Low flow at high throttle

[C420sailor]

Pimps,

Got the new fan blower motor and resistor in and the airflow is fantastic. Now I’d like to fix a problem I’ve had for a long time, but hasn’t bothered me until lately (doing a little light towing).

At mid-throttle and above, HVAC (manual controls) cuts airflow out the vents. Not sure if it’s being redirected out the defroster or just blocked all together. No change in fan RPM. Once I come off the pedal a bit, it flows again. I seem to remember @donalds talking about a vacuum line or reservoir leak that could cause this.

It didn’t bother me much before, but with the trailer I need more throttle for a given speed, and anything over 50-55mph on even flat road kills the air flow. Not fun.

Point me in the right direction?

 

[donalds]

Pimps,

Got the new fan blower motor and resistor in and the airflow is fantastic. Now I’d like to fix a problem I’ve had for a long time, but hasn’t bothered me until lately (doing a little light towing).

At mid-throttle and above, HVAC (manual controls) cuts airflow out the vents. Not sure if it’s being redirected out the defroster or just blocked all together. No change in fan RPM. Once I come off the pedal a bit, it flows again. I seem to remember @donalds talking about a vacuum line or reservoir leak that could cause this.

It didn’t bother me much before, but with the trailer I need more throttle for a given speed, and anything over 50-55mph on even flat road kills the air flow. Not fun.

Point me in the right direction?

Your are losing vacuum
It happens on a hill or under load
The vac ball can only hold if you have no leaks and the one way valve in it is working
I added a one way valve to the vac line and have no leaks
Still does it under load and or up a hill

If everything is in order in theory the system should work flawless
But in the real world the system acts like ours imo

 

[C420sailor]

Thanks, makes sense. Where is the ball located?

 

[donalds]

Under the air box in the inner fender liner
Follow the vac lines
They snap easy you may even find a broken one