the only way to get "cool" outside air into the car is through the vent in the passenger side kick panel. it's basically a plenum with a flapper, actuated by a vacuum diaphragm, that seals against the cowl right behind the blower motor.
the valve/flap defaults to the closed, or "recirculate" position, with no vacuum applied. with vacuum applied the flapper closes against the cabin and allows for outside air to be drawn from the cowl, then blown through the evap box and into the cabin through the vents.
if the whole system is working properly and you have the control unit set to A/C and the temp lever to full cold, that will be the only way you get get "cool" outside air to blow from the vents. if that diaphragm is ruptured, otherwise inoperative, you'll essentially be running recirculated air all the time.
if the ambient air temps are say 80*, the air blowing through the vents will be at least that, so keep that in mind. also keep in mind the blower/heater core box isnt the highest tech when it comes to sealing, so depending on the condition of the internal seals and rubber flaps, you're always going to get some cross over heat coming through, it'll just depend on how much.
check to make sure that passenger side diaphragm is A - getting a vacuum signal when it's supposed to and, B - is actually working properly, closing up against the cabin.
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costs too much
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