Why Is My AC Running But Not Cooling? Michigan HVAC Tech Explains
It's 85 degrees outside in Warren, and your air conditioner has been running all afternoon. You can hear the outdoor unit humming. You feel air coming from the vents. But your house is still 78 degrees and climbing.
This is one of the most common AC problems we diagnose at NEXT Heating & Cooling during Michigan summers — and it's frustrating because the system appears to be working. The fan is running. The thermostat is set correctly. But you're not getting cold air.
After 35 years of HVAC services in Metro Detroit, we've seen this scenario hundreds of times. Sometimes it's a simple fix you can handle yourself. Sometimes it requires a trained technician with refrigerant certification and diagnostic equipment. The key is knowing which is which.
In this article, I'll walk you through exactly why your AC might be running but not cooling, what you can check on your own, and when it's time to call a professional. I'll also give you realistic cost expectations for common repairs we see in Southeast Michigan homes.
How Your AC Actually Cools Your Home
Before we diagnose the problem, it helps to understand what your air conditioner is supposed to be doing. Unlike a furnace that creates heat by burning fuel, your AC doesn't "create" cold air. It removes heat from the air inside your home and moves it outside.
Here's the simplified version of the refrigeration cycle:
The compressor (located in your outdoor unit) pressurizes refrigerant gas, making it extremely hot. That hot refrigerant flows through the condenser coil (also outside), where a fan blows outdoor air across the coil to cool the refrigerant down. The refrigerant then passes through an expansion valve, which rapidly drops the pressure and temperature.
Now cold, the refrigerant flows into the evaporator coil (inside your home, usually in the furnace cabinet or air handler). Your blower fan pulls warm air from your house across this cold coil. The refrigerant absorbs the heat from that air, cooling it down before it's blown back through your ductwork and into your living spaces.
The now-warm refrigerant travels back outside to the compressor, and the cycle repeats.
When your AC is running but not cooling, something in this cycle is broken. Either the refrigerant isn't absorbing heat properly, the airflow is restricted, or a component has failed. Let's look at the most common culprits.
7 Common Reasons Your AC Runs But Doesn't Cool
1. Dirty or Clogged Air Filter
This is the most common cause we see — and the easiest to fix. Your air filter's job is to catch dust, pollen, and debris before it reaches the evaporator coil and blower motor. When the filter gets clogged, airflow across the evaporator coil drops dramatically.
Without enough airflow, the refrigerant in the coil gets too cold and the coil starts to freeze. Ice buildup blocks even more airflow, creating a vicious cycle. You'll feel weak airflow from your registers, and the air might not be as cold as it should be.
In Michigan homes, especially during high-pollen spring and summer months, we recommend checking your filter every 30-60 days. If you have pets, a dusty home, or run your system constantly, you might need to change it monthly.
The fix: Replace the filter with a new one of the same size. If the evaporator coil is already frozen, turn the system off and let it thaw completely (4-6 hours) before restarting. If it freezes again after a filter change, you have a deeper airflow or refrigerant issue.
2. Low Refrigerant (Leak in the System)
Your AC was charged with a specific amount of refrigerant at installation — typically R-410A in systems installed after 2010, or R-22 in older units. That refrigerant should never run out unless there's a leak.
When refrigerant levels drop, the system can't absorb enough heat from your indoor air. The compressor keeps running, the fan keeps blowing, but the air coming out of the vents is barely cool or just room temperature.
Common signs of low refrigerant include:
- Ice forming on the refrigerant lines or evaporator coil
- Hissing or bubbling sounds near the indoor or outdoor unit
- The outdoor unit runs constantly but the house stays warm
- Higher-than-normal electric bills (the system works harder to achieve less cooling)
Refrigerant leaks typically occur at brazed joints, valve connections, or in the evaporator coil itself (especially in units over 10 years old). In Southeast Michigan's freeze-thaw cycles, outdoor line set connections can develop small leaks over time.
The fix: This requires a licensed HVAC technician with EPA 608 certification. We'll use electronic leak detectors and pressure tests to find the leak, repair it, evacuate the system, and recharge it to the manufacturer's specifications. Simply adding refrigerant without fixing the leak is a temporary band-aid that wastes money and harms the environment.
If you have an older R-22 system with a major leak, replacement might be more cost-effective than repair — R-22 refrigerant has been phased out and is extremely expensive. We covered this in detail in our article on the R-410A refrigerant phase-out.
3. Frozen Evaporator Coil
We mentioned this briefly under dirty filters, but a frozen evaporator coil can also be caused by low refrigerant, a failed blower motor, closed supply registers, or ductwork problems.
When the evaporator coil freezes, it can't absorb heat from the air passing over it. You might notice ice on the refrigerant lines near your furnace, or water pooling around the indoor unit as the ice melts.
