A/C Vents not functioning correctly

[AWhite91]

Sometimes when I start my truck with the A/C on Max Cool and the fan set to max, it blows very weak like the fan speed is on low. It takes turning the main control knob to Off then back to Max Cool for it to blow like it should. Any ideas as to what may be causing this?

[STurbo90]

the hvac is actuated by vacumn and may be weak when first started.

[AWhite91]

Sorry, I forgot to add this. Sometimes it doesn't blow as it should until after turning the switch on and off as I said before, regardless of how long the truck has been running. I just started it a few minutes ago and it worked as it is supposed to (only took a few seconds to build vacuum).