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Rec door shut and concerned about Carbon Monoxide

I have a 1990 300ZX 2+2 that I bought new many many years ago. Although it is no longer my daily driver, I still enjoy the car. One issue that I’m concerned about is that the Rec door is stuck shut (recirculating inside cabin air only). I’ve confirmed this by looking behind the glove box to see the door is in the shut position.
To get at the servo motor would require removing part of the dash which I’m not interested in doing.
My question is…although the Rec door is closed on this 300ZX, is fresh air still being pumped into the cabin? I’m concerned that if no outside air is entering the cabin and I get an exhaust leak, that carbon monoxide could build up to dangerous levels.
Am I safe?

I am not interested in fixing it and most manuals out there are not for the 300ZX. Even if they were, I seriously doubt they would give me the answer to the question I posted above.

Yes. The vent system still allows some outside fresh air into the interior in the recirculation mode.As long as there are no exhaust leaks you have nothing to worry about. But if you want to be safe, you could always carry a canary in the vehicle. If the bird cacks, stop the vehicle and get out.


When I was growing up, my parents had cars that were only recirculating heaters. The heater was a box containing a small radiator and fan that hung down under the dashboard. The heaters that brought in fresh air from the outside were devised for the Nash motor company by an engineer named Nils Erik Wahlberg in the late 1930s. He had done extensive wind tunnel tests and found that the pressure was lower inside the car than outside the car when the car was in motion. He then reasoned that inducting fresh air into the car would pressurize the cabin and keep the outside air from infiltrating the passenger compartment.
It wasn’t too long after that that most cars heated fresh air brought in from the outside. However, Wahlberg was ahead of most of the other manufacturers. The other manufacturers brought in air through a duct down low in front of the grille where it was more apt to pick up fumes from other cars. In fact, there was a lawsuit involving Buick where a motorist was killed while sitting in his parked car with the heater on and there was a car in front of the Buick that was parked with the motor idling. Nash brought in the air on the cowl just below the windshield.
I don’t think you need to worry. In the 1940s, we even had recirculating Southwind gasoline heaters made by the Stewart Warner company that burned the fuel right in the car.

Light aircraft have the crappiest exhaust systems known to man…Therefore, carbon monoxide poisoning is a major concern among pilots of these aircraft… Therefore, pilot shops sell inexpensive CO detectors, the canary Tester referred to, to give them fair warning to DO SOMETHING…Check eBay…

Car makers, even in 1990, were smart enough to bring in enough outside air to maintain positive cabin pressure no matter where the heater controls were set… Another feature they provided, the door windows WILL roll down! Try it and see!

If you’re still concerned, you can get an inexpensive carbon monoxide detector at and hardware store.

“Car makers, even in 1990, were smart enough to bring in enough outside air to maintain positive cabin pressure …”

Apparently not all car makers…I called the local Nissan dealer and their service tech said that once the Rec door is closed NO outside air enters the car from the heater/AC box.