In Michigan basements where indoor units are often located, humidity can make ice buildup worse. We've seen coils completely encased in ice during humid July weeks when homeowners didn't realize their filter was clogged.
The fix: Turn the system off and let the coil thaw completely. Check and replace the air filter. If the problem returns, call a technician to check refrigerant levels, blower motor operation, and ductwork airflow.
4. Dirty Condenser Coil
Your outdoor condenser unit sits outside year-round, exposed to dirt, grass clippings, cottonwood seeds (a Michigan summer staple), leaves, and debris. Over time, the condenser coil fins get clogged, preventing airflow and reducing the system's ability to release heat.
When the condenser can't release heat efficiently, the refrigerant stays too warm. That warm refrigerant can't cool your indoor air effectively, even though the system is running.
We see this frequently in Sterling Heights and Troy homes with landscaping close to the outdoor unit, or in properties where lawn service crews blow grass clippings directly into the condenser.
The fix: Turn off power to the unit at the disconnect box. Gently spray the condenser coil with a garden hose from the inside out (not high pressure — you'll bend the fins). Clear debris from around the unit and maintain at least 2 feet of clearance. For heavily soiled coils, a professional cleaning with specialized coil cleaner is more effective.
This is part of what we check during our AC tune-up service in Warren and throughout Southeast Michigan.
5. Failed Compressor
The compressor is the heart of your AC system — a powerful pump that pressurizes refrigerant and keeps it circulating. When the compressor fails, refrigerant stops moving through the system. The outdoor fan might still run, and your indoor blower will still push air, but there's no cooling happening.
Compressor failure is often caused by:
- Electrical issues (capacitor failure, contactor problems, power surges)
- Refrigerant contamination or loss of lubricant
- Running the system with low refrigerant for extended periods
- Age and wear (compressors typically last 10-15 years)
You might hear clicking, humming, or grinding sounds from the outdoor unit, or the breaker might trip repeatedly.
The fix: Compressor replacement is expensive — often $1,500-$3,000 including labor and refrigerant. If your system is over 10 years old, replacement of the entire outdoor unit (or the whole system) is usually the smarter investment. Our NATE-certified technicians will give you an honest assessment of repair vs. replacement costs.
6. Thermostat Issues
Sometimes the problem isn't the AC at all — it's the thermostat. If your thermostat is set to FAN instead of AUTO, the blower will run constantly but the compressor won't turn on. You'll feel air movement but no cooling.
Other thermostat problems include:
- Dead batteries (for battery-powered models)
- Incorrect temperature setting or programming
- Thermostat located in a hot spot (near a window, in direct sunlight, above a heat source)
- Loose wiring or a failed thermostat
In older Michigan homes with mercury thermostats, we've seen units mounted slightly off-level, causing inaccurate temperature readings.
The fix: Check that the thermostat is set to COOL mode and the temperature is at least 3-5 degrees below the current room temperature. Replace batteries if applicable. If the thermostat is old or malfunctioning, upgrading to a programmable or smart thermostat can improve comfort and efficiency. We discussed this in our guide to smart thermostats vs. programmable thermostats for Michigan homes.
7. Undersized System or Ductwork Problems
If your AC has always struggled to cool your home — especially on the hottest days — the system might be undersized for your square footage, or your ductwork might be poorly designed or leaking.
In Southeast Michigan, we see this frequently in:
- Homes with additions that weren't accounted for in the original HVAC design
- 1960s-1970s ranches with undersized ductwork and minimal insulation
- Finished basements where supply runs were added without proper load calculations
- Homes where previous owners installed the cheapest, smallest unit to save money
Ductwork leaks in unconditioned spaces (attics, crawl spaces, unfinished basements) can waste 20-30% of your cooled air before it reaches your living spaces. We covered this extensively in our post on fixing hot and cold spots in your house.
The fix: A proper Manual J load calculation determines the right size AC for your home based on square footage, insulation, window area, orientation, and local climate. Ductwork should be sealed with mastic (not duct tape) and insulated where it runs through unconditioned spaces. This is a job for a reliable HVAC contractor in Metro Detroit who takes the time to do it right.
What You Can Check Before Calling a Technician
Before you schedule a service call, there are a few things you can check yourself. These simple diagnostics can sometimes solve the problem — or at least give the technician useful information when they arrive.
1. Check and replace the air filter. This is the first thing we check on every service call. Locate your filter (usually in the return air duct or furnace cabinet), and if it's dirty, replace it. Run the system for 30-60 minutes and see if cooling improves.
2. Verify thermostat settings. Make sure the thermostat is set to COOL mode (not FAN or OFF). Set the temperature at least 5 degrees below the current room temperature. Replace batteries if you have a battery-powered model.
