355 HVAC Vent actuature/direction problems: Comments

I though I would post this because I have read several posts about problem the direction control of the HVAC vents. In some instances I have read that it just stopped working. In other cases that it constantly goes to the defroster and can't be changed by the console rotary switch when in manual mode. I just want to relate my experience with directional control. First, if it just stops working it's probably the vent actuator motor or a bad chip in the HVAC ECU under the hood. In my case I notice over a period of time, when I would stat the car the vent would go through some cycle and the stop at the desired position, or so I though. Since I have a spider, I seldom use the HVAC system. Over some period of time, I noticed that it was making noise when doing this and sometime last year of the year before it stopped altogether. I removed the actuator motor and found it basically inop. Fortunately I was able to obtain a new OEM unit. Form more recent posts I seem to have gotten the last one on the planet.

That was at least a year ago. I had never gotten around to installing it. While apart I just set the position for the center dash vent and left it that way until this week. So this week I installed the new actuator. When I was done I turned on the ignition to see if it work. The vent cycled from floor to defroster and stopped at defroster. I tried to change the position using the console rotary switch and nothing! I though, this sounds familiar.But not to panic. I disconnected the actuator and connected it directly to 12V and set the position to dash vents. The reconnected it to the ECU plug and turned on the ignition. Same behavior; cycled to floor, then to defrost where it stayed. At first I was thinking that maybe I burned of the chip in the ECU by reconnecting the old jammed actuator motor. But quickly ruled that out because, well, the vent moved through the cycle, so it was getting power from the ECU. Additionally, I was sure I read somewhere in the owner's or WSM that if the outside temperature or coolant temperature was below a certain level the HVAC ECU move the vent position to defrost to prevent cold air form being directed at the occupants if the controls were set to auto and it was cold out. And there it would remain until the coolant rose to a specific temperature. A quick search of the manual was to no avail. I couldn't find any comments verifying that function. But being confident that I had, and that is was somewhat cool the day I installed the new actuator motor, I dismissed it as normal. Today I took the car out for a drive. It was a beautiful day in New England and a sunny, clear warm 77 degrees. Since the battery had been disconnect while installing the new actuator motor and since my car is a 2.7 I had to let it idle for 10m minutes for the engine ECU to relearn. Once ready, I got in and turned on the blower which the controls were in manual mode. Surprise, surprise, the air blew from the center vent. A check with the rotary control and I could selected any of the vent positions. It was working perfectly. So I conclude that indeed, either the outside temperature or coolant temp must be above a specified level before the vent position rotary switch will control the vent position.

Thus, If you are having a problem with the vent position, first verify that the motor is good. This can be done by unplugging the actuator from the HVAC ECU and connecting 12V directly to the black and red wires at the plug. (You will first need to remove the center and right side vents, disconnect the battery and remove the passenger's air bag to gain access to the actuator motor and connector. *** IMPORTANT NOTE: DO NOT TRUN ON THE IGNITION WITH THE AIR BAG DISCONNECTED OR YOU MAY GET AN AIR BAG LIGHT THAT MAY REQUIRE AN SD2 TO RESET ***. You may have to try both polarities if the vent is at a max position, but it should move. If not, the actuator motor is bad or jammed (the internal gears break). If the motor functions correctly, then it would appear that, assuming you have checked the operation with the car up to temperature, there is most likely a problem with the ECU or temperature sensors. Again, this can be checked by setting the position to anything but defrost with a battery, and then reconnecting to the HVAC ECU, making sure the rotary switch is in any position but defrost, and with all controls in manual, turn on the ignition and see if the position returns to defrost. If it returns to defrost I believe you can conclude the ECU is ok and that the problem lies with one of the afore mentioned temperature sensors. If not it may be because the outside and coolant temperatures are above the required minimum. Thus, try to change the position using the rotary switch. If it remains in the center vent position regardless of the switch position, then it would appear that the ECU is not providing power to the actuator motor and most likely need a chip replace.

I can not guarantee that this diagnostic procedure will solved every problem but based on my experience I believe it should isolate some possibilities. Just be sure that you disconnect the battery before removing the air bag, and make sure the air bag is connect before turning on the ignition after reconnecting the battery.

 

Apologize for the misspelling in the tittle.

 

By the time I reread it I could not edit out the typos. It's a problem of fat finger, poor typing skills and dyslexia. From, form; sometimes I can't tell the difference.

I'm wondering if the cycling thing could have to do with the battery disconnect and the HVAC ECU needs to relearn. Starting with the vent set to dash the actuator cycled to floor, then reversed to defrost and stopped. It's expected to get cool tonight so maybe tomorrow morning I will check to see if the vent goes to defrost. But the cycling of the vent, even if it's battery disconnect related, shows that the ECU is functioning correctly. In any event, I think what I tried to convey should be helpful for those with the problem. Of course, if you have an SD1 or 2 you can just run a diagnostic on the HVAC system.

 

Just wanted to close the loop on this. The cycling of the event to flood then the defrost in manual mode and stopping in the defrost position seems to be associated with a battery dis/reconnect. Then, once the car is brought up to temperature the vent can be positioned where ever I choose and it will remain there on the next start up. However, upon start up, when in manual mode, the vent position can not be changed from the last position it was in until the car is up to temperature. Bottom line, in manual mode the vent position can only be selected when the car is at operating temperature.

 

Just to fix it.