For years whenever I use heat or AC, I get a headache in 10 min unless I crack a couple of windows. True in a late model Camry, Crosstour and older CRV. Appears I am sensitive, but looking for a new car. Is any car maker is known for being attentive to air pressure impact?
Car interiors can not be increased or decreased in air pressure. The interior air pressure will always equal ambient air pressure since the cabin is not air tight. Cars are not like airplanes with sealed pressurized cabins.
GM has had “flow through ventilation” for over 40 years now. I believe most, if not all, have this type of ventilation system these days.
Agree. There are two settings on the HVAC controls. One for recirculate and one for allowing fresh air to come in. Make sure you use the outside air setting at least.
I’m going to disagree a little with the above posters. I think that the HVAC system can and will raise pressure slightly. How do I check for a water leak into a car around a windshield or door weatherstrip? Put the fan on high with fresh air, close all the doors and windows, and spray around the glass and doors with soapy water. You’ll see bubbles around a leak. So there must be at least enough pressure to blow bubbles.
Now is this enough to cause a headache? I don’t know.
I don’t know if or how anyone can avoid a slight pressure differential in a car.
Well I guess that makes sense. Fan pushing air in and creating a positive pressure in the cabin, Maybe cut fan speed down. Again would be a good use for those old vent windows or even the floor vents.
It’s an odd problem and if any slight pressure differential in the cabin is causing this then maybe you need to see a doctor. What about a ride in an aircraft or rapid changes in altitude while driving? That should cause all kinds of havoc if pressure differences are the cause.
The thought of CO or possibly evaporator mold bleeding into the cabin came to mind but it’s hard to pin that down on 3 cars.
I have problems with pressure changes in a plane so I alway use “Earplanes”. They are ear plugs that allow gradual pressure changes to the ears. Just use them for take offs and landings but work great. I wonder if they would help if they would be legal. Yeah, otherwise there may be some sinus issues causing the issues with pressure that a doc should evaluate.
How did you determine the cause of your headaches is air pressure?
I mean, the simple act of driving a vehicle at highway speed will drop the cabin pressure. A car is kinda, sorta shaped like an airfoil–flat on bottom, arched on top–and motion causes low pressure, that would be partially mitigated by running the blower. And if OP is that sensitive to air pressure changes, climbing or descending a 200’ hill should mess him up totally.
I think (absent proof positive of a pressure-based etiology) that something like an annoying frequency produced by the blower motor is to blame.
Agree with @meanjoe75fan
I don’t think we talking about big amounts of pressure differences. The air pressures generated in a plane just mimick the atmospheric pressures we are all subjected to and is much more substantial then a car. Just driving over hilly terrain can do more to change pressures then what nomally occurs in a car at rest. Though The human body easily adapts to differnt atmospheric pressure ( look at what divers put themselves through) , the sudden changes I feel can be irritating to sensitive people and yes, tighter environments can be problematic. It should not be a factor when leaving vents open for most people.
I suspect it’s more likely that OP has some sort of issue where drying out the nasal passages even slightly causes a headache, and the moving air does that. I second the recommendation that OP mention this at the next doctor’s visit.
The pressure difference isn’t enough for me to notice, much less than I feel going up 9 floors in an elevator. I’d agree that maybe it could be a lack of fresh air.
I wouldn’t discount the possibility of an exhaust leak (manifold, flange, etc.), as others have said.
That can definitely find its way into the cabin and cause air leaks
I’ve driven vehicles with exhaust leaks, and it can actually make you lightheaded very quickly
An evap/smoke machine will very quickly find any exhaust leaks
I don’t think the typical automotive heater blower has the power or capacity to increase cabin pressure by a measurable amount…But I suppose with sensitive instruments, a slight change could be detected…This is done on purpose to keep any exhaust fumes out of the car…
Unless a blower is powerful enough to do this to an empty sealed plastic bottle, it comes nowhere close to the pressure difference experienced by driving from Taos NM to Austin TX. 
I think there may be a slight increase in pressure inside the cabin. Nils Erik Wahlberg, an engineer for the Nash automobile company discovered that when a car was in motion, the pressure inside the car was less than the pressure outside. Therefore, outside air would work its way in around the doors, windows, etc. At the time Wahlberg was doing his work in the late 1930s, car heaters were a box under the dash that contained a radiator and a fan and recirculated the air inside the car. Wahlberg then concluded that if he brought in air from the outside and heated it, the car was actually warmer as the pressure inside the car was greater than the pressure outside and thus blocked air infiltration. The Nash fresh air heating system was known as “Weather Eye”. I remember reading in an old Consumer Reports that comparing Weather Eye to the heaters used in other cars was like comparing a modern forced air furnace to a coal stove. By the late 1940s, other manufacturers went to fresh air heating systems.
A side note on Wahlberg-- he also developed the integrated heating and air conditioning system where all the components were in the dash or under the hood. Earlier systems had the evaporator and fans in the trunk and the cool air was ducted up to the passenger compartment. I think Nash brought out this integrated air conditioning and heating system in 1954.
" Earlier systems had the evaporator and fans in the trunk and the cool air was ducted up to the passenger compartment"
That is correct!
Whether we are talking about the first auto A/C (Packard, in the early '40s), or the optional A/C of Chrysler, Lincoln, & Cadillac in the early ‘50s, it was the norm for the evaporator & fan to be placed in the trunk, with the cold air ducted to the back of the heads of the rear seat passengers. This had the potential to make for an uncomfortably cold draft on the back of these folks’ necks.
Just as an aside, office buildings are designed with a slight positive pressure so that air does not infiltrate. Lab buildings are built with a slight negative pressure so that the nasty stuff in the lab is contained in the lab. So just sayn’ if you have pressure problems in a car, you’d likely have problems in office buildings too. I don’t know about driving from NM to Tx though-that’s weird.
The Goldberg Brothers - The Inventors of the Automobile Air Conditioner
Here’s a little fact for automotive buffs or just to dazzle your friends.
The four Goldberg brothers, Lowell, Norman, Hiram, and Max, invented and developed the first automobile air-conditioner. On July 17, 1946, the temperature in Detroit was 97 degrees.
The four brothers walked into old man Henry Ford’s office and sweet-talked his secretary into telling him that four gentlemen were there with the most exciting innovation in the auto industry since the electric starter.
Henry was curious and invited them into his office.
They refused and instead asked that he come out to the parking lot to their car.
They persuaded him to get into the car, which was about 130 degrees, turned on the air conditioner, and cooled the car off immediately.
The old man got very excited and invited them back to the office, where he offered them $3 million for the patent.
The brothers refused, saying they would settle for $2 million, but they wanted the recognition by having a label, ‘The Goldberg Air-Conditioner,’ on the dashboard of each car in which it was installed.
Now old man Ford was more than just a little anti-Semitic, and there was no way he was going to put the Goldberg’s name on two million Fords.
They haggled back and forth for about two hours and finally agreed on $4 million and that just their first names would be shown.
And so to this day, all Ford air conditioners show –
Lo, Norm, Hi, and Max – on the controls.
Just could not help posting this old joke