AC running but blowing warm air? A St. Louis HVAC company explains the 6 most common causes, what you can check yourself, and when to call the pros.
Few things are more frustrating than an air conditioner that runs all day but blows warm air, especially in the middle of a St. Louis summer, when the heat index climbs past 100 and your house feels like it is losing the fight. The good news: warm air from your vents usually traces back to one of six causes, and a couple of them are things you can check yourself in the next five minutes.
Very prompt response and very professional and conscientious repair service. Nick did a great job and is a very nice guy.
I apparently have an intermittent problem that did not occur today. Your technician was excellent and system is now working, so I will call if issue recurs. You have terrific associatyes.
Response from the owner:Thank you, Rich! We're glad to hear you had a great experience with our repair service. Nick will be pleased to know his efforts made a positive impression. We appreciate your feedback!
I can’t say enough wonderful things about Thomas Hoffmann Air Conditioning and Heating! Nick came promptly, which was such a relief, and from the very beginning, he was personable, professional, and incredibly honest.
After dealing with other companies, Nick’s honesty really stood out. He took the time to explain everything clearly, answer my questions, and make sure I understood what was going on—without any pressure or unnecessary recommendations. It was refreshing to feel like I was dealing with someone who genuinely cared about doing the right thing for the customer.
Nick’s professionalism, knowledge, and customer service were truly top-notch. I wouldn’t hesitate to recommend Thomas Hoffmann Air Conditioning and Heating to anyone looking for a heating and cooling company you can actually trust!
Response from the owner:Thank you for the 5-star rating, Lori!
Response from the owner:Thank you, Margaret! We appreciate your kind words and will make sure to pass along your praise to Nick for his excellent service.
Thomas Hoffman HVAC provides excellent service. The staff members are very nice, respectful and knowledgeable. I always feel comfortable with the advice I have been and the fees for repairs. Whether we see one of the companies employees or Thomas himself we have always had a good experience and highly recommend them. I am thankful to have found a trustworthy company to count on for my future needs.
Response from the owner:Thank you for the 5-star review, Lisa. We appreciate the support!
Nick did an outstanding job on checking the attic and replacing damaged insulation. He showed me where the leak was coming in from the roof. Excellent overall job
Response from the owner:Thank you, Jane! We're glad to hear that Nick provided exceptional service by checking the attic and addressing the insulation issue. Your satisfaction is important to us!
Response from the owner:Thank you, Hank, for your wonderful feedback; we're glad you enjoyed the fast, friendly, and professional service, and we'll be sure to keep up the great work!
I was distraught to find out our 20 year old HVAC needed to be replaced. Hoffman was beyond empathetic and took care of me within 24 hours during the heat wave. They were on time and very efficient. I have to have trust worthy people work on our house and be in our cocoon, therefore Hoffman has always been our contractor and always will be! They have become family;) I refer all of my clients to them!!!
Response from the owner:Thank you, Katie! We're so glad to hear that you felt supported during a tough time. Your trust means the world to us, and it's wonderful to know that we’ve become part of your family. We appreciate your referrals and look forward to continuing to serve you and your clients!
I called on a Monday morning as air conditioning was blowing warm air. They were able to come to my house very early afternoon and fixed the problem. Would highly recommend and will use them again.
Response from the owner:Becky thank you so much for your great review. We appreciate your business and your kind words.
Thomas Hoffmann provided outstanding service from start to finish. The technician was professional, knowledgeable, and took the time to explain everything clearly. They arrived on time(early), diagnosed the issue quickly, and had my AC running perfectly in no time. I really appreciated their honest recommendations and fair pricing—no pressure or unnecessary upselling. It's refreshing to work with a company that truly values customer service. I highly recommend Thomas Hoffmann to anyone looking for reliable, high-quality HVAC service.
Response from the owner:Spencer, thank you so much for the 5-star review. We really appreciate your kind words, & your business.
Outstanding...Giovani was superb..need him as a regular for our regular maintenance!
Response from the owner:Thank you, Brad! We're glad to hear you had a great experience with Giovani. We appreciate your feedback and will certainly keep your request in mind for your regular maintenance.
The repairman arrived at around 8:30 AM and spent about three hours working on the unit, which I purchased from them less than a year ago. At the end of three hours, he informed me that my unit was not working because I had the wrong filter in it. I raised a question about why it took three hours to replace the filter. I can't really explain his response because it was in technical jargon that I did not understand well enough to know what other questions to ask. The unit has a two year parts and labor warranty and a 10 year manufacturer parts warranty. unfortunately, I did not get the benefits of those warranties because, as the technician put it, the onus for using a less effective filter, rests with the customers. Then, he went on to describe to me the best filter choice, something the average customer would not automatically know. My greatest disappointment was being denied the benefits of my warranties.
