air compresser ?

hi i have a renault midliner s160 turbo 1995 10 ton whilst driving it i came to a gradual stop but found the brake pedal go hard luckily there was no vehicles ahead off me so coated it into a laybay got towed back on a straight bar wot would have caused this there was no ovious signs off broken pipes or any think leaking etc the recovery guy said the compresser outlet was weak ? could this cause the problem no warning lights come up on the dash now its not building any air wot so ever the air brakes are locked on thus unable to drive or move the truck any tips possible causes etc common known faults any help advice much helpful thanks .