaukee's brick two-flats and Cape Cods—tend to see filters clog quicker than the packaging suggests.

The Fix

Check your filter monthly. Replace it every one to three months, or more often if you have pets or allergy concerns. It's a two-minute task that protects a $5,000-plus system. The filter sits in your furnace or air handler; slide out the old one and slide in a new one with the airflow arrow pointing toward the blower.

3. Clogged Condensate Drain Line

The Problem

As your AC cools the air it also pulls moisture out of it. That condensate drains through a PVC line. In Milwaukee's humid summers, algae and mold build up in that line faster than in drier climates. A blocked drain causes the pan to overflow, trips a safety shutoff, and sometimes produces a musty smell before you ever notice the standing water.

The Fix

For minor clogs: turn off the system at the thermostat and breaker, then pour a cup of diluted white vinegar into the access port of the drain line. A wet/dry vac on the outdoor end of the line can pull the blockage out. If that doesn't clear it, or if you're seeing water damage near the air handler, call a technician. They have tools to flush the line completely without risking a secondary water problem.

4. Fan Motor Failure

The Problem

Your AC has two fans: the condenser fan in the outdoor unit and the blower inside. Both move heat and air in opposite directions, and both can fail. Grinding, squealing, or buzzing sounds from either unit are early warnings. A fan that spins intermittently or doesn't spin at all will leave the system overheating or circulating nothing at all.

The Fix

Check the outdoor unit for leaves, grass clippings, or debris jammed in the cage—power off first, always. Clear any obstruction and see if the fan spins freely. If the blades are bent or the motor hums but won't turn, the issue is internal. Fan motors and capacitors are not DIY territory; a technician can test the capacitor (a common culprit) and replace whichever component has failed.

5. Compressor Problems

The Problem

The compressor is the core of the outdoor unit. It pressurizes the refrigerant and keeps the entire cooling cycle moving. When it fails, the system doesn't cool at all. Compressors can fail from electrical issues, overheating, or low refrigerant causing slugging. This is one of the most expensive AC repairs—sometimes $1,200 or more just for the part.

The Fix

There's no homeowner fix for a failed compressor. A technician will diagnose whether the problem is the compressor itself, a failed capacitor, or an electrical fault feeding it. On older systems—ten-plus years is common for Milwaukee homes that bought systems in the early 2010s—a failed compressor often makes replacement more cost-effective than repair. Burkhardt's technicians will walk you through the numbers honestly before you commit to either path.

6. Frozen Evaporator Coil

The Problem

The evaporator coil sits inside your air handler and absorbs heat. When airflow is restricted—usually by a dirty filter or closed vents—moisture freezes on the coil. You'll notice reduced airflow, ice forming on the copper refrigerant lines, or water pooling near the unit as the ice melts. This is more common during Milwaukee's muggy late-summer stretches when the system runs hard and never gets a break.

The Fix

Turn the system off and switch the fan to "on" (not "auto") to let the coil thaw—this can take a few hours. Do not run the AC until it's fully thawed; running it frozen damages the compressor. Once thawed, replace the filter and reopen any closed vents. If it refreezes, the cause is likely low refrigerant, and you'll need a technician.

7. Electrical Control Failures

The Problem

Capacitors, contactors, and circuit boards are the electrical backbone of your AC. They wear out, particularly in systems that cycle on and off frequently—which happens a lot during Wisconsin's volatile spring weather when a 40-degree morning follows a 70-degree afternoon. A failed capacitor is one of the most common "AC won't start" calls in summer.

The Fix

Reset the circuit breaker once—if the system trips it again, stop. Repeated resets on a tripping breaker can damage the compressor. Capacitors look like metal cylinders inside the outdoor unit; a bulging or leaking capacitor is a clear sign of failure. Replacement is affordable (usually $100–$300 with labor) but needs a licensed technician to handle safely given the stored charge inside even a de-energized capacitor.

8. Thermostat Malfunctions

The Problem

The thermostat tells the system what to do and when. A failing thermostat—or one that's simply miscalibrated—results in the system running too long, short-cycling, or not turning on at all. Placement matters too: a thermostat on a south-facing wall in Bay View that gets afternoon sun will read warmer than the rest of the house and run the system unnecessarily.

The Fix

Check that the thermostat is set to "cool" and that the set temperature is below the current room temperature. Replace the batteries if it's battery-operated. If the display is blank or the system doesn't respond, the thermostat itself may need replacement. Upgrading to a programmable or smart thermostat is one of the better low-cost efficiency moves available to Milwaukee homeowners who aren't already using one.

Know When to Call for Help

Some AC problems are genuinely easy to fix yourself. Others—refrigerant leaks, compressor failures, electrical faults—need a licensed HVAC technician with the right tools and certifications. Attempting those on your own risks personal injury and can void the system warranty.

If your AC is struggling this summer anywhere in the Greater Milwaukee area—Brookfield, Brown Deer, Germantown, Waukesha, or anywhere in between—Burkhardt Heating, Cooling, Plumbing & Electric has been keeping local homes comfortable for decades. Call (414) 355-5520 to schedule a diagnostic.