3. Inspect the outdoor condenser unit. Go outside and look at your condenser. Is the fan spinning when the system is running? Is there debris blocking airflow? Clear away grass, leaves, and weeds within 2 feet of the unit. Gently spray the coil with a garden hose if it's visibly dirty.
4. Check airflow at registers. Walk through your home and hold your hand up to supply registers. Is the airflow strong? Is the air noticeably cool? Weak airflow suggests a filter, blower, or ductwork issue. Warm air suggests a refrigerant or compressor problem.
5. Look for ice on the indoor unit. If you have access to your evaporator coil or refrigerant lines near the furnace, check for frost or ice buildup. If you see ice, turn the system off and let it thaw completely before restarting. If it freezes again, you need professional service.
6. Listen for unusual sounds. Grinding, squealing, or clicking sounds from the outdoor unit can indicate a failing compressor or motor. Hissing or bubbling sounds suggest a refrigerant leak. These require immediate professional attention.
When to Call a Professional HVAC Technician
Some AC problems are DIY-friendly. Others require specialized tools, refrigerant certification, and years of diagnostic experience. Here's when you should call a professional:
Anytime refrigerant is involved. Federal law requires EPA 608 certification to handle refrigerant. If you suspect low refrigerant, a leak, or refrigerant contamination, you need a licensed technician. Attempting DIY refrigerant work is illegal, dangerous, and can destroy your compressor.
When electrical components are failing. Capacitors, contactors, and compressor windings carry high voltage. Misdiagnosis can lead to expensive component damage or personal injury. Our technicians carry multimeters, amp clamps, and manufacturer wiring diagrams to diagnose electrical issues safely.
If the problem persists after basic troubleshooting. If you've replaced the filter, checked the thermostat, and cleared the condenser but the system still won't cool, the problem is beyond homeowner-level diagnostics. Continuing to run a malfunctioning system can cause secondary damage (like a burned-out compressor from low refrigerant).
When you see ice, water leaks, or unusual sounds. These are symptoms of serious problems that will get worse if ignored. Ice indicates airflow restriction or refrigerant issues. Water leaks can damage ceilings, walls, and flooring. Grinding or clicking sounds mean a component is failing.
If your system is over 10 years old and repairs are frequent. At a certain point, repair costs outweigh the value of keeping an old system running. Modern AC units are significantly more efficient (14-20 SEER vs. 10 SEER for older units), and new refrigerants are more environmentally friendly. We'll help you understand when replacement makes more sense than repair.
Emergency AC service in Southeast Michigan: If your AC fails during a heat wave (90°F+ outdoor temperatures), especially if you have young children, elderly family members, or health conditions affected by heat, don't wait. NEXT Heating & Cooling offers 24/7 emergency service throughout Macomb, Oakland, and St. Clair counties. We prioritize cooling emergencies during extreme heat events.
What a Service Call Looks Like at NEXT Heating & Cooling
When you call us because your AC is running but not cooling, here's what happens:
We show up on time. Our technicians respect your schedule. We'll give you a 2-hour arrival window and call 30 minutes before we arrive. No waiting around all day wondering when the HVAC guy will show up.
We listen to your description of the problem. How long has this been happening? When did you first notice weak cooling? Have you heard any unusual sounds? This information guides our diagnostic process.
We perform a systematic diagnostic. We don't guess. We check airflow, measure temperature split (the difference between return air and supply air), test refrigerant pressures, inspect electrical components, and examine the condenser and evaporator coils. We use calibrated gauges and diagnostic tools — not hunches.
We explain what we find in plain English. No jargon. No scare tactics. We'll show you the problem (a frozen coil, a failed capacitor, low refrigerant pressure readings) and explain why it's causing your symptoms.
We give you options, not pressure. If your compressor has failed and your system is 14 years old, we'll give you the cost to replace the compressor and the cost to replace the entire system. We'll explain the pros and cons of each option. We don't work on commission, so we have no incentive to upsell you. Our job is to give you the information you need to make the right decision for your home and budget.
We fix it right the first time. Our trucks are stocked with common parts (capacitors, contactors, thermostats, filters). For refrigerant work, we follow manufacturer specifications exactly — proper evacuation, accurate charging, leak testing. We don't cut corners.
This approach is part of what we mean by "changing contractor culture." It's how we've operated for over 35 years, and it's why homeowners in Mount Clemens, Sterling Heights, and throughout Southeast Michigan trust us with their HVAC systems.
Cost Reality: AC Repairs in Southeast Michigan
Let's talk about what AC repairs actually cost in Metro Detroit. Prices vary based on the specific problem, the brand and age of your equipment, and parts availability, but here are realistic ranges based on our 2026 pricing:
Diagnostic/service call fee: $89-$150. This covers the technician's time to diagnose the problem. Many companies (including us) waive this fee if you proceed with the repair.
