So the '87-'91 trucks with factory A/C have a recirculation door in their HVAC system, it's there to cut off outside air and keep running only in-cab air through the blower. It's vacuum controlled, and only cuts outside air when you put the control lever to "off" or "max A/C". I found on FSB board that the problem with this is when you have -10 ambient temperature with some -20 windchill, heating up that air good could be a challenge for a truck with an aging heater core or tired blower fan.
Just to see how much of difference it actually makes I zip-tied my recirculation door closed, thus running inside air through the HVAC system all winter long - things got real warm real quick, noticeable improvement even when truck is stationary. For the warmer days tho I want the recirculation door open so I can get fresh air in the cab as I drive... So I devised and implemented a solution in my '90 truck - I zip tied the vacum pot closed which means I can get tons of heat in the winter even with some -20 degree temperature sand summer time i can snip it off!
the '92-'96 trucks utilize the same recirculation door setup as the '87-'91, so it should be possible to do this mod to one of these truck as well .
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____________________ 90 bronco ,351 auto 6"lift ,315/75/16 baja claws 9000lb tabor winch ,on board air
just an old truck .
If it aint broke ,fix it till it is
Allen
