2001 olds silhouette - no airflow at defrost vent when in defrost
Blower works on all speeds and in all settings. airflow at panel and floor is ok. air temp is ok. cabin filters are clean. when in defrost mode - blower runs on all speeds but there is no air discharged at defrost vent. Any suggestions appreciated. Thanks.
Re: 2001 olds silhouette - no airflow at defrost vent...
On cars anywere from about 92 or so and up, they do not use linkage anymore to move the the flaps that direct the air above or below the dash. Now they all run by electrical servos. What that means is that when you turn the nob, your not actually moving a metal bar to move the system. Your telling a sensor to move the flaps into the position you desire. There could be a few problems here. It could be the electical motor it self, or could be, what Im assuming, a rotory nob, which is actually called a retrostat, is not hitting the proper connections due to wear, or even dust. This may be a problem you want to put up with, becouse to diagnose the problem its self will not be cheap. If the nob is the problem, you have to replace the whole unit its self. Depending, it should run around for your vehical $200 or so. I hope this helps. John...
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Air Flow Control
Air flow control is accomplished in the following manner:
Primary control is through the function selector knob , mounted on the heater function selector switch, which is part of the heater control .
The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
The heater function selector switch combines a vacuum selector valve with an internal electrical switch.
The vacuum selector valve directs source vacuum to various vacuum control motors (18A318) . Refer to the System Airflow Schematic and Vacuum Control Charts.
An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch (18578) .
The position of the function selector knob determines the manner in which the system will operate.
Each position of the function selector knob is detented for positive engagement.
You probably have a vacuum leak , Pull heater control panel an check for vacuum . A broke vacuum hose or The vacuum selector valve is bad ! Or check for a vacuum hose in the engine compartment being off somewhere !
i'd think that the vent adjuster knob/slider is not working correctly strip out the heater panel around the control knobs and check the vent direction is working properly either stiff operation so a little wd40 on the cable would probably do the trick or some thing causing the vent itself to not move
The blower motor is either bad, or if you hear it blowing in the front but nothing comes out of the vents, then it's a vacuum motor problem. The flaps aren't angled right to allow air to come out of the vents (either for a/c, heat, or defrost).