355 HVAC Selector Switch Not Working--Please help!!!

My A/C always blows a little out the defrost vents. I still get a lot through the regular vents too but if I leave it on high sometimes I get some condenstation on the windshield from the cold air blowing on it.

I'm going to try pulling the timing actuator to inspect it this week. Maybe a little WD-40 will help.

Has anyone else had this problem?

 

resurrection.....I'm having this issue where air always blows out of the defrost vents.....along with where the air should be coming out. My fresh air divert flap is also broken/currently removed. Would the absence of the fresh air diverter flap cause this or is it something else.

 

The diverted flap if it is open would make your a/c inefficient but has nothing to do with the air coming out only the defroster. I had same problem. You need new chips in the hvac ecu. I just had mine changed and now works great. Pro Audio Florida did my Ecu. Cost around $200.

 

thanks Bob !
My air comes out of all the different vents as it's supposed to.

The issue is that air comes out of the Defrost vents at all times regardless of what other vents have been selected and are pumping out air.
This is different than your situation where air only comes out of the Defrost vents.

correct ?

 

Yes. Maybe one of the "flaps" that blocks air from going to the defroster is broken.

 

Would anyone have a photo of the rotating cylinder? I'm wondering how the air is diverted to various vents. Do the vanes have seals on them which leak? It's hard to tell from online photos:



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Doesn't look easy to disassembly.

 

It's easy to disassemble. Just a few screws and it pulls apart. I will try to remember to take pictures tomorrow. I have an extra that is apart.

 

Can anything be done in-situ, Bob? Is it a dash out job?

 

The cylinder is just a cylinder with a slot through it. It does have a sponge rubber lining, probably for noise suppression, but no real seals. Where air goes is simply a matter of to the position of rotation: floor, dash, windshield, or multiple vents. The unsealed gap is pretty small, but there would be some leakage. However, the air will predominantly follow the path or least resistance, thus if a single direction is selected then there should be little flow to the others. Excessive, constant flow to the defroster vents would most likely indicate a failed or stuck actuator motor, or a problem with the HVAC ECU.

I have read or heard that there is also the possibility that if the outside air temp sensor fails the unit defaults to defroster. However, I have not been able to verify that.

I can't see the need to disassemble. You need to remove the center and right vents from the dash and remove the air bag to get at the actuator motor. Once the actuator motor is removed the cylinder rotates freely. So easy to check if it's binding on something.

 

Sound plausible. The sensor element has a negative temperature coefficient. An open circuit may be seen as a really low outside air temperature. I assume it will only do this in auto (distribution) mode.

Bob was talking earlier about broken flaps (vanes?). I was thinking perhaps you'd need to visually inspect the vanes if this was the case.

 

My ecu chips failed so I only got air out of the defroster vent which is the default. I did not get any air out is other vents as the original poster does. I could move the switch to other positions and still nothing out of other vents, I checked my outside sensor and it was ok. The divertor motor can be unmounted and the harness connected and see if motor turns and stays in different positions when switch turned. If it moves but then turns back to the defrost position, it is the chips. Motor can be checked with 12 volt source to see if it moves at all. If not, bad motor. You can also check the drum by removing the motor, but a screw driver in the drum slot and rotate it with the a/c on and fan on high and see if you can move to other positions and see if air comes out of diffent vents without coming out of defrost vent. To check the outside temp sensor is a pain because it is in outside mirror and door panels need to be removed, mirror taken apart and harness fished through door panel. Avoid if possible.

 

Couldn't you have more easily checked the sensor resistance at the door connector or ECU?

I can't see how the system would get a proper reading of outside air temperature by having a sensor stuck out in the airstream. Wouldn't the temperature vary with speed (wind chill). The occupant being sheltered inside the car wouldn't be subjected to that same cooling air. I guess ram air heating would be insignificant at most car speeds.

 

I thought wind chill was just pertaining to skin.

 

Possibly. I did think about that, but then confused the issue in my mind by thinking about radiators being cooled by airflow. I guess, however, in the case of radiators and humans, you have a hot fluid (coolant/blood) that can never be cooled below the temperature of the air.

Many aircraft have temperature sensors which are mounted on the nose and can be heated by radiant heat from the sun when sitting on the ground, giving a false reading. To get a proper reading of air temperature, ambient air is drawn into the sensor by a venturi generated by compressed air. I guess in the case of the mirror-mounted sensor (which also gets radiant heat from the sun) the airflow will actually give a more accurate reading?