Air filter replacement: $20-$50 depending on filter type and size. High-efficiency filters (MERV 11-13) cost more but provide better air quality.
Capacitor replacement: $150-$300. Capacitors are one of the most common failures in Michigan's hot summers. They're relatively inexpensive parts, but require electrical knowledge to replace safely.
Contactor replacement: $150-$250. Similar to capacitors — common failure, straightforward repair.
Refrigerant leak repair and recharge: $400-$1,500+ depending on leak location and refrigerant type. Small leaks in accessible line set connections are cheaper to fix. Evaporator coil leaks are more expensive and might warrant coil replacement. R-22 refrigerant (for older systems) is significantly more expensive than R-410A.
Blower motor replacement: $450-$800. Blower motors fail due to age, bearing wear, or electrical issues.
Evaporator coil replacement: $1,000-$2,000. Coil replacement requires refrigerant recovery, brazing, evacuation, and recharging — it's labor-intensive.
Compressor replacement: $1,500-$3,500. At this price point, especially for systems over 10 years old, full system replacement is often the better value.
Full AC system replacement: $3,500-$8,000+ depending on size, efficiency rating (SEER), brand, and installation complexity. We covered this in detail in our ductless mini-split cost guide and our post on heat pump vs. furnace costs for Michigan homes.
The Next Care Plan saves money on repairs: For $5/month ($60/year), our Next Care Plan includes two annual tune-ups (spring AC check, fall furnace check), priority scheduling, no service call fees, and 10% off all repairs. If you need a capacitor replaced ($200 typical cost), you save $20 plus the $89 service call fee — that's $109 in savings on one repair, nearly double your annual plan cost.
More importantly, regular maintenance catches small problems before they become expensive failures. A dirty condenser coil caught during a spring tune-up costs $0 to clean (it's included in the visit). That same dirty coil left unchecked can cause compressor failure — a $2,500 repair.
AC Not Cooling? We'll Diagnose It Honestly.
NEXT Heating & Cooling has been keeping Michigan homes comfortable for over 35 years. Our NATE-certified technicians will diagnose your AC problem accurately, explain it clearly, and give you fair pricing without the upsell pressure. Serving Macomb, Oakland, and St. Clair counties.
Schedule Your Service CallFrequently Asked Questions
If your AC is blowing air but it's not cold, the most common causes are a dirty air filter restricting airflow, low refrigerant due to a leak, a frozen evaporator coil, or a failed compressor. Start by checking and replacing your air filter. If that doesn't solve it, you likely need a professional diagnostic to check refrigerant levels and component operation.
Give the system 30-60 minutes of run time after replacing a dirty filter. If the evaporator coil was frozen due to restricted airflow, you'll need to turn the system off and let it thaw completely (4-6 hours) before restarting. If the system still doesn't cool properly after a filter change and full thaw, the problem is likely refrigerant-related or a failed component.
No. Federal law requires EPA 608 certification to purchase, handle, and add refrigerant to HVAC systems. More importantly, simply adding refrigerant without finding and fixing the leak is wasteful and can damage your compressor. Professional refrigerant service includes leak detection, proper evacuation, accurate charging by weight (not pressure), and leak testing — all of which require specialized equipment and training.
This usually indicates an undersized system or a refrigerant issue. When outdoor temperatures are moderate (70s-low 80s), the system can keep up. When it's 90°F+ in the afternoon, the system is working at maximum capacity and any deficiency becomes obvious. Low refrigerant, a dirty condenser coil, or an AC that's too small for your home's cooling load will all show this pattern. A Manual J load calculation and system inspection can identify the root cause.
We recommend annual AC maintenance every spring before cooling season starts. A professional tune-up includes cleaning the condenser coil, checking refrigerant levels, testing electrical components, lubricating motors, inspecting ductwork connections, and verifying proper airflow. In Michigan's climate with humid summers and freeze-thaw cycles, annual maintenance catches small problems before they cause mid-summer breakdowns. Our Next Care Plan includes spring AC and fall furnace tune-ups for $5/month.
It depends on the repair cost and the system's overall condition. For minor repairs under $500 (capacitor, contactor, thermostat), repair usually makes sense. For major repairs over $1,500 (compressor, evaporator coil), replacement is often the better investment. Modern AC systems are significantly more efficient (16-20 SEER vs. 10-13 SEER for 12-year-old units), and new refrigerants are more environmentally friendly. We'll give you honest cost comparisons for both options so you can make an informed decision.
Your supply air (air coming out of the vents) should be 15-20°F cooler than your return air (air being pulled into the system). If your thermostat reads 75°F and your supply air is 55-60°F, the system is cooling properly. If the temperature difference is less than 15°F, you likely have low refrigerant, restricted airflow, or a failing compressor. We measure this "temperature split" on every diagnostic call to assess system performance.