When I have my Max AC on and accelerate my vents switch to the defroster vents and when I let off or drive at constant speed it come out of front vents again. I am thinking vacuum leak but havent found one. Also my fans in any selection sounds like a moan and air flow restriction....

Any help guys....thanks in advance.

 

what do you drive?

sounds like vacuum reservoir. on the newer ones it's mounted in the drivers side fender. check for an unhooked line by the abs box.

older ones there is a black ball, it could be cracked(leaking) as well

 

If air flow goes to defrost on acceleration only when it's set to the MAX AC position, (all other modes are OK) the recirc actuator circuit has a vacuum leak. That is the only position that the recirc circuit has vacuum applied. If there was a vacuum leak anywhere else in the system, it would act up in other mode positions. The vacuum line from the mode switch to the recirc actuator is orange. The actuator is located in the dash just above the passengers feet.

 

Sorry it is a 97 Blazer. Mine has a ball on the hood. I will try and find a leak as well.

 

Same diagnosis holds true for 1997. Check for leaks in the orange line from the mode switch up to and including the recirculate actuator diaphragm.