Final answer:
The ride height control valve provides more air to air springs when the truck has a heavier load to maintain a constant ride height. A heavily loaded trailer bounces slowly because the load compresses the springs, leading to stiffer and slower suspension movements.
Step-by-step explanation:
The ride height control valve will supply more air to the air springs when more load is applied to the truck. The purpose of the ride height control valve is to maintain a constant ride height, so when additional weight is added, the valve adds air to the springs to compensate and keep the vehicle level.
Regarding the observed trailer behavior, if a trailer is bouncing up and down slowly, it is more likely that the trailer is heavily loaded. A heavily loaded trailer will have less suspension travel due to the load compressing the springs, causing slower bounces as the springs are stiffer. Conversely, an empty trailer would have a lighter load, allowing the suspension to move more freely and causing quicker, potentially more erratic bounces.