Road dust coming into cab

[Rubble]

My 81 crew is getting a lot of dust coming into the cab on gravel roads.This thing has a/c but nothing works anymore,no compressor & some lines are disconnected.This is the first a/c equipped square I've had so not real familiar with the system.Any other of my squares:'86,'87,and 2 '80s non air don't have this problem.I can run down a gravel road with drivers window down and little or no dust,but not with this crew.The heater/ac control is in off position also.I've had squares for 30 years and this is the only one I have had that much dust come in,the others can even run with rear slider open too.TIA
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