ok i need suspension help

this is what happens , usually when the weather changes overnight it will lower itself (rear suspension air)also and this is the serious part...it will happen when i am driving at whatever speed , now i am aware that it will self adjust when i first start out driving , but after about 5 minutes the compressor i am sure is overworked due to constant adjusting , if i shut down motor and let it sit a while sometimes up to an hour it will readjust upon starting only to deflate again 5 minutes later , is there a sensor that is telling it to keep adjusting as everything else seems to be in working order .. when inflated i dont here any hiss , only when it chooses to deflate and only when running (in good weather) when not running it will stay inflated for days .....99 series ii discovery v8