Your dining room thermostat reads 72 degrees. Your customers are still complaining it feels hot. Kitchen staff are miserable by the lunch rush. Doors are hard to open, or they slam shut on their own. The AC is running constantly but can’t seem to keep up, and your energy bill keeps climbing with no obvious explanation.
Most restaurant owners in this situation call for an AC repair. Often, the AC isn’t the problem at all.
What Make-Up Air Is and Why It Controls Everything Else
Every time your kitchen exhaust hood runs, it pulls a significant volume of air out of your building. That air has to be replaced. The system responsible for replacing it is called make-up air, and in most commercial kitchens it’s either undersized, poorly balanced, or not functioning the way it was designed to.
The physics are straightforward. Air exhausted out of the building has to be matched by air coming in. When it isn’t, the building develops negative air pressure. That negative pressure is what makes your front door feel like it’s fighting you every time a customer tries to enter. It’s what causes back-drafts around your cooking equipment. And it’s what forces unconditioned outdoor air to infiltrate through every gap and crack in the building envelope rather than coming in through a controlled, conditioned supply.
In South Texas, that infiltrating air isn’t just warm. It’s humid. When a restaurant in the San Antonio area is operating under negative pressure during a July lunch service, it’s essentially pulling 95-degree, 70% humidity air through every unsealed gap in the building. Your AC system then has to condition all of that infiltration on top of everything else it’s already managing. No system is sized for that load, which is why the thermostat reads one number and the room feels like another.
How South Texas Makes This Worse Than Most Places
Make-up air problems exist in restaurants everywhere. In South Texas, the consequences are significantly more severe for two reasons. The outdoor air is hotter and more humid than almost anywhere else in the country for more months of the year, and the temperature differential between outside and inside is extreme for a longer operating season.
When a make-up air unit brings in unconditioned outdoor air at 98 degrees and dumps it into a kitchen that’s trying to stay at 75, the HVAC system absorbs that entire thermal load in addition to the heat coming off the cooking equipment. The International Mechanical Code requires that the temperature differential between make-up air and the conditioned space not exceed 10 degrees. In a South Texas summer, untempered make-up air can come in 25 degrees above that threshold. The system can’t compensate, and the kitchen stays hot no matter how hard the AC runs.
Humidity compounds the problem further. Restaurants already generate significant moisture from cooking, dishwashers, and occupancy. Add humid outdoor air infiltrating through a pressure-imbalanced building and you get condensation on surfaces, persistent clamminess in the dining room, accelerated mold risk in drain pans and ductwork, and a general sense that the building never quite feels right even when the temperature is technically correct.
The Signs Your Make-Up Air System Is the Problem
Most of these symptoms get misdiagnosed as AC problems, which is why restaurants end up paying for repairs that don’t fix anything.
- Doors that are difficult to open or slam shut on their own are a direct indicator of negative building pressure. The exhaust system is pulling more air out than the make-up air system is replacing.
- Kitchen odors migrating into the dining room consistently point to airflow imbalance. A properly pressurized restaurant keeps kitchen air moving toward the exhaust hood and away from the dining space. When that balance breaks down, cooking smells travel the wrong direction.
- An AC system that runs constantly without hitting setpoint in the dining room, especially during peak service, often means the unit is fighting infiltration load it was never designed to handle rather than a failing compressor or low refrigerant.
- Unusually high humidity in the dining room during service, where the space feels sticky or clammy despite the AC running, suggests the system is losing the battle against moisture-laden infiltration air.
- Grease building up in unexpected places, on walls away from the cooking line, on surfaces near doors and windows, indicates that exhaust airflow is not being captured and directed the way it should be.
What a Proper Diagnosis Actually Looks Like
Fixing a make-up air problem is not the same as servicing an AC unit. It requires someone who understands how the kitchen exhaust system, the make-up air unit, and the building HVAC interact as a system rather than as separate pieces of equipment.
A proper assessment measures building pressure to confirm whether negative pressure exists and how severe it is. It evaluates whether the make-up air unit is sized correctly for the exhaust volume the hood system is moving. It checks whether the make-up air is being tempered before it enters the building, which in South Texas is not optional during summer. And it looks at how the dining room HVAC is interacting with kitchen ventilation to identify where the imbalance is coming from.
Many South Texas restaurants are running systems that were installed or last serviced before the refrigerant transition, before current energy costs, and sometimes before the restaurant’s menu or equipment lineup changed. A kitchen that added a fryer or a second commercial range since the original HVAC design was done is almost certainly running on an exhaust and make-up air system that was never sized for its current load.
Murray Air Conditioning Has Served South Texas Restaurants Since 1995
Murray Air Conditioning has been working with commercial clients across La Vernia, San Antonio, Floresville, New Braunfels, and the surrounding area for 30 years. Their licensed technicians understand the specific demands that South Texas heat and humidity place on restaurant ventilation systems, and they work across the full scope of commercial HVAC including make-up air assessment, system balancing, and kitchen exhaust integration.
If your restaurant is experiencing any of the symptoms above and your current service calls haven’t resolved them, the issue may not be the AC unit. Contact us today to schedule a commercial assessment and find out what’s actually driving the problem.