On the plus side, once management became aware of my dissatisfaction, they reached out to me with an apology for any role they played in my dissatisfaction and, as a show of their good intentions, they shredded my check, subsequently, not charging me for their service. This response showed a genuine commitment to quality and efficient service, as well as a commitment to customer satisfaction. Consequently, I highly recommend Hoffmann Air Conditioning services.
Response from the owner:Thank you, James, for your 5-star rating; we truly appreciate your support!
My experience was very pleasant. Nick was great got my problem taken care of. He explained how to use my new equipment . Thank you for a true 24 hr service.
Response from the owner:Tiffany, thank you for the 5-star review. We appreciate you and your business!
Very prompt, conscientious and personable. Work well done.
Response from the owner:Thank you, Kathleen! We appreciate your kind words about our team's promptness and attention to detail. Your feedback means a lot to us!
The tech was great. He showed up on time, was very polite, answered all my questions and got the job done. The service was also very reasonably priced.
Response from the owner:Thank you, Lisa! We're glad to hear you had a great experience with our technician. Your feedback about punctuality, politeness, and value is much appreciated!
Technician, Giovanni Leone, did such a great job in fixing our AC on a Saturday morning when the Temp is supposed to get up to 100 degrees, later today! I felt like we were in excellent hands and he explained everything he was going to do and then explained in even greater detail once everything was done! I told him if he ever wants to go into sales, he should! He has great personable skills! We have used Thomas Hoffmann before for our heating and cooling needs and they are always professional and trustworthy! My only mistake was not having them to come out to check our AC in the past 3 years!
Response from the owner:Thank you, Bill! We're so glad to hear about your positive experience with Giovanni. It's great to know that you felt well taken care of and appreciated his thorough explanations. We truly value your trust in us for your heating and cooling needs, and we look forward to serving you again in the future!
He came early and identified the problem ordered the part and put it in. He was professional, neat in appearance. I would say an asset to your company.
Response from the owner:Thank you, Robinette! We appreciate your kind words about the professionalism and neatness you experienced. It's great to hear that our team member made a positive impact. Your feedback means a lot to us!
Nick came by, identified the problem quickly and had it fixed. Great service!
Response from the owner:Thank you, Ted! We're glad to hear that Nick provided you with quick and effective service. Your feedback is greatly appreciated!
1. Your Thermostat Is Set to “Fan On”
Start with the simplest culprit. When the fan is set to ON rather than AUTO, the blower runs continuously, even between cooling cycles, pushing room-temperature air through your vents. It feels warm, but nothing is broken. Switch the fan to AUTO, confirm the mode is set to COOL, and make sure the target temperature is below the current room temperature. A surprising number of “broken AC” calls end right here.
2. A Clogged Air Filter
A filter choked with dust and pet hair strangles airflow across the indoor coil. The system keeps running, but not enough cool air reaches your rooms, and in severe cases the coil ices over and the AC blows warm air until it thaws. St. Louis homes tend to clog filters faster than average thanks to long cooling seasons and high pollen counts. Check the filter and replace it if you cannot see light through it. This is also the single best habit for extending your system’s life between tune-ups.
3. A Tripped Breaker at the Outdoor Unit
Your AC is really two machines: the indoor blower and the outdoor condenser. If the outdoor unit loses power, the indoor fan keeps circulating air that never gets cooled. Check your electrical panel for a tripped breaker labeled AC or condenser. Reset it once. If it trips again, stop there and call us; a breaker that keeps tripping is protecting you from an electrical fault that needs a professional.
4. Low Refrigerant From a Leak
Refrigerant is what actually removes heat from your home, and the system does not “use it up.” If levels are low, you have a leak. Warning signs include warm air, ice on the refrigerant lines, hissing sounds, and cooling that fades over days or weeks. Refrigerant handling is regulated and requires certification, so this one is never a DIY fix. A technician can locate the leak, repair it, and properly recharge the system.
5. Dirty or Blocked Condenser Coils
The outdoor unit’s job is to dump heat from your house into the outside air. When its coils are coated in dirt, grass clippings, and cottonwood fluff (a St. Louis June classic), it cannot release that heat, and cooling performance drops fast. Gently clear leaves and debris around the unit, and keep a 2-foot clearance on all sides. Deep coil cleaning is part of a professional tune-up and often restores noticeable cooling power.
6. A Failing Compressor
The compressor is the heart of the system, and when it wears out, warm air is often the first symptom, sometimes with humming, clicking, or hard starts. Compressors tend to fail on older units, raising the repair-or-replace question that deserves an honest, written answer, not a sales pitch.
When to Call The Professionals
Check the thermostat, filter, breaker, and outdoor unit yourself. If the air is still warm after that, the cause is refrigerant, electrical, or mechanical, and running the system in that state can turn a repair into a replacement.
Warm air and no answers? Call Thomas Hoffmann Air Conditioning & Heating at (314) 471-7625, any hour, any day. A real St. Louis dispatcher picks up, and our AC repair team can often get to you the same day.
